Modulation of mechanofluorochromism based on carboxylic acid esters compounds bearing triphenylamine and pyrene with different substituents

Two new three-armed and four-armed carboxylic acid esters derivatives TPT and TBT have been developed and characterized. The two D-A type compounds (different substituents including triphenylamine and pyrene) exhibit intramolecular charge transfer (ICT) emission process from electron donor (aromatic group) to electron-withdrawing (methyl naphthoate moiety). Interestingly, it was found that TPT and TBT exhibit reversible mechanofluorochromic (MFC) properties with fluorescence color switches from initial cyan and bright yellow light to final bright yellow emissions under mechanical force stimuli. Upon the treatment of grinding, heating or exposure to organic vapor, the emission peak of TPT in as-synthesized solid powder exhibited bathochromic shift from 472 nm to 499 nm, but TBT showed hypsochromic shift from 541 nm to 498 nm, respectively. The X-ray diffraction and DSC measurements suggested that the MFC-chromism of TPT and TBT originated from the reversible different phase morphs between the crystalline (ordered accumulation) and amorphous states (disordered accumulation). The mechanochromic mechanism was given based on the spectral results. Therefore, the carboxylic acid esters derivatives might have potential applications in mechanofluorochromic materials.