Patent Publication Number: US-2023165133-A1

Title: Organometallic compound and organic light-emitting device including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority to Korean Patent Application No. 10-2021-0164867, filed on Nov. 25, 2021, in the Korean Intellectual Property Office, and all the benefits accruing therefrom under 35 U.S.C. § 119, the entire content of which is incorporated by reference herein. 
     BACKGROUND 
     1. Field 
     One or more embodiments relate to an organometallic compound and an organic light-emitting device including the same. 
     2. Description of the Related Art 
     Organic light-emitting devices (OLEDs) are self-emissive devices, which have improved characteristics in terms of viewing angles, response time, brightness, driving voltage, and response speed. OLEDs may also produce full-color images. 
     For example, an organic light-emitting device includes an anode, a cathode, and an organic layer located between the anode and the cathode, wherein the organic layer includes an emission layer. A hole transport region may be located between the anode and the emission layer, and an electron transport region may be located between the emission layer and the cathode. Holes provided from the anode may move toward the emission layer through the hole transport region, and electrons provided from the cathode may move toward the emission layer through the electron transport region. The holes and the electrons recombine in the emission layer to produce excitons. These excitons transition from an excited state to a ground state, thereby generating light. 
     SUMMARY 
     One or more embodiments include an organometallic compound and an organic light-emitting device using the same. 
     Additional aspects will be set forth in part in the detailed description which follows and, in part, will be apparent from the detailed description, or may be learned by practice of the presented exemplary embodiments herein. 
     According to an aspect, provided is an organometallic compound represented by Formula 1: 
       M 1 (L 11 ) n11 (L 12 ) n12    Formula 1
 
     wherein, in Formula 1, 
     M 1  is a first-row transition metal of the Periodic Table of Elements, a second-row transition metal of the Periodic Table of Elements, or a third-row transition metal of the Periodic Table of Elements, 
     L 11  is a ligand represented by Formula 1-1, 
     L 12  is a monodentate ligand or a bidentate ligand, 
     n11 is 1, 
     n12 is 0, 1, or 2, 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 1-1, 
     * 1  to * 4  each indicates a binding site to M 1 , 
     ring A 20 , ring A 30 , and ring A 40  are each independently a C 5 -C 30  carbocyclic group or a C 1 -C 30  heterocyclic group, 
     T 1  is a single bond, *—N(R 1 )—*′, *—B(R 1 )—*′, *—P(R 1 )—*′, *—C(R 1 )(R 2 )—*′, *—Si(R 1 )(R 2 )—*′, *—Ge(R 1 )(R 2 )—*′, *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O) 2 —*′, *—C(R 1 )═C(R 2 )—*′, *—C(═S)—*′, or *—C≡C—*′, 
     T 2  is a single bond, *—N(R 3 )—*′, *—B(R 3 )—*′, *—P(R 3 )—*′, *—C(R 3 )(R 4 )—*′, *—Si(R 3 )(R 4 )—*′, *—Ge(R 3 )(R 4 )—*′, *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O) 2 —*′, *—C(R 3 )═C(R 4 )—*′, *—C(═S)—*′, or *—CEC—*′, 
     X 11  is C(R 11 ) or N, X 12  is C(R 12 ) or N, X 13  is C(R 13 ) or N, and X 14  is C(R 14 ) or N, 
     X 20  is C or N, X 21  is C or N, and X 22  is C or N, 
     X 30  is C or N, X 31  is C or N, and X 32  is C or N, 
     X 40  is C or N, and X 41  is C or N, and 
     Ar 1  is a group represented by Formula 2, 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 2, 
     E 1  is a C 1 -C 60  alkyl group substituted with deuterium, or a substituted or unsubstituted C 1 -C 60  aryl group, 
     E 2  to E 5  are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, —SF 5 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 1 -C 60  alkylthio group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 7 -C 60  alkyl aryl group, a substituted or unsubstituted C 7 -C 60  aryl alkyl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted C 2 -C 60  heteroaryl alkyl group, a substituted or unsubstituted C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —N(Q 1 )(Q 2 ), —Si(Q 3 )(Q 4 )(Q 5 ), —B(Q 6 )(Q 7 ), —P(Q 8 )(Q 9 ), or —P(═O)(Q 8 )(Q 9 ), at least one of E 2  to E 5  is not hydrogen, with the proviso that when E 1  is a C 1 -C 60  alkyl group substituted with deuterium and E 5  is a C 1 -C 60  alkyl group substituted with deuterium, at least one of E 2  to E 4  is not hydrogen, 
     with the proviso that when E 1  is a substituted or unsubstituted C 1 -C 60  aryl group, Ar 1  has an asymmetric structure, 
     * and *′ each indicates a binding site to a neighboring atom, 
     R 1  to R 4 , R 11  to R 14 , R 20 , R 30 , and R 40  are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted CI-Coo alkoxy group, a substituted or unsubstituted C 1 -C 60  alkylthio group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 7 -C 60  alkyl aryl group, a substituted or unsubstituted C 7 -C 60  aryl alkyl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted C 2 -C 60  heteroaryl alkyl group, a substituted or unsubstituted C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —N(Q 1 )(Q 2 ), —Si(Q 3 )(Q 4 )(Q 5 ), —B(Q 6 )(Q 7 ), —P(Qs)(Q 9 ), or —P(═O)(Qs)(Q 9 ), 
     neighboring two or more of R 1  to R 4 , R 11  to R 14 , R 20 , R 30 , or R 40  are optionally linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group, 
     two or more of R 20  in the number of b20 are optionally be linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group, 
     two or more of R 30  in the number of b30 are optionally linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group, 
     two or more of R 40  in the number of b40 are optionally linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group, 
     b20, b30, and b40 are each independently 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, 
     when b20 is 2 or greater, two or more of R 20  are identical to or different from each other, when b30 is 2 or greater, two or more of R 30  are identical to or different from each other, and when b40 is 2 or greater, two or more of R 40  are identical to or different from each other. 
     at least one substituent of the substituted C 5 -C 30  carbocyclic group, the substituted C 1 -C 30  heterocyclic group, the substituted C 1 -C 60  alkyl group, the substituted C 2 -C 60  alkenyl group, the substituted C 2 -C 60  alkynyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 1 -C 60  alkylthio group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 1 -C 10  heterocycloalkyl group, the substituted C 3 -C 10  cycloalkenyl group, the substituted C 1 -C 10  heterocycloalkenyl group, the substituted C 6 -C 60  aryl group, the substituted C 7 -C 60  alkyl aryl group, the substituted C 7 -C 60  aryl alkyl group, the substituted C 6 -C 60  aryloxy group, the substituted C 6 -C 60  arylthio group, the substituted C 1 -C 60  heteroaryl group, the substituted C 2 -C 60  alkyl heteroaryl group, the substituted C 2 -C 60  heteroaryl alkyl group, the substituted C 1 -C 60  heteroaryloxy group, the substituted C 1 -C 60  heteroarylthio group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group is: 
     deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, or a C 1 -C 60  alkylthio group; 
     a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, or a C 1 -C 60  alkylthio group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q 11 )(Q 12 ), —Si(Q 13 )(Q 14 )(Q 15 ), —B(Q 16 )(Q 17 ), —P(Q 18 )(Q 19 ), —P(═O)(Q 18 )(Q 19 ), or a combination thereof; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one of deuterium, —F, —Cl, —Br, —SF 5 , —CD 3 , —CD 2 H, -CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 1 -C 60  alkylthio group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 7 -C 60  aryl alkyl group, a Ce-C 60  aryloxy group, a Ce-C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 2 -C 60  heteroaryl alkyl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q 21 )(Q 22 ), —Si(Q 23 )(Q 24 )(Q 25 ), —B(Q 26 )(Q 27 ), —P(Q 28 )(Q 29 ), —P(═O)(Q 28 )(Q 29 ), or a combination thereof; or 
     —N(Q 31 )(Q 32 ), —Si(Q 33 )(Q 34 )(Q 35 ), —B(Q 36 )(Q 37 ), —P(Q 38 )(Q 39 ), or —P(═O)(Q 38 )(Q 39 ), and 
     Q 1  to Q 9 , Q 11  to Q 19 , Q 21  to Q 29,  and Q 31  to Q 39  are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, —SF 5 , a hydroxyl group, a cyano group, a nitro group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 1 -C 60  alkylthio group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 7 -C 60  aryl alkyl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 2 -C 60  heteroaryl alkyl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group. 
     According to another aspect, provided is an organic light-emitting device including: a first electrode; a second electrode; and an organic layer located between the first electrode and the second electrode, wherein the organic layer includes an emission layer, and wherein the organic layer further inlcudes at least one of the organometallic compound. 
     The organometallic compound may be included in the emission layer of the organic layer, and the organometallic compound included in the emission layer may act as a dopant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The above and other aspects, features, and advantages of one or more exemplary embodiments will be more apparent from the following detailed description taken in conjunction with the FIGURE, which is a schematic cross-sectional view showing an organic light-emitting device according to one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     The terminology used herein is for the purpose of describing one or more exemplary embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “or” means “and/or.” It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present embodiments. 
     Exemplary embodiments are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present claims. 
     It will be understood that when an element is referred to as being “on” another element, it can be directly in contact with the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this general inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, 20%, 10%, 5% of the stated value. 
     Hereinafter, a work function or a highest occupied molecular orbital (HOMO) energy level is expressed as an absolute value from a vacuum level. In addition, when the work function or the HOMO energy level is referred to be “deep,” “high” or “large,” the work function or the HOMO energy level has a large absolute value based on “0 eV” of the vacuum level, while when the work function or the HOMO energy level is referred to be “shallow,” “low,” or “small,” the work function or HOMO energy level has a small absolute value based on “0 eV” of the vacuum level. 
     An aspect provides an organometallic compound represented by Formula 1: 
       M 1 (L 11 ) n11 (L 12 ) n12    Formula 1
 
