A compound of formula (I) wherein A 1 , A 2 and A 3 are represented by formula (II), (III), (IV), respectively whereby Ar 1 , Ar 2 and Ar 3 are independently selected from substituted or unsubstituted aryl, substituted or unsubstituted C 6 to C 24 aryl, substituted or unsubstituted heteroaryl or C 2 to C 24 heteroaryl, wherein the substituents on Ar 1 , Ar 2 and Ar 3 are independently selected form an electron-withdrawing group, NO 2 , CN, halogen, Cl, F, partially fluorinated or perfluorinated alkyl, partially fluorinated or perfluorinated C 1 to C 12 alkyl, CF3, partially fluorinated or perfluorinated alkoxy, partially fluorinated or perfluorinated C 1 to C 6 alkoxy or D; R', R" and R′′′ are independently selected from substituted or unsubstituted aryl, substituted or unsubstituted C 6 to C 18 aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted C 2 to C 18 heteroaryl, electron-withdrawing group, partially fluorinated or perfluorinated alkyl, partially fluorinated or perfluorinated C 1 to C 6 alkyl, halogen, F, CN, and NO 2 ; wherein in formulae (II) to (IV) each Ar 1 , Ar 2 and Ar 3 with the corresponding R', R'' and R′′′ can form a substituted or unsubstituted carbocyle or, preferably a substituted or unsubstituted heterocycle, wherein the substituents can be electron-withdrawing group, F, CN, perfluorinated C 1 to C 8 alkyl, substituted or unsubstituted C 6 to C 18 aryl, substituted or unsubstituted C 2 to C 18 heteroaryl, substituted or unsubstituted carbocyclene, substituted or unsubstituted carbocyclidene, substituted or unsubstituted alkylene, substituted or unsubstituted alkylidene; wherein the compound of formula (I) does not exhibit a glass transition temperature when measured by DSC during heating at 10 K/min. wherein A 1 , A 2 and A 3 are represented by formula (II), (III), (IV), respectively whereby Ar 1 , Ar 2 and Ar 3 are independently selected from substituted or unsubstituted aryl, substituted or unsubstituted C 6 to C 24 aryl, substituted or unsubstituted heteroaryl or C 2 to C 24 heteroaryl, wherein the substituents on Ar 1 , Ar 2 and Ar 3 are independently selected form an electron-withdrawing group, NO 2 , CN, halogen, Cl, F, partially fluorinated or perfluorinated alkyl, partially fluorinated or perfluorinated C 1 to C 12 alkyl, CF3, partially fluorinated or perfluorinated alkoxy, partially fluorinated or perfluorinated C 1 to C 6 alkoxy or D; R', R" and R′′′ are independently selected from substituted or unsubstituted aryl, substituted or unsubstituted C 6 to C 18 aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted C 2 to C 18 heteroaryl, electron-withdrawing group, partially fluorinated or perfluorinated alkyl, partially fluorinated or perfluorinated C 1 to C 6 alkyl, halogen, F, CN, and NO 2 ; wherein in formulae (II) to (IV) each Ar 1 , Ar 2 and Ar 3 with the corresponding R', R'' and R′′′ can form a substituted or unsubstituted carbocyle or, preferably a substituted or unsubstituted heterocycle, wherein the substituents can be electron-withdrawing group, F, CN, perfluorinated C 1 to C 8 alkyl, substituted or unsubstituted C 6 to C 18 aryl, substituted or unsubstituted C 2 to C 18 heteroaryl, substituted or unsubstituted carbocyclene, substituted or unsubstituted carbocyclidene, substituted or unsubstituted alkylene, substituted or unsubstituted alkylidene; wherein the compound of formula (I) does not exhibit a glass transition temperature when measured by DSC during heating at 10 K/min. <EOS>