Abstract:
Fluorinated aromatic materials, their synthesis and their use in optoelectronics. In some cases, the fluorinated aromatic materials are perfluoroalkylated aromatic materials that may include perfluoropolyether substituents.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of U.S. application Ser. No. 13/391,375, filed on May 2, 2012, which is a National Stage Entry of PCT/US2010/046207, filed on Aug. 20, 2010, which claims the benefit of provisional patent application Ser. No. 61/235,970, entitled “FLUORINATED AROMATIC MATERIALS AND THEIR USE IN OPTOELECTRONICS,” filed on Aug. 21, 2009. The entire disclosures of which are hereby expressly incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The United States government may have certain rights to this invention. 
    
    
     TECHNICAL FIELD 
     The disclosure pertains generally to fluorinated aromatic materials, their synthesis and their use in optoelectronics. 
     BACKGROUND 
     Fluorinated aromatics and related materials offer many advantages over non-fluorinated materials in a variety of different optoelectronic devices such as, but not limited to, organic light emitting diodes, organic field-effect transistors, organic solar cells, and dye-sensitized solar cells. These fluorinated materials have processing advantages and are thermally and photochemically stable. They have reduced flammability tolerance to extreme environmental conditions, including superhydrophobicity and oleophobicity. Fluorinated materials also have advantages in tuning the electronic and optical properties of these devices. For example, these materials can be used to produce oxygen stable n-type semiconductors that can be used in organic solar cells, dye-sensitized solar cells, polymer solar cells, organic light emitting diodes (OLEDs), organic thin-film field-effect transistors (OFETs). 
     SUMMARY 
     The invention is directed to fluorinated aromatic materials, their synthesis and their use in optoelectronics. In some embodiments, the fluorinated aromatic materials are perfluoroalkylated aromatic materials that may include perfluoropolyether substituents. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an electronic image illustrating hydrophobicity. 
         FIG. 2  is an electronic image illustrating luminescence. 
         FIG. 3  is a graph illustrating the photostability of perfluoroalkylated anthracenes. 
         FIG. 4  is a graph illustrating the photostability of perfluoroalkylated pyrenes. 
         FIG. 5  is a schematic illustration of a heterojunction organic blue light emitting diode (OLED). 
         FIG. 6  is a schematic illustration of a homojunction organic blue light emitting diode (OLED). 
         FIG. 7  is a schematic illustration of a heterojunction flexible organic solar cell (OSC). 
     
    
    
     DETAILED DESCRIPTION 
     Fluorinated materials such as fluorinated aromatic materials have strongly enhanced luminescence, higher chemical stability and higher photostability when compared to corresponding non-fluorinated aromatic materials. Fluorinated aromatic materials are also highly hydrophobic and oleophobic, which may be useful in limiting proton-related reduction of the aromatic.  FIG. 1  illustrates the hydrophobic nature of fluorinated materials. In  FIG. 1 , a water drop is seen on a solid perfluoroalkylated dye covered glass slide.  FIG. 2  illustrates the luminescence. In  FIGS. 2A and 2B , the photoluminescence of, from left to right, anthracence, 9,10-dibromo anthracene and 9,10-bis(perfluorooctyl)anthracene is seen.  FIG. 2C  provides a graphical representation of luminescence intensity for anthracene and 9,10-bis(perfluorooctyl)anthracene. 
       FIGS. 3 and 4  illustrate the photostability of the fluorinated aromatic materials described herein. In  FIGS. 3 and 4 , the materials were tested with a 300 W Xe light with a 1.5 AM filter. The Y axis shows the percentage of the tested compounds remaining after being exposed to light for a particular amount of time.  FIG. 3  compares fluorinated and non-fluorinated anthracene derivatives while  FIG. 4  compares fluorinated and non-fluorinated pyrene derivatives. 
     In some embodiments, the fluorinated aromatic materials have fluorinated side chains that include sp 3  hydridized carbon atoms. In some embodiments, C sp3 —F functional groups are much more chemically resistant than C sp2 —F functional groups, which in some cases are susceptible to nucleophilic aromatic substitution when strong nucleophiles are present. Although the C sp2 —F bond is stable against oxidation, it can undergo reductive defluorination, especially when reducing metals and reagents are present or under electrochemical reducing conditions. 
     In some embodiments, the fluorinated aromatic materials are perfluoroalkylated aromatic materials that may include perfluoropolyether substituents. These materials may include at least one perfluoroalkyl group or semi-perfluoroalkyl group on the aromatic core structure. Illustrative but non-limiting examples of aromatic core structures include pyrroles, thiophenes, benzenes, naphthalenes, anthracenes, acenaphthene, acenaphthylene, fluorene, phenalene, phenanthrene, benzo[a]anthracene, benzo[a]fluorine, benzo[c]phenanthrene, chrysene, fluoranthene, pyrenes, tetracenes, triphenylene, anthanthrene, benzopyrene, benzo[a]pyrene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, benzo[ghi]perylene, corannulene, coronene, dicoronylene, diindenoperylene, helicene, heptacene, hexacene, kekulene, ovalene, pentacene, perylene, picene, tetraphenylenepentacenes, fullerenes, bi-pyridines, ter-pyridines, quinolines, phenanthrolines, porphyrins, benzoporphyrins, and phthalocyanines. 
     In some embodiments, fluorinated aromatic materials may be of the formula:
 