     wherein, in Formula 1, M 1  may be a first-row transition metal of the Periodic Table of Elements, a second-row transition metal of the Periodic Table of Elements, or a third-row transition metal of the Periodic Table of Elements. 
     In one or more embodiments, M 1  in Formula 1 may be beryllium (Be), magnesium (Mg), aluminum (Al), calcium (Ca), titanium (Ti), manganese (Mn), cobalt (Co), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), zirconium (Zr), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), rhenium (Re), platinum (Pt), or gold (Au). 
     In one or more embodiments, M 1  may be Pd, Pt, or Au. 
     In one or more embodiments, M 1  in Formula 1 may be Pt or Pd. 
     In one or more embodiments, M 1  in Formula 1 may be Pt. 
     L 11  in Formula 1 is a ligand represented by Formula 1-1: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 1-1,  *1  to  *4  are each independently a binding site to M 1 . 
     Ring A 20  and ring A 30  in Formula 1 are each independently a C 5 -C 30  carbocyclic group or a C 1 -C 30  heterocyclic group. 
     In one or more embodiments, ring A 20  and ring A 30  may each independently be: 
     a phenyl group, a naphthalene group, an anthracene group, a phenanthrene group, a triphenylene group, a pyrene group, a chrysene group, a cyclopentadiene group, a 1,2,3,4-tetrahydronaphthalene group, a furan group, a thiophene group, a silole group, an indene group, a fluorene group, an indole group, a carbazole group, a benzofuran group, a dibenzofuran group, a benzothiophene group, a dibenzothiophene group, a benzosilole group, a dibenzosilole group, an azafluorene group, an azacarbazole group, an azadibenzofuran group, an azadibenzothiophene group, an azadibenzosilole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a phenanthroline group, a pyrrole group, a pyrazole group, an imidazole group, a triazole group, a tetrazole group, an oxazole group, an isoxazole group, a thiazole group, an isothiazole group, an oxadiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, an indazole group, a benzoxazole group, a benzothiazole group, a benzoxadiazole group, a benzothiadiazole group, a benzotriazole group, a diazaindene group, a triazaindene group, a 5,6,7,8-tetrahydroisoquinoline group, or a 5,6,7,8-tetrahydroquinoline group. 
     In one or more embodiments, A 40  may be a phenyl group, a naphthalene group, an anthracene group, a phenanthrene group, a triphenylene group, a pyrene group, a chrysene group, a cyclopentadiene group, a 1,2,3,4-tetrahydronaphthalene group, a fluorene group, a carbazole group, a benzofuran group, a dibenzofuran group, a benzothiophene group, a dibenzothiophene group, a benzosilole group, a dibenzosilole group, an azafluorene group, an azacarbazole group, an azadibenzofuran group, an azadibenzothiophene group, an azadibenzosilole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a phenanthroline group, a triazaindene group, a 5,6,7,8-tetrahydroisoquinoline group, or a 5,6,7,8-tetrahydroquinoline group. 
     In one or more embodiments, A 40  may be a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a phenanthroline group, a pyrrole group, an azafluorene group, an azacarbazole group, an azadibenzofuran group, an azadibenzothiophene group, an azadibenzosilole group, a 5,6,7,8-tetrahydroisoquinoline group, or a 5,6,7,8-tetrahydroquinoline group. 
     In one or more embodiments, ring A 20  may be a group represented by one of Formulae A 20 -1 to A 20 -13: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae A20-1 to A20-13, 
     X 20  is as described in the present specification, 
     Y 21  may be a single bond, O, S, N(R 26 ), C(R 26 )(R 27 ), or Si(R 26 )(R 27 ), 
     R 21  to R 29  are each independently as described in connection with R 20 , and 
     * indicates a binding site to Mi, and is the as described in connection with  *2 , 
     *′ and *″ each indicates a binding site to a neighboring atom. 
     In one or more embodiments, A 30  may be a group represented by one of Formulae A30-1 to A30-12: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae A30-1 to A30-12, 
     X 30  is as described in the present specification, 
     Y 31  may be a single bond, O, S, N(R 37 ), C(R 37 )(R 38 ), or Si(R 37 )(R 38 ), 
     R 31  to R 38  are each independently as described in connection with R 30 , and 
     * indicates a binding site to M 1 , and is as described in connection with  *3 , and 
     *′ and *″ each indicates a binding site to a neighboring atom. 
     In one or more embodiments, A 40  may be a group represented by one of Formulae A40-1 to A40-16: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae A40-1 to A40-16, 
     X 40  and R 40  are each as described in the present specification, 
     Y 41  may be a single bond, O, S, N(R 46 ), C(R 46 )(R 47 ), or Si(R 46 )(R 47 ), 
     R 41  to R 49  are each independently as described in connection with R 40 , and 
     * indicates a binding site to M 1 , as described in connection with  *4 , and 
       *1  indicates a binding site to a neighboring atom. 
     Ar 1  in Formula 1-1 is a group represented by Formula 2: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 2, E 1  is a C 1 -C 60  alkyl group substituted with deuterium, or a substituted or unsubstituted C 1 -C 60  aryl group. 
     * in Formula 2 indicates a binding site to a neighboring atom. 
     E 2  to E 5  in Formula 2 are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, —SF 5 , a hydroxyl group, a cyano group, a nitro group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 1 -C 60  alkylthio group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 7 -C 60  alkyl aryl group, a substituted or unsubstituted C 7 -C 60  aryl alkyl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted C 2 -C 60  heteroaryl alkyl group, a substituted or unsubstituted C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —N(Q 1 )(Q 2 ), —Si(Q 3 )(Q 4 )(Q 5 ), —B(Q 6 )(Q 7 ), —P(Q 8 )(Q 9 ), or —P(═O)(Q 8 )(Q 9 ), and 
     at least one of E 2  to E 5  is not hydrogen. 
     In Formula 2, when E 1  is a C 1 -C 60  alkyl group substituted with deuterium and E 5  is a C 1 -C 60  alkyl group substituted with deuterium, at least one of E 2  to E 4  is not hydrogen. 
     In Formula 2, when E 1  is a substituted or unsubstituted C 1 -C 60  aryl group, Ar 1  has an asymmetric structure. 
     In one or more embodiments, E 1  may be: 
     a C 1 -C 30  alkyl group substituted with deuterium; 
     a C 1 -C 60  aryl group; or 
     a C 1 -C 60  aryl group substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a C 1 -C 10  alkylthio group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, or a combination thereof. 
     In one or more embodiments, E 1  may be: 
     a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a neo-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, or a tert-decyl group, each substituted with at least one deuterium; 
     a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, or a chrysenyl group; or 
     a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, or a chrysenyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosporic acid grouop or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a C 1 -C 10  alkylthio group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cyclohepteny group, a phenyl group, a napthyl group, a pyridinyl group, a pyrimidinyl group, or a combination thereof. 
     hydrogen, deuterium, —F, —Cl, —Br, —I, or —SF 5 ; 
     a C 1 -C 30  alkyl group; 
     a C 1 -C 30  alkyl group substituted with at least one of deuterium, —F, —Cl, —Br, —I, —SF 5 , —CD 3 , —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a sald thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a C 1 -C 10  alkythio group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl, a phenyl group, a napthyl group, a pyridinyl group, a pyrimidinyl group, or a combination thereof; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a napthyl group, a a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a napthyl group, a fluorenyl group, a phenanthreny group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group,a furanyl group, an imidazolyl group, an pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl groupo, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group; or 
     a phenyl group, a napthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl groupk, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group,k a thiopheyl group, a furanyl group, a imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl groupk, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl groupm a quiinoxalinyl group, a quiinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl grouop, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopoyridinyl group, or an imidazopyrimidinyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —SF 5 , —CD 3 , —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a C 1 -C 10  alkythio group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a napthyl group, a pyridinyl grouop, a pyrimidinyl group, or a combination thereof. 
     In one or more embodiments, E 2  to E 5  may each independently be: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, —SF 5 a cyano group, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl grouip, a neo-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl grouop, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, a cyclopentyl group, a cyclohexyl group, a cyclohetyl group, a cyclooctyl goup, an adamanrtanyl group, a norbornanyl group, a norbornenyl group, a cyuclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinylo groupm, a quinoxalinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopoyridinyl group, or an imidazopyrimidinyl group; or 
     a methyl grouop, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a neo-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an issoctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, a n-decyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl grooup, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a C 1 -C 10  alkylthio group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, or a combination thereof. 
     In one or more embodiments, An may be a group represented by one of Formulae Ar 1 -1 to Ar 1 -14: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae Ar 1 -1 to Ar 1 -14, 
     E 11  may be a C 1 -C 60  alkyl group substituted with deuterium, or a substituted or unsubstituted C 1 -C 60  aryl group, 
     E 21  may be a C 1 -C 60  alkyl group substituted with deuterium, or a substituted or unsubstituted C 1 -C 60  aryl group, 
     E 21  and E 25  may be different from each other, 
     E 31  and E 35  may each independently be a C 1 -C 60  alkyl group substituted with deuterium, 
     E 12  to E 15 , E 22  to E 25 , and E 32  to E 34  may each independently be deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 1 -C 60  alkylthio group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 7 -C 60  alkyl aryl group, a substituted or unsubstituted C 7 -C 60  aryl alkyl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted C 2 -C 60  heteroaryl alkyl group, a substituted or unsubstituted C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —N(Q 1 )(Q 2 ), —Si(Q 3 )(Q 4 )(Q 5 ), —B(Q 6 )(Q 7 ), —P(Q 8 )(Q 9 ), or —P(═O)(Qs)(Q 9 ), and 
     * indicates a binding site to a neighboring atom. 
     In one or more embodiments, E 11 , E 21,  and E 31  in Formulae Ar 1 -1 to Ar 1 -14 are each independently as described in connection with E 1  in Formula 2. 
     In one or more embodiments, E 12  to E 15 , E 22  to E 25 , and E 32  to E 35  in Formulae Ar 1 -1 to Ar 1 -14 are each independently as described in connection with E 2  to E 5  in Formula 2. 
     In one or more embodiments, An may be a group represented by one of Formulae Ar 1 (1) to Ar 1 (104): 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae Ar 1  (1) to Ar 1 (104), 
     * indicates a binding site to a neighboring atom. 
     In one or more embodiments, Ar 1  may be a group having an asymmetric structure. As used herein, the term “asymmetric structure” means that the group Ar 1  includes substituent groups that are arranged in an asymmetric manner to provide asymmetry to the Ar 1  group. 
     R 1  to R 4 , R 11  to R 14 , R 20 , R 30 , and R 40  in Formula 1-1 are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 1 -C 60  alkylthio group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 7 -C 60  alkyl aryl group, a substituted or unsubstituted C 7 -C 60  aryl alkyl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted C 2 -C 60  heteroaryl alkyl group, a substituted or unsubstituted C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —N(Q 1 )(Q 2 ), —Si(Q 3 )(Q 4 )(Q 5 ), —B(Q 6 )(Q 7 ), —P(Qs)(Q 9 ), or —P(═O)(Qs)(Q 9 ), and 
     neighboring two or more of R 1  to R 4 , R 11  to R 14 , R 20 , R 30 , or R 40  are optionally linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group. 
     two or more of R 20  in the number of b20 are optionally linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group, 
     two or more of R 30  in the number of b30 are optionally linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group, 
     two or more of R 40  in the number of b40 are optionally linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group, 
     b20, b30, and b40 in Formula 1-1 are each independently 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, and 
     when b20 is 2 or greater, two or more of R 20  are identical to or different from each other, when b30 is 2 or greater, two or more of R 30  are identical to or different from each other, and when b40 is 2 or greater, two or more of R 40  are identical to or different from each other. 
     In one or more embodiments, R 1  to R 4 , R 11  to R 14 , R 20 , R 30 , and R 40  may each independently be: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, or a C 1 -C 2 o alkylthio group; 
     a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, or a C 1 -C 20  alkylthio group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CF H2, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, or a combination thereof; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkylthio group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, or a combination thereof; or 
     —N(Q 1 )(Q 2 ), —Si(Q 3 )(Q 4 )(Q 5 ), —B(Q 6 )(Q 7 ), —P(Q 8 )(Q 9 ), or —P(═O)(Q 8 )(Q 9 ), and Q 1  to Q 9  may each independently be: 
     —CH 3 , —CD 3 , —CD 2 H, —CDH 2 , —CH 2 CH 3 , —CH 2 CD 3 , —CH 2 CD 2 H, —CH 2 CDH 2 , —CHDCH 3 , —CHDCD 2 H, —CHDCDH 2 , —CHDCD 3 , —CD 2 CD 3 , —CD 2 CD 2 H, or —CD 2 CDH 2 ; 
     an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a phenyl group, or a naphthyl group; or 
     an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a phenyl group, or a naphthyl group, each substituted with deuterium, a C 1 -C 10  alkyl group, a phenyl group, or a combination thereof. 
     In one or more embodiments, R 1  to R 4 , R 10 , R 20 , R 30 , and R 40  may each independently be hydrogen, deuterium, —F, a cyano group, a nitro group, —SF 5 , —CH 3 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a group represented by one of Formulae 9-1 to 9-61, or a group represented by one of Formulae 10-1 to 10-359: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 9-1 to 9-61 and 10-1 to 10-359, * indicates a binding site to a neighboring atom, “Ph” indicates a phenyl group, “TMS” indicates a trimethylsilyl group, and “TMG” indicates a trimethylgermyl group. 
     When b10 is 2, two of Rio may be identical to or different from each other, and when b20 is 2 or more, two or more of R 20  may be identical to each other or different from each other. 
     In Formula 1-1, two or more of a plurality of R 10 ; two or more of a plurality of R 2 o; or neighboring two or more of R 10 , R 20  to R 22 , or R 31  to R 37  are optionally linked together to form a substituted or unsubstituted C 5 -C 30  carbocyclic group or a substituted or unsubstituted C 1 -C 30  heterocyclic group. 
     In one or more embodiments, two or more of a plurality of Rio; two or more of a plurality of R 20 ; or neighboring two or more of R 10 , R 20  to R 22 , or R 31  to R 37  may optionally be linked together via a single bond, a double bond, or a first linking group to form a C 5 -C 30  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 30  heterocyclic group unsubstituted or substituted with at least one R 10a  (for example, a fluorene group, a xanthene group, or an acridine group, each unsubstituted or substituted with at least one R 10a ). R 10a  is as described in connection with R 10 . 
     The first linking group may be *—N(R 8 )—*′, *—B(R 8 )—*′, *—P(R 8 )—*′, *—C(R 8 )(R 9 )—*′, *—Si(R 8 )(R 9 )—*′, *—Ge(R 8 )(R 9 )—*′, *—Se—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O)2-* I , *—C(R 8 )═*′, *═C(R 8 )—*′, *—C(R 8 )═C(R 9 )—*′, *—C(═S)—*′, or *—C□C—*′, R 8  and R 9  are each as described in connection with R 10 , and each of * and *′ indicates a binding site to a neighboring atom. 
     In one or more embodiments, Q 1  to Q 9 , Q 11  to Q 19 , Q 21  to Q 29  and Q 31  to Q 39  described herein may each independently be: 
     deuterium, —CH 3 , —CD 3 , —CD 2 H, —CDH 2 , —CH2CH 3 , —CH2CD 3 , —CH2CD 2 H, —CH 2 CDH 2 , —CHDCH 3 , —CHDCD 2 H, —CHDCDH 2 , —CHDCD 3 , —CD 2 CD 3 , —CD 2 CD 2 H, or —CD 2 CDH 2 ; 
     an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a phenyl group, or a naphthyl group; or 
     an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a neo-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a phenyl group, or a naphthyl group, each substituted with at least one of deuterium, a C 1 -C 10  alkyl group, a phenyl group, or a combination thereof. 
     In one or more embodiments, the organometallic compound represented by Formula 1 may be represented by Formula 11: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 11, 
     M 1 , Ar 1 , T 1 , and R 11  to R 14  are respectively as those described in the present specification, 
     R 21  to R 23  are each independently as described in connection with R 20 , 
     R 31  to R 36  are each independently as described in connection with R 30 , and 
     R 41  to R 44  are each independently as described in connection with R 40.    
     In Formula 1-1, X 20  is C or N, X 21  is C or N, and X 22  is C or N. 
     In Formula 1-1, X 30  is C or N, X 31  is C or N, and X 32  is C or N. 
     In Formula 1-1, X 40  is C or N, and X 41  is C or N. 
     For example, X 20  may be C. In one or more embodiments, X 20  may be N. 
     For example, X 30  may be C. In one or more embodiments, X 30  may be N. 
     For example, X 40  may be C. In one or more embodiments, X 40  may be N. 
     In Formula 1-1, X 20  is C or N, X 21  is C or N, X 22  is C or N, X 31  is C or N, X 32  is C or N, and X 41  is C or N. 
     For example, X 21  may be C. In one or more embodiments, X 21  may be N. 
     For example, X 22  may be C. In one or more embodiments, X 22  may be N. 
     For example, X 31  may be C. In one or more embodiments, X 31  may be N. 
     For example, X 32  may be C. In one or more embodiments, X 32  may be N. 
     For example, X 41  may be C. In one or more embodiments, X 41  may be N. 
     In Formula 1-1, a bond between M 1  and a moiety represented by 
     
