Hydrogen Bonding-Induced Multicolor and Thermochromic Emissions of Triphenylamines

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 atom, 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 dimethyl sulfoxide (DMSO). Another TPA derivative (2) is green emitting. X-ray crystallography studies 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 a new route for constructing multiemission materials using unimolecular platforms.