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

• A new azulene aza[4]helicene has been synthesized.
• A non-doped OLED based on the dye performed well.
• Potential use for circularly polarized (CP) light-emitting devices.

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 °C, respectively). The racemization barrier of the dyes is rather low, ∼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.

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