       
         
         
             
             
         
       
     
     a bond between M 1  and ring A 20 , 
     a bond between M 1  and ring A 30 , and 
     a bond between M 1  and ring A 40  may each independently be a covalent bond or a coordinate bond. 
     In one or more embodiments, two bonds of 
     a bond between M 1  and 
     
       
         
         
             
             
         
       
     
     a bond between M 1  and ring A 20 , 
     a bond between M 1  and ring A 30 , and 
     a bond between M 1  and ring A 40  may each be a covalent bond, and the other two bonds may each be a coordinate bond. 
     In one or more embodiments, 
     a bond between M 1  and may be a coordinate bond, 
     
       
         
         
             
             
         
       
     
     a bond between M 1  and ring A 20  may be a covalent bond, 
     a bond between M 1  and ring A 30  may be a covalent bond, and 
     a bond between M 1  and ring A 40  may be a coordinate bond. 
     In one or more embodiments, the organometallic compound may be electrically neutral. 
     L 12  in Formula 1 may be a monodentate ligand or a bidentate ligand. 
     For example, L 12  in Formula 1 may be a ligand represented by one of Formulae 7-1 to 7-11, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 7-1 to 7-11, 
     ring A 71  and ring A 72  may each independently be a C 5 -C 20  carbocyclic group or a C 1 -C 20  heterocyclic group, 
     X 71  and X 72  may each independently be C or N, 
     X 73  may be N or C(Q 73 ), X 74  may be N or C(Q 74 ), X 75  may be N or C(Q 75 ), X 76  may be N or C(Q 76 ), and X 77  may be N or C(Q 77 ), 
     X 78  may be O, S, or N(Q 78 ), and X 79  may be O, S, or N(Q 79 ), 
     Y 71  and Y 72  may each independently be a single bond, a double bond, a substituted or unsubstituted C 1 -C 5  alkylene group, a substituted or unsubstituted C 2 -C 5  alkenylene group, or a substituted or unsubstituted C 6 -C 10  arylene group, 
     Z 71  and Z 72  may each independently be N, O, N(R 74 ), P(R 75 )(R 76 ), or AS(R 75 )(R 76 ), 
     Z 73  may be P or As, 
     Z 74  may be CO or CH 2 , 
     R 71  to R 80  and Q 73  to Q 79  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, —SF 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, a phosphoric acid or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 1 -C 60  alkylthio group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 7 -C 60  alkyl aryl group, a substituted or unsubstituted C 7 -C 60  aryl alkyl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted C 2 -C 60  heteroaryl alkyl group, a substituted or unsubstituted C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, or a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, wherein R 71  and R 72  may optionally be linked together to form a ring, R 77  and R 78  may optionally be linked together to form a ring, R 78  and R 79  may optionally be linked together to form a ring, and R 79  and R 80  may optionally be linked together to form a ring, 
     b71 and b72 may each independently be 1, 2, or 3, and 
     * and *′ each indicate a binding site to Mi. 
     For example, A 71  and A 72  in Formula 7-1 may each independently be a phenyl group, a naphthalene group, an imidazole group, a benzimidazole group, a pyridine group, a pyrimidine group, a triazine group, a quinoline group, or an isoquinoline group, but embodiments are not limited thereto. 
     For example, X 72  and X 79  in Formula 7-1 may each be N, but embodiments are not limited thereto. 
     For example, in Formula 7-7, X 73  may be C(Q 73 ), X 74  may be C(Q 74 ), X 75  may be C(Q 75 ), X 76  may be C(Q 76 ), and X 77  may be C(Q 77 ), but embodiments are not limited thereto. 
     For example, in Formula 7-8, X 78  may be N(Q 78 ), and X 79  may be N(Q 79 ), but embodiments are not limited thereto. 
     For example, Y 71  and Y 72  in Formulae 7-2, 7-3, and 7-8 may each independently be a substituted or unsubstituted methylene group or a substituted or unsubstituted phenylene group, but embodiments are not limited thereto. 
     For example, Z 71  and Z 72  in Formulae 7-1 and 7-2 may each be 0, but embodiments are not limited thereto. 
     For example, Z 73  in Formula 7-4 may be P, but embodiments are not limited thereto. 
     For example, R 71  to Rgo and Q 73  to Q 79  in Formulae 7-1 to 7-11 may each independently be: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, —Sb 5 , a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, or a C 1 -C 20  alkylthio group; 
     a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, or a C 1 -C 20  alkylthio group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptanyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a biphenyl group, a (C 1 -C 20  alkyl)phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, or a combination thereof; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptanyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a biphenyl group, a C 1 -C 20  alkylphenyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl groouop, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopoyridinyl group, or an imidazopyrimidinyl group; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptanyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a biphenyl group, an anthracenyl group, a fluoranthenyl group, a fluorenyl group, a phenznthrenlyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkylthio group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptanyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a biphenyl group, a C 1 -C 20  alkylphenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, —Si(Q 11 )(Q 12 )(Q 13 ), —B(Q 11 )(Q 12 ), —N(Q 11 )(Q 12 ), or a combination thereof; or 
     —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), or —N(Q 1 )(Q 2 ), and 
     Q 1  to Q 3  and Q 11  to Q 13  may each independently be: 
     a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a 2-methylbutyl group, a sec-pentyl group, a tert-pentyl group, a neo-pentyl group, a 3-pentyl group, a 3-methyl-2-butyl group, a phenyl group, a biphenyl group, a C 1 -C 20  alkylphenyl group, or a naphthyl group; or 
     a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a 2-methylbutyl group, a sec-pentyl group, a tert-pentyl group, a neo-pentyl group, a 3-pentyl group, a 3-methyl-2-butyl group, a phenyl group, or a naphthyl group, each substituted with deuterium, a phenyl group, or a combination thereof, but embodiments are not limited thereto. 
     L 12  in Formula 1 may be a ligand represented by one of Formulae 5-1 to 5-116 or Formulae 8-1 to 8-23, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 5-1 to 5-116 and 8-1 to 8-23, 
     R 51  to R 53  may each independently be: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, —Sb 5 , a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, or a C 1 -C 20  alkythio group; 
     a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, or a C 1 -C 20  alkythio group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —SF 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an aminidino group, a hydrazine group, a hydrazone group, a carboxylic acid groupo or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptanyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a biphenyl group, a C 1 -C 20  alkylphenyl group, a napthyl group, a pyridinyl a phenyl group, a biphenyl group, a C 1 -C 20  alkylphenyl group, a napthyl group, a pyridinyl group, a pyrimidinyl group, or a combination thereof. 
     a cyclopentyl group, a cyclohexyl grouop, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptanyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl grouop, a cycloheptenyl group, a phenyl group, a biphenyl group, a (C 1 -C 20  alkyl)phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, a chrysenyl group, a pyrrolyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, a oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinolinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzofuranyl group, isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, s dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptanyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a biphenyl group, a (C 1 -C 20  alkyl)phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl groupo, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, an benzoquinolinyl group, a quinoxalinyl group, a quinazolingl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl grooup, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group, each substitued with at least one of deuterium, —F, —Cl, —Br, —Im —SF 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkythio group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptanyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a biphenyl group, a (C 1 -C 20  alkyl)phenyl group, a napthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluorantheyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl gropu, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, —Si(Q 11 )(Q 12 )(Q 13 ), —B(Q 11 )(Q 12 ), —N(Q 11 )(Q 12 ), or a combination thereof; or 
     —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), or —N(Q 1 )(Q 2 ), 
     Q 1  to Q 3  and Q 11  to Q 13  may each independently be: 
     a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a 2-methylbutyl group, a sec-pentyl group, a tert-pentyl group, a neo-pentyl group, a 3-pentyl group, a 3-methyl-2-butyl group, a phenyl group, a biphenyl group, a C 1 -C 20  alkylphenyl group, or a naphthyl group; or 
     a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a 2-methylbutyl group, a sec-pentyl group, a tert-pentyl group, a neo-pentyl group, a 3-pentyl group, a 3-methyl-2-butyl group, a phenyl group, or a naphthyl group, each substituted with at least one of deuterium, a phenyl group, or a combination thereof, 
     b51 and b54 may each independently be 1 or 2, 
     b53 and b55 may each independently be 1, 2, or 3, 
     b52 may be 1, 2, 3, or 4, 
     “Ph” represents a phenyl group, 
     “Ph-d5” represents a phenyl group wherein five hydrogen atoms on the phenyl group are substituted with deuterium, and 
     * and *′ each indicate a binding site to M 1 . 
     In Formula 1, n11 is 1, and n12 is 0, 1, or 2. 
     In one or more embodiments, in Formula 1, M 1  may be Pt, n11 may be 1, and n12 may be 0, but embodiments are not limited thereto. 
     In one or more embodiments, the organometallic compound may be represented by one of Compounds 1 to 229: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The organometallic compound represented by Formula 1 may satisfy the structure of Formula 1 described above, and a moiety represented by 
     
