Organic light emitting diodes (OLED) based on helical structures containing 7-membered fused rings

Three novel isomeric helical molecules 2-methoxy-m,n-dimethyl-6-phenyl-6H-5,6,7-triazadibenzo[f,h] naphtho[3,2,1-cd]azulenes (m,n = 8,9; 8,10; 9,10), derived from alkylated 1H-pyrazolo[3,4-b]quinoline halides, were synthesized. Their twisted structures containing a seven-membered ring help to sustain a glassy state, which enables a film of good quality to be formed. All compounds exhibit distinct glass transition temperatures (98, 100 and 113 degrees C, respectively). The racemization barrier of the dyes is rather low, similar to 25 kcal/mol. In consequence the compounds were obtained as racemic mixtures, both in solution and crystalline state. The helical structure of azulenes can be clearly seen from their crystal structures; however the racemates belong to centrosymmetric space groups. Finally, the helical dyes were successfully applied as a direct light emitting layer in OLED cell. The configuration of the devices: ITO/PEDOT:PSS/azulene/Ca/Al, emitting greenish-yellow light with CIE coordinates (0.44, 0.54) is reported. (C) 2014 Elsevier Ltd. All rights reserved.