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Structure-dependent reversible mechanochromism of D-π-A triphenylamine derivatives

Jia, Junhui, Zhao, Haixia
Tetrahedron letters 2019 v.60 no.3 pp. 252-259
Suzuki reaction, color, crystal structure, fluorescence, grinding, isomers, methylene chloride, moieties, optical properties, phase transition
Three simple non-planar D-π-A TPA-based isomers (TPA-o, TPA-m, and TPA-p) were designed and synthesized via Suzuki reaction with higher yields. It was found that all of the three compounds had intramolecular charge transfer (ICT) properties resulting from electron donation from triphenylamine to the formyl moiety. Interestingly, TPA-based derivatives solids exhibited not only reversible mechanochromic behaviors, but structure-dependent emission properties. The solid emission studies illustrated that their fluorescence color could change reversibly between bright blue (455 nm), blue (445 nm), cyan (479 nm), and bright blue-green (497 nm), bright blue (460 nm), yellowish-green (511 nm) through grinding and dichloromethane (DCM) fuming treatment, giving the large spectral red-shifts of 42, 15, and 32 nm, respectively. The MFC activities of the three compounds are increased with the sequence of TPA-o (42 nm) > TPA-p (32 nm) > TPA-m (15 nm). The single crystal structure, powder X-ray diffraction (PXRD) and DSC studies indicated that the reversible phase change from crystalline to amorphous was responsible for MFC properties. This work demonstrated the feasibility of tuning the solid-state optical properties of fluorescent organic compounds by combining the simple alteration of chemical structure and the physical change of aggregate morphology under external stimuli. And these results will be of great help in understanding structure-property relationships of MFC mechanisms and designing new more MFC materials.