       
         
         
             
             
         
       
     
     in the Lii ligand represented by Formula 1-1 may include Ari which is a phenyl group substituted with a specific substituent. Without wishing to be bound to theory, due to such a structure, the organometallic compound may have improved photochemical stability, and may be suitable for deep blue light emission. Accordingly, an electronic device, for example, an organic light-emitting device, using the organometallic compound represented by Formula 1 may exhibit excellent luminescence efficiency, lifespan, and color purity. 
     Although not limited by a specific theory, the electron donating characteristics of Lii ligand may be enhanced by Ari, and thus, the charge transfer may be improved, thereby improving the structural stability of the organometallic compound. Accordingly, by using the organometallic compound, the efficiency and lifespan of an organic light-emitting device may be improved. 
     The highest occupied molecular orbital (HOMO) energy level, lowest unoccupied molecular orbital (LUMO) energy level, energy gap, the lowest excitation triplet (T 1 ) energy level, and the lowest excitation singlet (S 1 ) energy levels of the organometallic compound represented by Formula 1 were evaluated using a density functional theory (DFT) method of the Gaussian 09 program with the molecular structure optimization obtained at the B3LYP level, and results thereof are shown in Table 1. The energy levels are expressed in electron volts (eV). 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Compound 
                 HOMO (eV) 
                 LUMO (eV) 
                 T 1  (eV) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Compound 1 
                 −4.69 
                 −1.23 
                 2.68 
               
               
                 Compound 2 
                 −4.64 
                 −1.19 
                 2.65 
               
               
                 Compound 3 
                 −4.80 
                 −1.33 
                 2.67 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1, it was confirmed that the organometallic compound represented by Formula 1 has suitable electrical characteristics for use as a dopant in an electronic device, for example, an organic light-emitting device. 
     In one or more embodiments, the full width at half maximum (FWHM) of an emission peak of an emission spectrum or an electroluminescence (EL) spectrum of the organometallic compound may be about 75 nanometers (nm) or less. For example, the FWHM of the emission peak of the emission spectrum or the EL spectrum of the organometallic compound may be in a range of about 30 nm to about 75 nm, about 40 nm to about 70 nm, or about 45 nm to about 60 nm. 
     In one or more embodiments, a maximum emission wavelength (also referred to as an emission peak wavelength, Amax) of the emission peak of the emission spectrum or the EL spectrum of the organometallic compound may be in a range of about 410 nm to about 490 nm. 
     Synthesis methods of the organometallic compound represented by Formula 1 may be recognizable by one of ordinary skill in the art and by referring to Synthesis Examples described herein. 
     Accordingly, the organometallic compound represented by Formula 1 may be suitable for use as a dopant in an organic layer, for example, an emission layer, of an organic light-emitting device. Thus, another aspect provides an organic light-emitting device including: a first electrode; a second electrode; and an organic layer that is located between the first electrode and the second electrode, wherein the organic layer includes an emission layer, and wherein the organic layer further includes at least one organometallic compound represented by Formula 1. 
     Since the organic light-emitting device includes the organic layer including the organometallic compound represented by Formula 1 as described above, excellent characteristics in terms of driving voltage, current efficiency, external quantum efficiency, roll-off ratio, and lifespan, and relatively narrow FWHM of the emission peak of the EL spectrum may be exhibited. 
     The organometallic compound represented by Formula 1 may be used between a pair of electrodes of an organic light-emitting device. For example, the organometallic compound represented by Formula 1 may be included in the emission layer. In this regard, the organometallic compound may act as a dopant, and the emission layer may further include a host (that is, an amount of the organometallic compound represented by Formula 1 in the emission layer is smaller than an amount of the host). 
     In one or more embodiments, the emission layer may emit blue light. For example, the emission layer may emit blue light having a maximum emission wavelength in a range of about 410 nm to about 490 nm. 
     The expression “(an organic layer) includes at least one of organometallic compounds” used herein may include a case in which “(an organic layer) includes identical organometallic compounds represented by Formula 1” and a case in which “(an organic layer) includes two or more different organometallic compounds represented by Formula 1.” 
     For example, the organic layer may include, as the organometallic compound, only Compound 1. In this regard, Compound 1 may be included in the emission layer of the organic light-emitting device. In one or more embodiments, the organic layer may include, as the organometallic compound, Compound 1 and Compound 2. In this regard, Compound 1 and Compound 2 may be present in an identical layer (for example, both Compound 1 and Compound 2 may be present in the same emission layer). 
     The first electrode may be an anode, which is a hole injection electrode, and the second electrode may be a cathode, which is an electron injection electrode. Alternatively, the first electrode may be a cathode, which is an electron injection electrode, and the second electrode may be an anode, which is a hole injection electrode. 
     For example, in the organic light-emitting device, the first electrode may be an anode, the second electrode may be a cathode, and the organic layer may further include a hole transport region between the first electrode and the emission layer and an electron transport region between the emission layer and the second electrode, wherein the hole transport region may include a hole injection layer, a hole transport layer, an electron blocking layer, a buffer layer, or a combination thereof, and the electron transport region may include a hole blocking layer, an electron transport layer, an electron injection layer, or a combination thereof. 
     The term “organic layer” used herein refers to a single layer and/or a plurality of layers located between the first electrode and the second electrode of the organic light-emitting device. The “organic layer” may include, in addition to an organic compound, an organometallic complex including a metal. 
     The FIGURE is a schematic cross-sectional view of an organic light-emitting device  10  according to one or more embodiments. Hereinafter, the structure and manufacturing method of the organic light-emitting device  10  according to one or more embodiments will be described in connection with the FIGURE. The organic light-emitting device  10  includes a first electrode  11 , an organic layer  15 , and a second electrode  19 , which are sequentially stacked. 
     A substrate may be additionally located under the first electrode  11  or on the second electrode 19. For use as the substrate, any substrate that is used in organic light-emitting devices and including those available in the art may be used, and for example, a glass substrate or a transparent plastic substrate, each having excellent mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and/or water resistance, may be used. 
     The first electrode  11  may be produced by depositing or sputtering, onto the substrate, a material for forming the first electrode  11 . The first electrode  11  may be an anode. The material for forming the first electrode  11  may be selected from materials with a high work function for easy hole injection. The first electrode  11  may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. The material for forming the first electrode  11  may be at least one of indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO 2 ), or zinc oxide (ZnO). In one or more embodiments, the material for forming the first electrode  11  may be metal, such as at least one of magnesium (Mg), aluminum (Al), silver (Ag), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), or magnesium-silver (Mg—Ag). 
     The first electrode  11  may have a single-layered structure or a multi-layered structure including a plurality of layers. For example, the first electrode  11  may have a three-layered structure of ITO/Ag/ITO, but embodiments are not limited thereto. 
     The organic layer  15  may be located on the first electrode  11 . 
     The organic layer  15  may include a hole transport region, an emission layer, and an electron transport region. 
     The hole transport region may be located between the first electrode  11  and the emission layer. 
     The hole transport region may include a hole injection layer, a hole transport layer, an electron blocking layer, a buffer layer, or a combination thereof. 
     The hole transport region may include only either a hole injection layer or a hole transport layer. In one or more embodiments, the hole transport region may have a hole injection layer/hole transport layer structure or a hole injection layer/hole transport layer/electron blocking layer structure, wherein, for each structure, respective layers are sequentially stacked in this stated order from the first electrode  11 . 
     When the hole transport region includes a hole injection layer, the hole injection layer may be formed on the first electrode  11  by using one or more suitable methods, for example, vacuum deposition, spin coating, casting, and/or Langmuir-Blodgett (LB) deposition. 
     When a hole injection layer is formed by vacuum deposition, the deposition conditions may vary according to a material that is used to form the hole injection layer, and the structure and thermal characteristics of the hole injection layer. For example, the deposition conditions may include a deposition temperature of about 100° C. to about 500° C., a vacuum pressure of about 10 −8  torr to about 10 −3  torr, and a deposition rate of about 0.01 angstroms per second (Å/sec) to about 100 Å/sec, but embodiments are not limited thereto. 
     When the hole injection layer is formed using spin coating, coating conditions may vary according to the material used to form the hole injection layer, and the structure and thermal properties of the hole injection layer. For example, a coating speed may be from about 2,000 revolutions per minute (rpm) to about 5,000 rpm, and a temperature at which a heat treatment is performed to remove a solvent after coating may be from about 80° C. to about 200° C., but embodiments are not limited thereto. 
     Conditions for forming the hole transport layer and the electron blocking layer may respectively be as the conditions for forming the hole injection layer. 
     The hole transport region may include at least one of 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (TDATA), 4,4′,4″-tris{N-(2-naphthyl)-N-phenylamino}-triphenylamine (2-TNATA) N,N′-di(1-naphthyl)-N,N′-diphenyibenzidine (NPB), β-NPB, N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1-biphenyl]-4,4′-diamine (TPD), spiro-TPD, spiro-NPB, methylated NPB, 4,4′-cyclohexylidene bis[N,N-bis(4-methylphenyl)benzenamine] (TAPC), 4,4′-bis[N, N′-(3-tolyl)amino]-3,3′-dimethylbiphenyl (HMTPD), 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA), poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), polyaniline/camphor sulfonic acid (PANI/CSA), (polyaniline)/poly(4-styrenesulfonate) (PANI/PSS), a compound represented by Formula 201, or a compound represented by Formula 202: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     wherein, in Formula 201, Ar 101  and Ar 102  may each independently be: 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an acenaphthylene group, a fluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, or a pentacenylene group; or 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an acenaphthylene group, a fluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, or a pentacenylene group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 1 -C 60  alkylthio group, a C 3 -C 10  cycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 69  aryl group, a C 7 -C 60  alkyl aryl group, a C 7 -C 60  aryl alkyl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 2 -C 60  heteroaryl alkyl group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group. 
     In Formula 201, xa and xb may each independently be an integer from 0 to 5, or may each independently be 0, 1, or 2. For example, xa may be 1, and xb may be 0, but embodiments are not limited thereto. 
     R 101  to R 108,  R 111  to R 119,  and R 121  to R 124  in Formulae 201 and 202 may each independently be: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group (for example, a methyl group, an ethyl group, a propyl group, a butyl group, pentyl group, a hexyl group, etc.), a C 1 -C 10  alkoxy group (for example, a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, etc.), or a C 1 -C 10  alkylthio group; 
     a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, or a C 1 -C 10  alkylthio group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof; or a combination thereof, 
     a phenyl group, a naphthyl group, an anthracenyl group, a fluorenyl group, or a pyrenyl group; or 
     a phenyl group, a naphthyl group, an anthracenyl group, a fluorenyl group, or a pyrenyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a C 1 -C 10  alkylthio group, or a combination thereof, 
     but embodiments are not limited thereto. 
     R 109  in Formula 201 may be: 
     a phenyl group, a naphthyl group, an anthracenyl group, or a pyridinyl group; or 
     a phenyl group, a naphthyl group, an anthracenyl group, or a pyridinyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, a phosphoric acid or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkylthio group, a phenyl group, a naphthyl group, an anthracenyl group, or a pyridinyl group. 
     In one or more embodiments, the compound represented by Formula 201 may be represented by Formula 201A, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 201A, R 101 , R 111 , R 112 , and R 109  are respectively as those described herein. 
     For example, the compounds represented by Formulae 201 and 202 may include one or more of Compounds HT1 to HT20, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the hole transport region may be in a range of about 100 angstroms (Å) to about 10,000 Å, for example, about 100 Å to about 1,000 Å. When the hole transport region includes at least one of a hole injection layer and a hole transport layer, a thickness of the hole injection layer may be in a range of about 100 Å to about 10,000 Å, for example, about 100 Å to about 1,000 Å, and a thickness of the hole transport layer may be in a range of about 50 Å about 2,000 Å, for example, about 100 Å to about 1,500 Å. When the thicknesses of the hole transport region, the hole injection layer, and the hole transport layer are within these ranges, satisfactory hole transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The hole transport region may further include, in addition to the materials as described above, a charge-generation material for improving conductive properties. The charge-generation material may be homogeneously or non-homogeneously dispersed in the hole transport region. 
     The charge-generation material may be, for example, a p-dopant. The p-dopant may be one of a quinone derivative, a metal oxide, or a cyano group-containing compound, but embodiments are not limited thereto. For example, non-limiting examples of the p-dopant include: a quinone derivative, such as tetracyanoquinodimethane (TCNQ), 2,3,5,6-tetrafluoro-tetracyano-1,4-benzoquinonedimethane (F4-TCNQ), or F6-TCNNQ; a etal oxide, such as a tungsten oxide or a molybdenum oxide; or a compound containing a cyano group, such as Compound HT-D1 or Compound F12, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
     
