| abstract |
In OLEDs, improved efficiency is obtained by compounds which can form inter alia electron injection layers of the formula (I) n n n n n n n n n n whereinn R 1 is a 1-5 ring aryl (including polycyclic), aralkyl or heteroaryl group which is optionally substituted with one or more C 1 -C 4 alkyl, alkoxy or cyano; R 2 and R 3 together form a 1-5 ring aryl (including polycyclic), aralkyl or heteroaryl group which is optionally substituted with C 1 -C 4 alkyl, alkoxy or cyano; R 4 is hydrogen, C 1 -C 4 alkyl or aryl; and Ar is monocyclic, bicyclic or tricyclic aryl or heteroaryl which is optionally substituted with one or more C 1 -C 4 -alkyl or alkoxy groups, or an oligomer thereof. |