Tetraphenylethene-containing cruciform luminophores with aggregation-induced emission and mechanoresponsive behavior

Two D-A type cruciform luminophores MODCS-TPE and FMDCS-TPE were successfully prepared via a two-step route involving Suzuki cross-coupling and Knoevenagel condensation reactions, and their intramolecular charge-transfer (ICT) and solid-state fluorescence were studied in detail. The results show that MODCS-TPE and FMDCS-TPE exhibit AIE behavior with high solid state fluorescence efficiency of 0.321 and 0.312. Interestingly, MODCS-TPE and FMDCS-TPE exhibit both typical AIE behavior with the AIE factors of 138 and 51 and high contrast MFC effects. Once grinding had been performed, the emission of the two cruciform luminophores was red shifted by 34 nm and 44 nm from the blue regions (lambda(max) = 471 nm and 478 nm) to the green and yellowish green regions (lambda(max) = 505 nm and 522 nm), respectively. Moreover, the mechanochromic switching behavior was reversible and repeated many times without any fatigue in the grinding-heating (for MODCS-TPE) or grinding-fuming (for MODCS-TPE and FMDCS-TPE) fluorochromic process. The mechanism of MFC behavior that the transformation between crystalline and amorphous states upon external stimuli is revealed by PXRD and DSC analysis, and the large red-shifts induced by grinding originate from extended conjugation and subsequent planar intramolecular charge transfer (PICT) after grinding.