     The hole transport region may further include a buffer layer. 
     The buffer layer may compensate for an optical resonance distance according to a wavelength of light emitted from the emission layer, and thus, efficiency of the light-emitting device may be improved. 
     An emission layer may be formed on the hole transport region by using one or more suitable methods, such as vacuum deposition, spin coating, casting, or LB deposition. When the emission layer is formed by vacuum deposition or spin coating, the deposition or coating conditions may be similar to those applied in forming the hole injection layer, though the deposition or coating conditions may vary according to a material that is used. 
     Meanwhile, when the hole transport region includes an electron blocking layer, a material for forming the electron blocking layer may be selected from materials for the hole transport region described above and host materials to be described below, but embodiments are not limited thereto. For example, when the hole transport region includes an electron blocking layer, the material for forming the electron blocking layer may be mCP, which will be described below. 
     The emission layer may include a host and a dopant, and the dopant may include the organometallic compound represented by Formula 1. 
     The host may include at least one selected from 1,3,5-tri(1-phenyl-1H-benzo[d]im idazol-2-yl)phenyl (TPBi), 3-tert-butyl-9,10-di(naphth-2-yl)anthracene (TBADN), 9,10-di(naphthalene-2-yl)anthracene (ADN) (also referred to as “DNA”), 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), 4,4′-bis(9-carbazolyl)-2,2′-dimethyl-biphenyl (CDBP), 1,3,5-tris(carbazole-9-yl)benzene (TCP), 1,3-bis(N-carbazolyl)benzene (mCP), Compound H50, or Compound H51: 
     
       
         
         
             
             
         
       
     
     In one or more embodiments, the host may include a compound represented by Formula 301: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 301, Ar 111  and Ar 112  may each independently be: 
     a phenylene group, a naphthylene group, a phenanthrenylene group, or a pyrenylene group; or 
     a phenylene group, a naphthylene group, a phenanthrenylene group, or a pyrenylene group, each substituted with at least one of a phenyl group, a naphthyl group, an anthracenyl group, or a combination thereof. 
     Ar 113  to Ar 116  in Formula 301 may each independently be: 
     a C 1 -C 10  alkyl group, a phenyl group, a naphthyl group, a phenanthrenyl group, or a pyrenyl group; or 
     a phenyl group, a naphthyl group, a phenanthrenyl group, or a pyrenyl group, each substituted with at least one of a phenyl group, a naphthyl group, an anthracenyl group, or a combination thereof. 
     g, h, i, and j in Formula 301 may each independently be an integer from 0 to 4, and may be, for example, 0, 1, or 2. 
     Ar 113  and Ar 116  in Formula 301 may each independently be: 
     a C 1 -C 10  alkyl group substituted with at least one of a phenyl group, a naphthyl group, an anthracenyl group, or a combination thereof; 
     a phenyl group, a naphthyl group, an anthracenyl group, a pyrenyl group, a phenanthrenyl group, or a fluorenyl group; 
     a phenyl group, a naphthyl group, an anthracenyl group, a pyrenyl group, a phenanthrenyl group, or a fluorenyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 1 -C 60  alkylthio group, a phenyl group, a naphthyl group, an anthracenyl group, a pyrenyl group, a phenanthrenyl group, a fluorenyl group, or a combination thereof; or a group represented by formula: 
     
       
         
         
             
             
         
       
     