Ar—(R) x -(Q) y -(G) z,  
 
where Ar is an aromatic core including 3 to about 120 sp 2  hybridized carbon atoms or a total of 3 to about 120 sp 2  hybridized carbon atoms, nitrogen atoms, oxygen atoms and sulfur atoms; R is a perfluoroalkyl group of the formula C n F 2n+1 , n is an integer ranging from 1 to about 30; Q is a perfluoropolyether group of the formula C k F 2k+1 O h , k is an integer ranging from 1 to about 1000, h is an integer less than or equal to k−1; G is an organic functional group selected from the group consisting of hydrogen, C 1-30  alkyl, C 3-30  aryl, halogen, nitro, cyano, ester, ether, hydroxyl, aryl group bearing substituents including one or more of carbon, fluorine, chlorine, bromine, nitro or methoxy, or an aryl group including a heteroatom such as N, O and S; x, y and z are integers such that x+y+z is less than or equal to the total number of sp 2  hybridized carbon atoms, nitrogen atoms, oxygen atoms and sulfur atoms within the aromatic core, and y and z may independently be zero.
 
     In some embodiments, the aromatic core may be selected from the group consisting of benzene, naphthalene, anthracene, pyrene, coronene, phenanthroline, bi-pyridine and ter-pyridine. In some embodiments, R may be C 8 F 17  and x is in the range of 2 to 6. In some embodiments, G may be hydrogen, C 1-30  alkyl, C 3-30  aryl, halogen, nitro, cyano, ester, ether or hydroxyl. 
     In some embodiments, the perfluoroalkylated heterocyclic aromatics may form metal complexes with metals such as Li, Na, K, Mg, Ca, Al, P, S, Se, As, Ge, Ga, In, Sn, Sb, Tl, Pb, Bi, Sr, Ba, Sc, Y, Ti, V, Cr, Mn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Fe, Co, Ni, Cu, Au, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, and lanthanides with formal oxidation states from +1 to +6. In some embodiments, the heterocyclic aromatic cores may be selected from the group consisting of phenanthroline, bi-pyridine, ter-pyridine, and quinoline. In some embodiments, a metal complex may be one or more molecules selected from the group consisting of 
                                
in which n may be between about 1 and about 30.
 
     In some embodiments, a fluorinated aromatic material may be one or more molecules selected from the group consisting of: 
     
       
                 
         
             
             
         
      
       
                 
         
             
             
         
       
     
     In some embodiments, n is between about 1 and about 30. In other embodiments, n is between about 2 and about 30. 
     In some embodiments, a fluorinated aromatic material may be 9,10-bis-perfluorooctyl anthracene, which has the structure: 
     
       
                 
         
             
             
         
      
     
     In some embodiments, a fluorinated aromatic material may be 1,3,6,8-tetrakis perfluorooctyl pyrene, which has the structure: 
     
       
                 
         
             
             
         
      
     
     In some embodiments, a fluorinated aromatic material may be 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene, which has the structure: 
     
       
                 
         
             
             
         
      
     
     In some embodiments, a fluorinated aromatic compound may be 5,6-bisperfluorooctyl-1,10-phenanthroline, which has the structure: 
     
       
                 
         
             
             
         
      
     
