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

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 pi-pi* 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).