     but embodiments are not limited thereto. 
     In one or more embodiments, the host may include a compound represented by Formula 302: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 302, Ar 122  to Ar 125  are each as described in connection with Ar 113  in Formula 301. 
     Ar 126  and Ar 127  in Formula 302 may each independently be a C 1 -C 10  alkyl group (for example, a methyl group, an ethyl group, or a propyl group). 
     k and l in Formula 302 may each independently be an integer from 0 to 4. For example, k and l may each be 0, 1, or 2. 
     When the organic light-emitting device 10 is a full-color organic light-emitting device 10, the emission layer may be patterned into a red emission layer, a green emission layer, and a blue emission layer. In one or more embodiments, due to a stacked structure including a red emission layer, a green emission layer, and/or a blue emission layer, the emission layer may emit white light, and various modifications are possible. 
     When the emission layer includes a host and a dopant, an amount of the dopant may be in a range of about 0.01 part by weight to about 15 parts by weight based on 100 parts by weight of the host, but embodiments are not limited thereto. 
     In one or more embodiments, the organic layer in organic light-emitting device may further include, in addition to the organometallic compound represented by Formula 1, a fluorescent dopant. 
     For example, the fluorescent dopant may be a condensed polycyclic compound, a styryl-based compound, or a combination thereof. 
     For example, the fluorescent dopant may include a naphthalene-containing core, a fluorene-containing core, a spiro-bifluorene-containing core, a benzofluorene-containing core, a dibenzofluorene-containing core, a phenanthrene-containing core, an anthracene-containing core, a fluoranthene-containing core, a triphenylene-containing core, a pyrene-containing core, a chrysene-containing core, a naphthacene-containing core, a picene-containing core, a perylene-containing core, a pentaphene-containing core, an indenoanthracene-containing core, a tetracene-containing core, a bisanthracene-containing core, or one of cores represented by Formulae 501-1 to 501-18, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the fluorescent dopant may be a styryl-amine-containing compound, a styryl-carbazole-containing compound, or a combination thereof, but embodiments are not limited thereto. 
     In one or more embodiments, the fluorescent dopant may be a compound represented by Formula 501: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 501, 
     Ar 501  may be: 
     a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a tetracene group, a bisanthracene group, or a group represented by one of Formulae 501-1 to 501-18; or 
     a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a tetracene group, a bisanthracene group, or a group represented by one of Formulae 501-1 to 501-18, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 1 -C 60  alkylthio group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 7 -C 60  aryl alkyl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 2 -C 60  heteroaryl alkyl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, or -Si(Q 5 oi)(Q 502 )(Q 503 ), 
     wherein Q 501  to Q 503  may each independently be hydrogen, a C 1 -C 60  alkyl group, a C 1 -C 60  alkoxy group, a C 1 -C 60  alkylthio group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 7 -C 60  aryl alkyl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 2 -C 60  heteroaryl alkyl group, a C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group, or a combination thereof, 
     L 501  to L 503  may each independently be a substituted or unsubstituted C 3 -C 10  cycloalkylene group, a substituted or unsubstituted heterocycloalkylene group, a substituted or unsubstituted C 3 -C 10  cycloalkenylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenylene group, a substituted or unsubstituted C 6 -C 60  arylene group, a substituted or unsubstituted C 1 -C 60  heteroarylene group, a substituted or unsubstituted divalent non-aromatic condensed polycyclic group, or a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group, 
     R 501  and R 502  may each independently be: 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazole group, a triazinyl group, a dibenzofuranyl group, or a dibenzothiophenyl group; or 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, or a dibenzothiophenyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —SF 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkylthio group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, or a combination thereof, 
     xd1 to xd3 may each independently be 0, 1, 2, or 3, and 
     xd4 may be 0, 1, 2, 3, 4, 5, or 6. 
     For example, in Formula 501, 
     Ar 501  may be: 
     a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a tetracene group, a bisanthracene group, or a group represented by one of Formulae 501-1 to 501-18; or 
     a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a tetracene group, a bisanthracene group, or a group represented by one of Formulae 501-1 to 501-18, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkylthio group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a carbazolyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, or —Si(Q 501 )(Q 502 )(Q 503 ), 
     wherein Q 501  to Q 503  may each independently be hydrogen, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkylthio group, a phenyl group, a biphenyl group, a terphenyl group or a naphthyl group, or a combination thereof, 
     L 501  to L 503  are each as described in connection with L 21 , 
     xd1 to xd3 may be each independently 0, 1, or 2, and 
     xd4 may be 0, 1, 2, or 3, but embodiments are not limited thereto. 
     In one or more embodiments, the fluorescent dopant may include a compound represented by one of Formulae 502-1 to 502-5: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 502-1 to 502-5, 
     X 51  may be N or C-[(L 501 ) xd1 -R 501 ], X 52  may be N or C-[(L 502 ) xd2 -R 502 ], X 53  may be N or C-[(L 503 ) xd3 -R 503 ], X 54  may be N or C-[(L 504 ) xd4 -R 504 ], X 55  may be N or C-[(L 505 ) xd5 -R 505 ], X 56  may be N or C-[(L 506 ) xd6 -R 506 ], X 57  may be N or C-[(L 507 ) xd7 -R 507 ], and X 58  may be N or C-[(L 508 ) xd8 -R 508 ], 
     L 501  to L 508  are each as described in connection with L 501  in Formula 501, 
     xd1 to xd8 are each as described in connection with xd1 in Formula 501, 
     R 501  to R 508  may each independently be: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, or a C 1 -C 20  alkylthio group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazole group, a triazinyl group, a dibenzofuranyl group, or a dibenzothiophenyl group; or 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, or a dibenzothiophenyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkylthio group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, or a combination thereof, 
     xd11 and xd12 may each independently be 0, 1, 2, 3, 4, or 5, 
     two of R 501  to R 504  may optionally be linked together to form a saturated or unsaturated ring, and 
     two of R 505  to R 508  may optionally be linked together to form a saturated or unsaturated ring. 
     In one or more embodiments, the fluorescent dopant may be a delayed fluorescence dopant that emits delayed fluorescence based on a delayed fluorescence emission mechanism. 
     For example, the delayed fluorescence dopant may be (i) a compound having a D-A structure (wherein D indicates an electron donor group, and A indicates an electron acceptor group) or (ii) a condensed cyclic compound containing boron (B). 
     In one or more embodiments, the delayed fluorescence dopant may include a compound represented by Formula 503-1 or 503-2: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 503-1 and 503-2, 
     Y 51  to Y 54  may each independently be a single bond, O, S, N[(L 506 ) xd6 -R 506 ], C[(L 506 ) xd6 -R 506 ][(L 507 ) xd7 -R 507 ], or Si[(L 506 ) xd6 -R 506 ][(L 507 ) xd7 -R 507 ], 
     m31 may be 0 or 1, 
     L 501  to L 507  are each as described in connection with L 501  in Formula 501, 
     xd1 to xd7 are each as described in connection with xd1 in Formula 501, 
     R 501  to R 507  may each independently be: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, or a C 1 -C 2 o alkylthio group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazole group, a triazinyl group, a dibenzofuranyl group, or a dibenzothiophenyl group; or 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, or a dibenzothiophenyl group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , a hydroxyl group, a cyano group, a nitro group, an amino group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 1 -C 20  alkylthio group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, or a combination thereof, 
     xd21 and xd23 may each independently be 0, 1, 2, 3, or 4, 
     xd22 and xd24 may each independently be 0, 1, 2, or 3, 
     xd25 may be 0, 1, or 2, and 
     two of R 501  to R 507  may optionally be linked together to form a saturated ring or an unsaturated ring. 
     The fluorescent dopant may include, for example, Compounds FD(1) to FD(16), or Compounds FD1 to FD14, or a combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the emission layer may be in a range of about 100 Å to about 1,000 Å, for example, about 200 Å to about 600 Å. When the thickness of the emission layer is within these ranges, excellent light-emission characteristics may be obtained without a substantial increase in driving voltage. 
     Next, the electron transport region may be located on the emission layer. 
     The electron transport region may include a hole blocking layer, an electron transport layer, an electron injection layer, or a combination thereof. 
     For example, the electron transport region may have a hole blocking layer/an electron transport layer/an electron injection layer structure or an electron transport layer/an electron injection layer structure, but embodiments are not limited thereto. The electron transport layer may have a single-layered structure or a multi-layered structure including two or more different materials. 
     Conditions for forming the hole blocking layer, the electron transport layer, and the electron injection layer which constitute the electron transport region may be similar to or the same as the conditions for forming the hole injection layer. 
     When the electron transport region includes a hole blocking layer, the hole blocking layer may include, for example, at least one of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), or bis(2-methyl-8-quinolinolato-N1,O8)-(1,1′-biphenyl-4-olato)aluminum (BAlq), but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
     
     A thickness of the hole blocking layer may be in a range of about 20 Å to about 1,000 Å, for example, about 30 Å to about 300 Å. When the thickness of the hole blocking layer is within these ranges, excellent hole blocking characteristics may be obtained without a substantial increase in driving voltage. 
     The electron transport layer may further include at least one of BCP, Bphen, tris(8-hydroxy-quinolinato)aluminum (Alq 3 ), BAlq, 3-(4-biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ), or 4-(naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole (NTAZ): 
     
       
         
         
             
             
         
       
     
     In one or more embodiments, the electron transport layer may include at least one of Compounds ET1 to ET25, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the electron transport layer may be in a range of about 100 Å to about 1,000 Å, for example, about 150 Å to about 500 Å. When the thickness of the electron transport layer is within these ranges, excellent electron transport characteristics may be obtained without a substantial increase in driving voltage. 
     The electron transport layer may include, in addition to the materials described above, a metal-containing material. 
     The metal-containing material may include a Li complex. The Li complex may include, for example, Compound ET-D1 (lithium quinolate, LiQ) or ET-D2: 
     
       
         
         
             
             
         
       
     