     In some embodiments, perfluoroalkylated and semi-perfluoroalkylated aromatics and heterocyclic aromatics and related polymers may be synthesized via transition metal mediated/catalyzed cross-coupling reactions from corresponding halogenated aromatic precursors (Ar—X, where X is F, Cl, Br or I) and perfluoroalkyl halide (RfX, where X is Cl, Br or I). In some embodiments, the perfluoroalkylation reaction may be copper mediated and may be carried out under a nitrogen atmosphere. In some embodiments, the perfluoroalkyl group may be abbreviated as C n F 2n+1  in which n is an integer between 1 and 18 and the semi-perfluoroalkyl group may be abbreviated as C m H 2m C n F 2+1  in which m is an integer between 1 and 3 and n is an integer between 1 and 17. 
     In some embodiments, polar aprotic solvents, such as DMSO or DMF, with cupper mediator, work well for many aromatic halides (bromide and iodide). However, since DMSO and DMF are fluorophobic instead of fluorophilic, the reaction intermediates of perfluoroalkylated compounds are almost insoluble in these fluorophobic solvents. The insolubility of the reaction intermediates lead to an incomplete reaction and multiple side products, including isomers that are very difficult to separate. 
     In some embodiments, polar fluorophilic solvents (e.g. benzotrifluoride) may be used as co-solvents to dissolve the reaction intermediates. As a result, the perfluoroalkylation reaction goes to completion and gives almost exclusively the target product for most of the reactions under optimized conditions. Examples of suitable polar fluorophilic solvents include benzotrifluoride and the fluorinated ethers available commercially from 3M under the tradenames HFE-7100®, HFE-7200® and HFE-7500®. 
     In some embodiments, perfluoroalkylated aromatic materials may be made in accordance with the following reaction scheme: 
     
       
                 
         
             
             
         
      
     
     In some embodiments, perfluoroalkylated aromatic materials may be directly synthesized by perfluoroalkylating a brominated aromatic molecule. In some embodiments, perfluoroalkylated aromatic materials may be synthesized through a stepwise bromination, perfluoroalkylation, further bromination and so on. 
     The fluorinated aromatic materials described herein may be used in a variety of optoelectronic devices. Illustrative but non-limiting examples of suitable uses include organic solar cells, dye-sensitized solar cells, polymer solar cells, organic light emitting diodes (OLEDs), organic thin-film field-effect transistors (OFETs), laser diodes, two-photon absorption materials, multifunctional biomedical imaging reagents including reagents for MRI, ultrasounds, NIR fluorescence, photodynamic therapy and others. In some embodiments, these materials may be used to form air stable and moisture resistant n-type semiconductors. 
       FIG. 5  is a schematic illustration of a heterojunction organic blue light emitting diode (OLED)  10  that utilizes both fluorinated and non-fluorinated materials. The OLED  10  may be constructed via chemical vapor deposition, physical vapor deposition and a thickness-controlled spin coating method in which the thickness of each element and layer is controlled. The OLED  10  includes a conducting carbon fiber cathode  12  and a fluorinated n-type semiconductor  14 . Commercial carbon fiber may be used for the conducting carbon fiber cathode  12 . The fluorinated n-type semiconductor  14  may be formed of a perfluoroalkylated pyrene of the structure shown, in which n may be an integer ranging from about 0 to about 17. The OLED  10  includes a p-type non-fluorinated semiconductor  16  that may, in some embodiments, be formed of the same material as the n-type semiconductor  14  but without the perfluoroalkyl substituent groups. The OLED  10  may include a perfluoroalkylated conducting polymer anode  16  and a conducting glass or polymer substrate  18 . Printed silver wire is used as the electrical connectors  22 . The perfluoroalkylated conducting polymer anode  16  may be formed of poly 3,4-perfluoroalkyl pyrroles and/or poly 3,4-perfluoroalkyl thiophenes having the following structures: 
                                
in which n is in the range of about 1 to about 30 and mi is in the range of about 1 to about 10,000.
 
