A compound of formula 1: wherein X is O; R 1 is selected from a substituted or unsubstituted C 1 to C 18 alkyl group, wherein the substituents of the substituted C 1 to C 18 alkyl group are selected from C 6 to C 24 aryl, C 3 to C 24 heteroaryl, halogen, CN, perfluorinated C 1 to C 16 alkyl, perfluorinated C 1 to C 16 alkoxy; Ar 1 is selected from an unsubstituted C 6 to C 24 aryl; L is selected from a substituted or unsubstituted C 6 to C 19 arylene or C 3 to C 24 heteroarylene group, wherein the substituents of the substituted C 6 to C 19 arylene or of the substituted C 3 to C 24 heteroarylene group are independently selected from C 1 to C 16 alkyl, C 1 to C 16 alkoxy, C 6 to C 24 aryl, C 3 to C 24 heteroaryl, perfluorinated C 1 to C 16 alkyl, perfluorinated C 1 to C 16 alkoxy; Ar 2 is selected from a substituted or unsubstituted C 10 to C 42 aryl or substituted or unsubstituted C 3 to C 42 heteroaryl group, wherein the C 10 to C 42 aryl group comprises a conjugated system of delocalized electrons having at least 10 conjugated delocalized electrons, and wherein the substituents of the substituted C 10 to C 42 aryl group or of the substituted C 3 to C 42 heteroaryl group are independently selected from C 1 to C 16 alkyl, C 1 to C 16 alkoxy, substituted or unsubstituted C 6 to C 36 aryl, substituted or unsubstituted C 3 to C 36 heteroaryl, halogen, CN, perfluorinated C 1 to C 16 alkyl, perfluorinated C 1 to C 16 alkoxy, PXR 3 R 4, L-PXR 3 R 4, COR 5; wherein R 3, R 4 and R 5 are independently selected from C 1 to C 16 alkyl, C 6 to C 24 aryl, C 3 to C 24 heteroaryl, perfluorinated C 1 to C 16 alkyl, and wherein the substituent of the substituted C 6 to C 36 aryl or of the substituted C 3 to C 36 heteroaryl are independently selected from C 1 to C 16 alkyl, C 1 to C 16 alkoxy, C 6 to C 18 aryl, C 4 to C 18 heteroaryl, CN, halogen; n is an integer selected from 1, 2 or 3; and excluding compound 2, wherein R' is selected from C 1 to C 4 alkyl, and R" is selected from 1-naphthyl, (1,1'-biphenyl)-2-yl and/or 2-methoxy-1-naphthalene-yl; wherein formula 1 comprises at least 6 to 25 aromatic rings. X is O; R 1 is selected from a substituted or unsubstituted C 1 to C 18 alkyl group, wherein the substituents of the substituted C 1 to C 18 alkyl group are selected from C 6 to C 24 aryl, C 3 to C 24 heteroaryl, halogen, CN, perfluorinated C 1 to C 16 alkyl, perfluorinated C 1 to C 16 alkoxy; Ar 1 is selected from an unsubstituted C 6 to C 24 aryl; L is selected from a substituted or unsubstituted C 6 to C 19 arylene or C 3 to C 24 heteroarylene group, wherein the substituents of the substituted C 6 to C 19 arylene or of the substituted C 3 to C 24 heteroarylene group are independently selected from C 1 to C 16 alkyl, C 1 to C 16 alkoxy, C 6 to C 24 aryl, C 3 to C 24 heteroaryl, perfluorinated C 1 to C 16 alkyl, perfluorinated C 1 to C 16 alkoxy; Ar 2 is selected from a substituted or unsubstituted C 10 to C 42 aryl or substituted or unsubstituted C 3 to C 42 heteroaryl group, wherein the C 10 to C 42 aryl group comprises a conjugated system of delocalized electrons having at least 10 conjugated delocalized electrons, and wherein the substituents of the substituted C 10 to C 42 aryl group or of the substituted C 3 to C 42 heteroaryl group are independently selected from C 1 to C 16 alkyl, C 1 to C 16 alkoxy, substituted or unsubstituted C 6 to C 36 aryl, substituted or unsubstituted C 3 to C 36 heteroaryl, halogen, CN, perfluorinated C 1 to C 16 alkyl, perfluorinated C 1 to C 16 alkoxy, PXR 3 R 4, L-PXR 3 R 4, COR 5; wherein R 3, R 4 and R 5 are independently selected from C 1 to C 16 alkyl, C 6 to C 24 aryl, C 3 to C 24 heteroaryl, perfluorinated C 1 to C 16 alkyl, and wherein the substituent of the substituted C 6 to C 36 aryl or of the substituted C 3 to C 36 heteroaryl are independently selected from C 1 to C 16 alkyl, C 1 to C 16 alkoxy, C 6 to C 18 aryl, C 4 to C 18 heteroaryl, CN, halogen; wherein R 3, R 4 and R 5 are independently selected from C 1 to C 16 alkyl, C 6 to C 24 aryl, C 3 to C 24 heteroaryl, perfluorinated C 1 to C 16 alkyl, and wherein the substituent of the substituted C 6 to C 36 aryl or of the substituted C 3 to C 36 heteroaryl are independently selected from C 1 to C 16 alkyl, C 1 to C 16 alkoxy, C 6 to C 18 aryl, C 4 to C 18 heteroaryl, CN, halogen; n is an integer selected from 1, 2 or 3; and wherein R' is selected from C 1 to C 4 alkyl, and R" is selected from 1-naphthyl, (1,1'-biphenyl)-2-yl and/or 2-methoxy-1-naphthalene-yl; wherein formula 1 comprises at least 6 to 25 aromatic rings.