     The electron transport region may include an electron injection layer that facilitates electron injection from the second electrode  19 . 
     The electron injection layer may include at least one of LiF, NaCl, CsF, Li 2 O, or BaO. 
     A thickness of the electron injection layer may be in a range of about 1 Å to about 100 Å, for example, about 3 Å to about 90 Å. When the thickness of the electron injection layer is within these ranges, satisfactory electron injection characteristics may be obtained without a substantial increase in driving voltage. 
     The second electrode  19  may be located on the organic layer  15 . The second electrode  19  may be a cathode. A material for forming the second electrode  19  may be metal, an alloy, an electrically conductive compound, or a combination thereof, which has a relatively low work function. Examples of the material for forming the second electrode  19  may include one or more of lithium (Li), magnesium (Mg), aluminum (Al), silver (Ag), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), or magnesium-silver (Mg—Ag). In one or more embodiments, to manufacture a top-emission type light-emitting device, a transmissive electrode formed using ITO or IZO may be used as the second electrode  19 . 
     Hereinbefore, the organic light-emitting device has been described with reference to the FIGURE, but the exemplary embodiments are not limited thereto. 
     Another aspect provides a diagnostic composition including at least one organometallic compound represented by Formula 1. 
     The organometallic compound represented by Formula 1 provides high luminescence efficiency. Accordingly, a diagnostic composition including the organometallic compound may have high diagnostic efficiency. 
     The diagnostic composition may be applied in various ways, such as in a diagnostic kit, a diagnostic reagent, a biosensor, or a biomarker. 
     The term “C 1 -C 60  alkyl group” as used herein refers to a linear or branched saturated aliphatic hydrocarbon monovalent group having 1 to 60 carbon atoms. Examples thereof include a methyl group, an ethyl group, a propyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an iso-amyl group, and a hexyl group. The term “C 1 -C 60  alkylene group” as used herein refers to a divalent group having the same structure as the C 1 -C 60  alkyl group. 
     The term “C 1 -C 60  alkoxy group” as used herein refers to a monovalent group represented by -OA 101  (wherein A 101  is a C 1 -C 60  alkyl group). Examples thereof include a methoxy group, an ethoxy group, and an isopropyloxy group. 
     The term “C 1 -C 60  alkylthio group” used herein refers to a monovalent group represented by -SA 101′  (wherein A 101′  is the C 1 -C 60  alkyl group). 
     The term “C 2 -C 60  alkenyl group” as used herein refers to a group formed by including at least one carbon-carbon double bond in the middle or at the terminus of the C 2 -C 60  alkyl group. Examples thereof include an ethenyl group, a propenyl group, and a butenyl group. The term “C 2 -C 60  alkenylene group” as used herein refers to a divalent group having the same structure as the C 2 -C 60  alkenyl group. 
     The term “C 2 -C 60  alkynyl group” as used herein refers to a group formed by including at least one carbon-carbon triple bond in the middle or at the terminus of the C 2 -C 60  alkyl group. Examples thereof include an ethenyl group and a propenyl group. The term “C 2 -C 60  alkynylene group” as used herein refers to a divalent group having the same structure as the C 2 -C 60  alkynyl group. 
     The term “C 3 -C 10  cycloalkyl group” as used herein refers to a monovalent monocyclic saturated hydrocarbon group including 3 to 10 carbon atoms. Examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group. The term “C 3 -C 10  cycloalkylene group” as used herein refers to a divalent group having the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 1 -C 10  heterocycloalkyl group” as used herein refers to a monovalent monocyclic group including at least one heteroatom selected from N, O, P, Ge, Se, Si, and S as a ring-forming atom and 1 to 10 carbon atoms. Examples thereof include a tetrahydrofuranyl group and a tetrahydrothiophenyl group. The term “C 1 -C 10  heterocycloalkylene group” as used herein refers to a divalent group having the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term “C 3 -C 10  cycloalkenyl group” as used herein refers to a monovalent monocyclic group including 3 to 10 carbon atoms and at least one carbon-carbon double bond in its ring, wherein the molecular structure as a whole is non-aromatic. Examples thereof include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group” as used herein refers to a divalent group having the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group” as used herein refers to a monovalent monocyclic group including at least one heteroatom selected from N, O, P, Ge, Se, Si, and S as a ring-forming atom, 1 to 10 carbon atoms, and at least one double bond in its ring. Examples of the C 1 -C 10  heterocycloalkenyl group include a 2,3-dihydrofuranyl group and a 2,3-dihydrothiophenyl group. The term “C 1 -C 10  heterocycloalkenylene group” as used herein refers to a divalent group having the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group” as used herein refers to a monovalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms. The term “C 6 -C 60  arylene group” as used herein refers to a divalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms. Examples of the C 6 -C 60  aryl group include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a pyrenyl group, and a chrysenyl group. When the C 6 -C 60  aryl group and the C 6 -C 60  arylene group each include two or more rings, the two or more rings may be fused to each other. 
     The term “C 7 -C 60  alkyl aryl group” as used herein refers to a C 6 -C 60  aryl group substituted with at least one C 1 -C 60  alkyl group. The term “C 7 -C 60  aryl alkyl group” as used herein refers to a C 1 -C 60  alkyl group substituted with at least one C 6 -C 60  aryl group. 
     The term “C 1 -C 60  heteroaryl group” as used herein refers to a monovalent group having a heterocyclic aromatic system having at least one heteroatom selected from N, O, P, Ge, Se, Si, and S as a ring-forming atom and 1 to 60 carbon atoms. The term “C 1 -C 60  heteroarylene group” as used herein refers to a divalent group having a heterocyclic aromatic system having at least one heteroatom selected from N, O, P, Ge, Se, Si, and S as a ring-forming atom and 1 to 60 carbon atoms. Examples of the C 1 -C 60  heteroaryl group include a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group. When the C 6 -C 60  heteroaryl group and the C 6 -C 60  heteroarylene group each include two or more rings, the two or more rings may be fused to each other. 
     The term “C 2 -C 60  alkylheteroaryl group” as used herein refers to a C 1 -C 60  heteroaryl group substituted with at least one C 1 -C 60  alkyl group. The term “C 2 -C 60  heteroaryl alkyl group” as used herein refers to a C 1 -C 60  alkyl group substituted with at least one C 1 -C 60  heteroaryl group. 
     The term “C 6 -C 60  aryloxy group” as used herein refers to -0A 102  (wherein Aio2 is the C 6 -C 60  aryl group), and the term “C 6 -C 60  arylthio group” as used herein refers to SA 103  (wherein A 103  is the C 6 -C 60  aryl group). 
     The term “C 1 -C 60  heteroaryloxy group” as used herein indicates -0A 104  (wherein A 104  is a C 1 -C 60  heteroaryl group), and the term “C 1 -C 60  heteroarylthio group” as used herein indicates -SA 105  (wherein A 105  is the C 1 -C 60  heteroaryl group). 
     The term “monovalent non-aromatic condensed polycyclic group” as used herein refers to a monovalent group (for example, having 8 to 60 carbon atoms) having two or more rings condensed to each other, only carbon atoms as ring-forming atoms, and no aromaticity in its entire molecular structure. Examples of the monovalent non-aromatic condensed polycyclic group include a fluorenyl group. The term “divalent non-aromatic condensed polycyclic group” as used herein refers to a divalent group having the same structure as the monovalent non-aromatic condensed polycyclic group. 
     The term “monovalent non-aromatic condensed heteropolycyclic group” as used herein refers to a monovalent group (for example, having 2 to 60 carbon atoms) having two or more rings condensed with each other, at least one heteroatom selected from N, O, P, Ge, Se, Si, and S, other than carbon atoms, as a ring-forming atom, and no aromaticity in its entire molecular structure. Examples of the monovalent non-aromatic condensed heteropolycyclic group include a carbazolyl group. The term “divalent non-aromatic condensed heteropolycyclic group” as used herein refers to a divalent group having the same structure as the monovalent non-aromatic condensed heteropolycyclic group. 
     The term “C 5 -C 30  carbocyclic group” as used herein refers to a saturated or unsaturated cyclic group including 5 to 30 carbon atoms only as ring-forming atoms. The C 5 -C 30  carbocyclic group may be a monocyclic group or a polycyclic group. 
     The term “C 1 -C 30  heterocyclic group” as used herein refers to saturated or unsaturated cyclic group including 1 to 30 carbon atoms and at least one heteroatom selected from N, O P, Ge, Se, Si, and S as ring-forming atoms. The C 1 -C 30  heterocyclic group may be a monocyclic group or a polycyclic group. 
     At least one substituent of the substituted C 5 -C 30  carbocyclic group, the substituted C 1 -C 30  heterocyclic group, the substituted C 1 -C 60  alkyl group, the substituted C 2 -C 60  alkenyl group, the substituted C 2 -C 60  alkynyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 1 -C 60  alkylthio group, the substituted C 7 -C 60  aryl alkyl group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 1 -C 10  heterocycloalkyl group, the substituted C 3 -C 10  cycloalkenyl group, the substituted C 1 -C 10  heterocycloalkenyl group, the substituted C 6 -C 60  aryl group, the substituted C 7 -C 60  alkyl aryl group, the substituted C 6 -C 60  aryloxy group, the substituted C 6 -C 60  arylthio group, the substituted C 1 -C 60  heteroaryl group, the substituted C 2 -C 60  alkyl heteroaryl group, the substituted C 2 -C 60  heteroaryl alkyl group, the substituted C 1 -C 60  heteroaryloxy group, the substituted C 1 -C 60  heteroarylthio group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may be: 
     deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, or a C 1 -C 60  alkylthio group; 
     a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, or a C 1 -C 60  alkylthio group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a Ce-C 60  aryl group, a C 7 -C 60  alkyl aryl group, a Ce-C 60  aryloxy group, a Ce-C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q 11 )(Q 12 ), —Si(C 213 )(Q 14 )(Q 15 ), —B(Q 16 )(Q 17 ), —P(Q 18 )(Q 19 ), —P(═O)(Q 18 )(Q 19 ), or a combination thereof; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 6 -C 60  aryloxy group, a Ce-C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a Ce-C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one of deuterium, —F, —Cl, —Br, —I, —Sb 5 , —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 1 -C 60  alkylthio group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 7 -C 60  alkyl aryl group, a C 7 -C 60  aryl alkyl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 2 -C 60  heteroaryl alkyl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q 21 )(Q 22 ), —Si(Q 23 )(Q 24 )(Q 25 ), —B(Q 26 )(Q 27 ), —P(═O)(Q 28 )(Q 29 ), or a combination thereof; or 
     —N(Q 31 )(Q 32 ), —Si(Q 33 )(Q 34 )(Q 35 ), —B(Q 36 )(Q 37 ), —P(Q 38 )(Q 39 ), or —P(═O)(Q 38 )(Q 39 ), and 
     Q 1  to Q 9 , Q 11  to Q 19 , Q 21  to Q 29 , and Q 31  to Q 39  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, —SF 5 , a hydroxyl group, a cyano group, a nitro group, an am idino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 1 -C 60  alkylthio group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 7 -C 60  alkyl aryl group, a substituted or unsubstituted C 7 -C 60  aryl alkyl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, or a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group. 
     Hereinafter, a compound and an organic light-emitting device according to one or more exemplary embodiments will be described in further detail with reference to Synthesis Examples and Examples. However, the exemplary embodiments are not limited thereto. The wording “‘B’ was used instead of ‘A’” as used in describing Synthesis Examples means that an amount of ‘A’ used was identical to an amount of ‘B’ used, in terms of a molar equivalent. 
     EXAMPLES 
     Synthesis Example 1 
     Synthesis of Compound 1 
     (1) Synthesis of Intermediate 1(1) 
     
       
         
         
             
             
         
       
     
     10 grams (g) (36.6 millimoles (mmol)) of 1-(3-bromophenyl)-1H-benzo[d]imidazole and 18.7 g (47.6 mmol) of 9-(4-(tert-butyl)pyridin-2-yl)-6-phenyl-9H-carbazol-2-ol were dissolved in 360 milliliters (mL) of dimethyl sulfoxide (DMSO). Then, 2.1 g (11.0 mmol) of CuI, 31.1 g (146.4 mmol) of potassium phosphate (K3PO4), and 6.8 g (54.9 mmol) of picolinic acid were added thereto, followed by heating at reflux at a temperature of 100° C. for 12 hours. After completion of the reaction, the resultant was allowed to cool to room temperature, and an organic layer was extracted therefrom using a mixture of ethyl acetate and deionized (DI) water, the extracted organic layer was washed three times with DI water, the organic layer was then isolate dried using magnesium sulfate. Then, a solvent was removed therefrom under a reduced pressure to obtain a crude product. The crude product was purified by silica gel column flash chromatography (eluent: ethyl acetate and hexane) to obtain Intermediate 1(1) in a yield of 73%. 
     High performance liquid chromatograph-mass spectrometry (HPLC-MS): 585.24 [M+H] + . 
     (2) Synthesis of Intermediate 1(2) 
     
       
         
         
             
             
         
       
     
     7.0 g (12.0 mmol) of Intermediate 1(1), 16.4 g (30.0 mmol) of (bis(4-(t-butyl)-2,6-bis(methyl-d3)phenyl)iodonium tetrafluoroborane, and 1.1 g (6.0 mmol) of copper acetate (Cu(OAc) 2 ) were added to 50 mL of DMF, followed by heating at reflux at a temperature of 130° C. for 12 hours. The reaction was allowed to cool to room temperature and then a crude product was obtained by removing a solvent therefrom under a reduced pressure. The crude product was purified by silica gel flash column chromatography (eluent: dichloromethane and acetone) to obtain Intermediate 1(2) in a yield of 14%. 
     HPLC-MS: 751.41 [M-BE 4 ] + . 
     (3) Synthesis of Compound 1 
     
       
         
         
             
             
         