       FIG. 6  is a schematic illustration of a homojunction organic blue light emitting diode (OLED)  24  that includes fluorinated aromatic materials such as those discussed above. The OLED  24  may be constructed via chemical vapor deposition, physical vapor deposition and a thickness-controlled spin coating method in which the thickness of each element and layer is controlled. The OLED  24  includes a conducting carbon fiber cathode  26  formed of commercial conducting carbon fiber and a fluorinated n-type semiconductor  28 . The fluorinated n-type semiconductor  28  may be formed of a perfluoroalkylated anthracene of the structure shown. The OLED  24  may include a perfluoroalkylated conducting polymer anode  30  and a conducting glass or polymer substrate  32 . Printed silver wire is used as the electrical connectors  34 . The perfluoroalkylated conducting polymer anode  30  may be formed of the poly 3,4-perfluoroalkyl pyrroles and poly 3,4-perfluoroalkyl thiophenes described above with respect to  FIG. 5 . 
       FIG. 7  is a schematic illustration of a heterojunction flexible organic solar cell (OSC)  36  that is constructed using fluorinated aromatic materials (e.g. perfluoroalkylated porphyrins, perfluoroalkylated benzoporphyrins, and perfluoroalkylated phthalocyanines), fluorinated polymers, and nonfluorinated materials as p-type semiconductors (e.g. benzoporphyrins, phthalocyanines). The OSC  36  may be constructed via chemical vapor deposition, physical vapor deposition and a thickness-controlled spin coating method in which the thickness of each element and layer is controlled. The OSC  36  includes a perfluoroalkylated (e.g. poly 3,4-perfluoroalkyl thiophene) conducting polymer cathode  38  and a fluorinated n-type semiconductor  40  that may be formed of any of the fluorinated aromatic materials discussed herein. The OSC  36  includes a non-fluorinated p-type semiconductor  42  and a perfluoroalkylated conducting polymer anode  44 . The OSC  36  includes a conducting substrate  46 . Printed silver wire is used as the electrical connectors  48 . The perfluoroalkylated conducting polymer anode  44  may be formed of the poly 3,4-perfluoroalkyl pyrroles and poly 3,4-perfluoroalkyl thiophenes described above with respect to  FIG. 5 . 
     EXAMPLES 
     Example 1 
     Synthesis of 1,3,6,8-Tetrakis-perfluorooctyl-pyrene 
     Perfluorooctyl iodide (C 8 F 17 I, 1.10 ml, 4.13 mmol) was added into a mixture of 1,3,6,8-Tetrabromopyrene (0.146 g, 0.25 mmol) and copper powder (0.525 g, 8.26 mmol) in α,α,α-trifluorotoluene and anhydrous DMSO under nitrogen protection at 130-135° C. 1,3,6,8-Tetrabromopyrene was prepared from pyrene through direct bromonation. The reaction was monitored by TLC and quenched after 5 hours with acidic ice water. The mixture was suction filtered and the precipitate was washed at least three times with hydrochloric acid and D.I. water, then the solid crude product (ash gray) was further extracted with HFE-7200® to yield white crystalline 1,3,6,8-tetrakis-perfluorooctyl-pyrene (0.363 g, 75%) with bright blue fluorescence. Characterization data: 1H-NMR: 8.65 ppm (1H) and 8.82 ppm (2H). 
     Example 2 
     Synthesis of 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene 
     Perfluorooctyl iodide (C 8 F 17 I, 3.28 ml, 12.4 mmol) was added into a mixture of 2,6,9,10-tetrabromoanthracene (0.494 g, 1 mmol) and copper powder (1.576 g, 24.8 mmol) in α,α,α-trifluorotoluene and anhydrous DMSO under nitrogen protection at 130-135° C. 2,6,9,10-tetrabromoanthracene was prepared from anthracene through direct bromonation. The reaction was monitored by TLC and quenched after 4 hours with ice water. The mixture was worked up with standard extraction methylene chloride and toluene and filtration to give 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene in good yield. mp 94-96° C. 
     Characterization data: 1H NMR (CDCl 3 ): δ 9.00 ppm (s, 2H), 8.75 ppm (d, 2H), 7.85 ppm (d, 2H); 19F NMR (CDCl 3 ); δ −80.57 ppm (t, 23.34 Hz, 12F), −90.91 ppm (m, 8F), −111.62 ppm (m, 8F), −116.81 ppm (m, 8F), −121.46 ppm (m, 8F), −121.84 ppm (m, 8F), −122.86 ppm (m, 8F), −126.08 ppm (m, 8F); MS (LRFAB pos ion); m/z (m+) 1850.0 (calcd for C 46 H 6 F 68 : 1850.4): C, H analysis; Calcd (%) for C 46 H 6 F 68  is C, 29.85; H, 0.32. found C, 29.67; H, 0.19. 
     Example 3 
     Synthesis of 9,10-bis-perfluorooctyl-anthracene 
