Tetraphenylimidazole-based excited-state intramolecular proton-transfer molecules for highly efficient blue electroluminescence

Abstract

Aiming for highly efficient blue electroluminesence, we have designed and synthesized a novel class of tetraphenylimidazol-based excited-state intramolecular proton-transfer (ESIPT) molecules with covalently linked charge-transporting functional groups (carbazole- and oxadiazole- functionalized hydroxyl-substituted tetraphenylimidazole (HPI), i.e., HPI-Cbz and HPI-Oxd, respectively). High T-g (ca. 130 degrees C) amorphous films of HPI-Cbz and HPI-Oxd showed and ideal blue-light emission (lambda(max)=462 and 468 nm, Phi(PL) = 0.48 and 0.38) with a large Stokes shift of over 160 nm and a narrow full width at half-maximum of less than 65 nm. Organic light-emitting devices using HPI-Cbz and HPI-Oxd as the emitting layer generated an efficient blue electroluminescence (EL) emission peaking at around 460 nm with excellent CIE coordinates of (x, y) = (0.15, 0.1). A maximum external quantum efficiency of 2.94% and a maximum brightness of 1 229 cd m(-2) at 100 mA cm(-2), as well as a low turn-on voltage of 48.4 V were achieved in this work.