       
     
     0.6 g (1.7 mmol) of dichloro(1,5-cyclooctadiene)platinum(II) (Pt(COD)Cl 2 ), 1.4 g (1.7 mmol) of Intermediate 1(2), and 0.4 g (5.0 mmol) of sodium acetate (NaOAc) were added to 30 mL of benzonitrile, followed by heating at reflux at a temperature of 180° C. for 12 hours. After completion of the reaction, the resultant was allowed to cool to room temperature, and a solvent was removed therefrom under a reduced pressure to obtain a crude product. The crude product was purified by silica gel flash column chromatography (eluent: dichloromethane and hexane) to obtain Compound 1 in a yield of 30%. 
     HPLC-MS: 944.35 [M+H] + . 
     Synthesis Example 2: Synthesis of Compound 2 
     (1) Synthesis of Intermediate 2(1) 
     
       
         
         
             
             
         
       
     
     4.0 g (6.8 mmol) of Intermediate 1(1), 6.8 g (10.3 mmol) of (4,4′-di-t-butyl- [1,1′-biphenyl]-2-yl)(mesitypiodonium trifluoromethane sulfonate, and 0.13 g (0.7 mmol) of copper acetate (Cu(OAc)2) were added to 35 mL of DMF, followed by heating at reflux at a temperature of 130° C. for 12 hours. A crude product was obtained by removing a solvent therefrom under a reduced pressure. The crude product was purified by silica gel flash column chromatography (eluent: dichloromethane and acetone) to obtain Intermediate 2(1) in a yield of 51%. 
     HPLC-MS: 849.43 [M-OTf] + . 
     (2) Synthesis of Compound 2 
     
       
         
         
             
             
         
       
     
     3.5 g (3.5 mmol) of Pt(COD)Cl 2 , 1.3 g (3.5 mmol) of Intermediate 2(1), and 0.9 g 5.0 mmol) of NaOAc were added to 60 mL of benzonitrile, followed by heating at reflux at a temperature of 180° C. for 12 hours. After completion of the reaction, the resultant was allowed to cool to room temperature, and a solvent was removed therefrom under a reduced pressure to obtain a crude product. The crude product was subjected to silica gel column chromatography (eluent: dichloromethane and hexane) to obtain Compound 2 in a yield of 38%. 
     HPLC-MS: 1042.37 [M+H] + . 
     Synthesis Example 3 
     Synthesis of Compound 3 
     (1) Synthesis of Intermediate 3(1) 
     
       
         
         
             
             
         
       
     
     5.0 g (9.2 mmol) of 2-(3-(1H-benzo[d]imidazole-1-yl)phenoxy)-9-(4-(t-butyl)pyridine-2-yl)-6-chloro-9H-carbazole and 1.8 g (11.0 mmol) of 9H-carbazole were dissolved in 45 mL of xylene. Then, 0.5 g (0.9 mmol) of bis(dibenzylideneacetone)palladium(0) (Pd(dba)2), 1.8 g (18.4 mmol) of sodium tert-butoxide (NaOtBu), and 0.4 g (1.0 mmol) of 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (SPhos) were added thereto, followed by heating at reflux at a temperature of 110° C. for 12 hours. After completion of the reaction, the resultant was allowed to cool to room temperature, and an organic layer was extracted therefrom using a mixture of ethyl acetate and water. The organic layer was washed three times with DI water, isolated, and then dried using magnesium sulfate. Then, a solvent was removed therefrom under a reduced pressure to obtain a crude product. The crude product was purified by silica gel flash column chromatography (eluent: ethyl acetate and hexane) to obtain Intermediate 3(1) in a yield of 60%. 
     HPLC-MS: 674.28 [M+H] + . 
     (2) Synthesis of Intermediate 3(2) 
     
       
         
         
             
             
         
       
     
     Intermediate 3(2) (yield of 30%) was synthesized in a similar manner as was used to synthesize Intermediate 1(2) in Synthesis Example 1, except that Intermediate 3(1) was used instead of Intermediate 1(1), and bis(5-(t-butyl)-2-(methyl-d3)phenyl)iodonium tetrafluoro-borane was used instead of bis(4-(t-butyl)-2,6-bis(methyl-d3)phenyl)iodonium tetrafluoro-borane. 
     HPLC-MS: 823.34 [M-BE 4 ] + . 
     (3) Synthesis of Compound 3 
     
       
         
         
             
             
         
       
     
     Compound 3 (yield of 26%) was synthesized in a similar manner as was used to synthesize Compound 1 in Synthesis Example 1, except that Intermediate 3(2) was used instead of Intermediate 1(2). 
     HPLC-MS: 1015.42 [M+H] + . 
     Example 1 
     An ITO glass substrate was cut to a size of 50 millimeters (mm)×50 mm×0.5 mm, sonicated in acetone, isopropyl alcohol, and DI water, each for 15 minutes, and then exposed to UV irradiation and ozone for 30 minutes. 
     Then, a layer of m-MTDATA was deposited on an ITO electrode (anode) on the glass substrate at a deposition rate of 1 Å/sec to form a hole injection layer having a thickness of 600 Å, and then, a layer of α-NPD was deposited on the hole injection layer at a deposition speed of 1 Å/sec to form a hole transport layer having a thickness of 250 Å. 
     A layer of 10 wt % of Compound 1 (dopant) and CBP (host) were co-deposited on the hole transport layer at a deposition rate of 0.1 Å/sec and a deposition rate of 1 Å/sec, respectively, to form an emission layer having a thickness of 400 Å. 
     A layer of BAlq was deposited on the emission layer at a deposition rate of 1 Å/sec to form a hole blocking layer having a thickness of 50 Å, a layer of Alq 3  was deposited on the hole blocking layer to form an electron transport layer having a thickness of 300 Å, a layer of LiF was deposited on the electron transport layer to form an electron injection layer having a thickness of 10 Å, and then, a layer of Al was vacuum deposited on the electron injection layer to form a second electrode (cathode) having a thickness of 1,200 Å, thereby completing the manufacture of an organic light-emitting device having a structure of ITO/m-MTDATA (600 Å)/α-NPD (250 Å)/CBP+Compound 1 (10 wt %) (400 Å)/BAlq (50 Å)/Alq 3  (300 Å)/LiF (10 Å)/Al (1,200 Å). 
     
       
         
         
             
             
         
       
     
     Examples 2 and 3 and Comparative Examples 1 and 2 
     Organic light-emitting devices were manufactured in a similar manner as in Example 1, except that Compounds shown in Table 2 were each used instead of Compound 1 as a dopant in forming an emission layer. 
     Evaluation Example 1 
     Evaluation of Characteristics of Organic Light-emitting Devices 
     For each of the organic light-emitting devices manufactured according to Examples 1 to 3 and Comparative Examples 1 and 2, the maximum emission wavelength (λ max , nm), luminescence quantum efficiency (PLQY), and external quantum efficiency (EQE, %) were evaluated. The results are shown in Table 2. As evaluation apparatuses, a current-voltage meter (Keithley 2400) and a luminance meter (Minolta CS-1000A) were used. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Dopant in emission 
                 λ max   
                   
                 EQE 
               
               
                   
                   
                 layer 
                 (nm) 
                 PLQY 
                 (%) 
               
               
                   
                   
               
             
            
               
                   
                 Example 1 
                 Compound 1 
                 461 
                 0.622 
                 15.6 
               
               
                   
                 Example 2 
                 Compound 2 
                 462 
                 0.671 
                 16.6 
               
               
                   
                 Example 3 
                 Compound 3 
                 461 
                 0.671 
                 16.7 
               
               
                   
                 Comparative 
                 Compound A 
                 462 
                 0.653 
                 14.8 
               
               
                   
                 Example 1 
                   
                   
                   
                   
               
               
                   
                 Comparative 
                 Compound B 
                 462 
                 0.609 
                 14.5 
               
               
                   
                 Example 2 
               
               
                   
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                 
               
            
           
         
       
     
     From Table 2, it was confirmed that the organic light-emitting devices of Examples 1 to 3 had excellent luminescence quantum efficiency and external quantum efficiency, and were suitable for deep blue light emission. In particular, the organic light-emitting devices of Examples 1 to 3 had significantly greater external quantum efficiency compared to the organic light-emitting devices of Comparative Examples 1 and 2. 
     Example 4 
     An organic light-emitting device was manufactured in a similar manner as in Example 1, except that, in forming an emission layer, Compound CBP was used as a host at a weight ratio of 88.5 wt %, and Compound 3 and Compound FD14 were used as dopants at weight ratios of 10 wt % and1.5 wt %, respectively, each based on the total weight of the emission layer. 
     Comparative Example 3 
     An organic light-emitting device was manufactured in a similar manner as in Example 1, except that Compound FD14 was used as a dopant in forming an emission layer. 
     Evaluation Example 2 
     Evaluation of Characteristics of Organic Light-emitting Devices 
     For each of the organic light-emitting devices manufactured according to Example 4 and Comparative Example 3, the maximum emission wavelength (λ max , nm), external quantum efficiency (EQE, %, relative value), and lifespan characteristics (T 95 , %, relative value) were evaluated. The results are shown in Table 3. As evaluation apparatuses, a current-voltage meter (Keithley 2400) and a luminance meter (Minolta Cs-1000A) were used. The EQE are expressed as relative values based on Comparative Example 5 as 100%. The lifespan characteristics (T95) were evaluated by measuring the amount of time that elapsed until luminance was reduced to 95% of the initial luminance of 100% (the initial luminance was 1,000 candela per square meter (cd/m 2 ), or nits), and the results are expressed as relative values based on Comparative Example 5 as 100%. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                   
                 Lifespan 
               
               
                   
                   
                   
                 EQE 
                 (T 95 ) 
               
               
                   
                 Dopant  
                 λ max    
                 (relative 
                 (relative 
               
               
                 No. 
                 compound 
                 (nm) 
                 values) 
                 values) 
               
               
                   
               
             
            
               
                 Example 4 
                 Compound 3 + 
                 462 
                 182% 
                 741% 
               
               
                   
                 Compound FD14 
                   
                   
                   
               
               
                 Comparative 
                 Compound FD14 
                 462 
                 100% 
                 100% 
               
               
                 Example 5 
               
               
                   
               
            
           
         
       
     
     From Table 3, it was confirmed that the organic light-emitting device of Example 4 had significantly improved external quantum efficiency and lifespan characteristics compared to the organic light-emitting device of Comparative Example 3. 
     The organometallic compound has excellent photochemically stability, and an organic light-emitting device using the organometallic compound may have improved efficiency and lifespan. Accordingly, by using the organometallic compound, a high-quality organic light-emitting device may be realized. 
     It should be understood that the exemplary embodiments described herein should be considered in a descriptive sense and not for purposes of limitation. Descriptions of exemplary features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other exemplary embodiments. While one or more exemplary embodiments have been described with reference to the figure, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.