     Perfluorooctyl iodide (C 8 F 17 I, 2.36 ml, 8.93 mmol) was added into a mixture of 9,10-dibromoanthracene (0.6 g, 1.78 mmol) and copper powder (1.14 g, 17.8 mmol) in trifluorotoluene and anhydrous DMSO under nitrogen protection at 130° C. 9.10-dibromoanthrocene is commercially available. The reaction was monitored by TLC and quenched after 4 hours with ice water. The mixture was worked up with standard extraction with methylene chloride to give 9,10-bis-perfluorooctyl-anthracene in good yield. 
     Characterization data: mp 128-132° C.; 1H NMR (CDCl 3 ): δ 8.42 ppm (d, 4H), 7.61 ppm (d, 4H); 19F NMR (CDCl 3 ); δ −80.56 ppm (t, 21.36 Hz, 6F), −90.86 ppm (m, 4F), −116.68 ppm (m, 4F), −121.21 ppm (m, 4F), −121.57 ppm (m, 4F), −122.88 ppm (m, 4F), −125.88 ppm (m, 4F), −125.91 ppm (m, 8F); MS (LRFAB pos ion); m/z (m+) 1014.0 (calcd for C 30 H 8 F 34 : 1014.3): C, H analysis; Calcd (%) for C 30 H 8 F 34  is C, 35.52; H, 0.78. found C, 35.17; H, 0.74. 
     Example 4 
     Synthesis of 5,6-bisperfluorooctyl-1,10-phenanthroline 
     0.5 g (1.47 mmol) of 5,6-dibromo-1,10-phenanthroline, 1.13 g (17.78 mmol) of copper powder were added into a three neck round bottom flask with α,α,α-trifluorotoluene and DMSO. When the temperature inside the reaction mixture reached 106° C., 2.4 ml (8.9 mmol) of C 8 F 17 I was added drop wise over 45 min and the reaction was run for 3 hrs. The reaction mixture was allowed to cool to room temperature and 200 ml of chloroform was added. The mixture was then washed with 6×100 ml of concentrated ammonium hydroxide solution, followed by washing with 3×100 ml of D.I. water. The chloroform layer was then collected, dried, and removed to yield crude product, which was further recrystallized from methylene chloride. 
     Characterization data:  1 H NMR (CDCl 3 ): δ 9.22 ppm, 8.69 ppm, 7.92 ppm;  19 F NMR (CDCl 3 ); δ −80.62 ppm (t, 6F), −104.61 ppm (m, 4F), −119.79 ppm (m, 4F), −121.09 ppm (m, 4F), −121.58 ppm (m, 4F), −121.76 ppm (m, 4F), −122.58 ppm (m, 4F), −125.98 ppm (m, 4F); MS (LRFAB); m/z (m + ) 1016.8 (calcd for C 28 H 6 F 34 N 2 : 1016.3). 
     Example 5 
     Synthesis of 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene in HFE-7200 
     Perfluorooctyl iodide (C 8 F 17 I, 3.28 ml, 12.4 mmol) was added into a mixture of 2,6,9,10-tetrabromoanthracene (0.494 g, 1 mmol) and copper powder (1.576 g, 24.8 mmol) in HFE-7200® and anhydrous DMSO under nitrogen protection at 90° C. The reaction was monitored by TLC and cooled down to room temperature after 24 hours. The mixture was separated directly to give a HFE-7200® solution of 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene. Removal of the HFE-7200® solvent yielded the solid product 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene having characterization data matching that of Example 2. 
     Example 6 
     Thin Film Production of 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene with HFE-7200 
     5 mg of 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene was dissolved in 1.0 mL of HFE-7200 and spin coated onto a glass slide a room temperature and atmosphere pressure. The thin film was stable with treatment of water and hydrocarbon based non-halogen solvents, and stable under sunlight (tested with 1.5 AM solar simulator). 
     Prophetic Example 
     Synthesis of 2,4,6,8,9,10-hexa-heptadecafluorooctyl-anthracene 
     Step one: 2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene (1 mmol) is dissolved into 50 ml of HFE-7500® and heated up in a 130° C. oil bath Anhydrous AlBr 3  (0.05 mmol) and DBI solid (1.2 mmol) are added into the reaction mixture under string. After 24 hours at 130° C. the reaction mixture will be cooled down to room temperature, and washed with water. The HFE-7500® solution is evaporated to yield 4,8-dibromo-2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene. 
     Step two: Perfluorooctyl iodide (C 8 F 17 I, 2.5 mmol) is added into a mixture of 4,8-dibromo-2,6,9,10-tetrakis-heptadecafluorooctyl-anthracene (0.5 mmol) and copper powder (5.0 mmol) in HFE-7500 and anhydrous DMSO under nitrogen protection at 130° C. The reaction is monitored by TLC and cooled down to room temperature after 72 hours. The mixture will be separated directly to give a HFE-7500 solution of 2,4,6,8,9,10-hexa-heptadecafluorooctyl-anthracene. Removal of HFE-7500 will give solid compound 2,4,6,8,9,10-hexa-heptadecafluorooctyl-anthracene. 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the above described features.