Hydrogen-Bonding Induced Multicolor and Thermochromic Emissions of Triphenylamines.

Abstract

The fluorescence tuning of stimuli responsive materials is crucial but challenging, the deep understanding of thermal induced fluorescence change, however, has rarely been conducted. Herein, The thermochromic emission of a triphenylamine (TPA) derivative (1), with one acetyl and two 1-hydroxy-1-methylethyl units on each o-phenyl group around the nitrogen, has been investigated. Upon heating, the bright blue-emitting solid 1 turns to a strong green-emitting liquid. Moreover, 1 is green emissive in ethanol, but blue emissive with high absolute quantum yields in strong hydrogen-bond accepting solvent of dimethyl sulfoxide (DMSO). Another TPA derivative (2), with one 1-hydroxy-1-methylethyl and two acetyl groups on each o-phenyl group, is green emitting. X-ray crystallography studies together with theoretical calculations reveal that the strong solid state fluorescence arises from a rigid pyramidal structure around central nitrogen of 1, due to the OH•••OH, OH•••O=C hydrogen bonding interactions. Comparatively, 2 has a planar configuration of three C-N bonds around central nitrogen atom. This work will provide new route for constructing multi-emission materials using unimolecular platforms.