Cyano-substituted triphenylamine derivative with mechanochromism and mechanoluminescence

To achieve materials exhibiting both mechanoluminescent and mechanochromic activities, an asymmetrical triphenylamine derivative, DCTPAA, containing one aldehyde group and two cyano groups, was designed and synthesized. DCTPAA displayed solvatochromism, with a red-shifted emission as the solvent polarity increased, indicating the donor-acceptor structure's inherent property. It emitted blue fluorescence in its pristine crystal state, but exhibited green fluorescence upon grinding. The blue fluorescence could be restored after the ground powder was treated with dichloromethane vapor, showcasing reversible mechanochromism. The X-ray diffraction pattern suggested that the mechanochromic process was accompanied by a reversible phase change between the crystalline and amorphous states. Notably, despite the centrosymmetric space group of the DCTPAA crystal, the material displayed strong mechanoluminescence emission. The intermolecular packing analysis and theoretical calculations demonstrated that the strong intermolecular interaction should contribute to the mechanoluminescence.