Triphenylamine-imidazole-based luminophores for deep-blue organic light-emitting diodes: experimental and theoretical investigations

Abstract

In this paper, three deep blue donor–acceptor (D–A) luminophores with triphenylamine as the hole-transporting system and imidazole as the electron-transporting system were synthesized by a condensation reaction and characterized by spectroscopic methods. The detailed thermal, optical, electrochemical and electroluminescence properties were systematically investigated. The synthesized luminophores exhibited good thermal stability and a good photoluminescence quantum yield (PLQY). The ultraviolet-visible (UV-vis) spectra of the luminophores showed multiple absorption bands (UV to near UV region, due to the π–π* transitions of the aromatic segments). All the luminophores exhibited blue emission in a dichloromethane (DCM) solution. Solution-processable OLEDs were fabricated by using these luminophores as an emitting dopant in the 4,4′-bis(9H-carbazol-9-yl)biphenyl host and they were found to exhibit bright deep blue electroluminescence (EL). Among these luminophores, the one donor–two acceptor (DBIPTPA) luminophore displayed promising deep blue emission characteristics with more than 100% color saturation when compared with the National Television System Committee (NTSC) standard. The device fabricated using DBIPTPA showed a high luminance of 495 cd m⁻² and 2.5% external quantum efficiency with the CIE coordinate of (0.16, 0.06) at the brightness of 100 cd m⁻².