Tuning the dual emission of keto/enol forms of excited-state intramolecular proton transfer (ESIPT) emitters via intramolecular charge transfer (ICT)

Abstract Herein disclosed the adjustment of the dual emission of keto and enol forms of excited-state intramolecular proton transfer (ESIPT) emitters via intramolecular charge transfer (ICT) effects. Introducing electron-donating triphenylamine (TPA) and electron-withdrawing triphenylboron (TPB) substituents into the para-position of the phenolic hydroxyl group or the side of the oxazole of 2-(2′-hydroxyphenyl)oxazole skeleton endows the resulting compounds (6a-6d) with different photophysical properties. Owing to the ICT effect from electronic donor to acceptor, introducing TPA into the side of oxazole and TPB into the para-position of phenolic hydroxyl is conducive to an enol-form emission (6a). Exchanging the two substituents, namely introducing TPB into the side of oxazole and TPA into the para-position of phenolic hydroxyl, would be beneficial to a keto-form emission (6b). Synchronously introducing two identical substituents, whether TPA or TPB, into two sides of 2-(2′-hydroxyphenyl)oxazole skeleton (6c and 6d) would lead to the dual emission of keto and enol forms due to the excited-state equilibrium of ESIPT reactions, which are further verified by DFT calculation. The organic light-emitting diode (OLED) devices with 6a and 6c as emitters were fabricated, both of which exhibit hybridized local and charge transfer (HLCT) excited-state characters with high external quantum efficiencies (EQEs) of 4.9% and 5.6%, respectively.