Planarized intramolecular charge transfer on triphenylamine-modified pyrazine and their application in organic light-emitting diodes

Excellent luminescence and transportation are the most essential features of organic light-emitting diodes (OLEDs); however, many D–A type materials usually facilitate charge transport but have poor luminescence properties. Herein, we designed two triphenylamine-pyrazine compounds, namely 25-TPA2P and 26-TPA2P, with planarized intramolecular charge transfer character to overcome this problem. Both single crystal XRD and computational analysis show an asymmetric configuration for 26-TPA2P, which furnishes 26-TPA2P with relatively strong ICT and better charge transport balance, as compared with the symmetric 25-TPA2P. A non-doped device containing 25-TPA2P displays sky-blue electroluminescence with a maximum external quantum efficiency (ηext) of 6.09%, by virtue of its strong emission in the solid state and its orientation; for 26-TPA2P, a deep blue OLED with a CIEy of 0.07 and ηext of 4.88% is achieved. Thanks to the balanced transport ability of 26-TPA2P, a series of high efficiency orange/red phosphorescent OLEDs and two-color hybrid WOLEDs are obtained based on 26-TPA2P as the host material. The ηext of the orange OLED exceeds 28%, and the warm-white OLED exhibits a total ηext of 30.11%. These results suggest that PLICT materials could satisfy both conditions of good charge transportation and luminescence, which could bring about bright prospects for displays and illuminations.