Preparation of 4,7-dihetaryl-1,2,5-oxadiazolo[3,4-c]pyridines as red fluorescent materials

A series of 1,2,5-oxadiazolo[3,4-c]pyridines (6, 7, 8 and 10) with thiophene, furan, and benzothiophene rings at the 4 and 7 positions were prepared, in quest of a red fluorescent material useful in OLED devices. Compound (6, 7, 8 and 10) emit fluorescence of orange to red color in solution and in the solid state. 6-Cyano derivatives (6) show a higher quantum yield than the corresponding esters (7), the phenyl derivative (8), and the unsubstituted compound (10). Red EL light at γ = 680 nm was obtained in an OLED device when 4,7-bis(5-phenylthien-2-yl) ester (7h) was used as a dopant emitter.