Regulation of the light color and electroluninescence of rigid orthogonally linked hybrid local and charge-transfer (HLCT) material: Intramolecular charge-transfer and intermolecular excimer

Rational regulation on the hybrid local and charge-transfer (HLCT) excited state is crucial for the optimization of light color, especially those of the blue-emissive materials. In this work, two rigid, orthogonal donor-acceptor (D-A) materials are designed and synthesized using the tripenylamine-phenanthroimidazole backbone donor and triphenyltriazine as the acceptor, with different distance between the donor and acceptor units. The shorter distanced DRZ-TPM forms a typical CT excited state, and its organic light emitting diode (OLED) produced green electroluminescence with maximum external quantum efficiency (EQEmax) of 5.0%. To regulate the light color, we inserted a phenyl ring to increase the donor-acceptor distance for a reduced CT component. The new material TRZ-TPM achieves sky-blue electroluminescence at 452 nm with EQEmax of 2.5% in doped OLED. Furthermore, TRZ-TPM showed obvious excimer emission in the aggregated state, and the non-doped OLED performed reduced opening-voltage comparing to the doped OLED, owing to the better formation of intermolecular charge-transfer state.