Synthesis and characterization of multi-substituted carbazole derivatives exhibiting aggregation-induced emission for OLED applications

A series of carbazole based derivatives differing in the number of dicyanovinyl acceptors and donors (N-alkyl carbazole or N-phenyl carbazole) are designed, synthesized and characterized. The effect of donors on optical, electrochemical and thermal properties of carbazole-dicyanovinyl dyads is critically analysed. The dyes containing C3-linked carbazole donor showed red-shifted absorption and larger molar extinction coefficients when compared to the dyes those containing N-phenylcarbazole attributable to the extended conjugation of C3-linked N-butylcarbazole. All the compounds showed positive solvatochromism in fluorescence attributable to intramolecular charge transfer in excited state. The higher thermal stability of the dyes suggests the rigidity of the carbazole derivatives. Interestingly, all the dyes containing N-phenylcarbazole showed aggregation-induced emission properties in THE-H2O mixtures attributable to increased distortion in molecular configuration and restricted rotation in the solid state. Furthermore, a green OLED device fabricated with the dye containing N-butyl carbazole donor as dopant emitter (3%) in CBP host achieved good performance with high external quantum efficiency (4.2%), current efficiency (13.1 cd A(-1)) and maximum brightness (L-max) of 6180 cd m(-2).