The evident aggregation-induced emission and the reversible mechano-responsive behavior of carbazole-containing cruciform luminophore

Abstract New D-A type cruciform luminophore TFMB-CBCEB bearing electron-donor carbazole unit and electron-acceptor dicyanovinylbenzene segment was designed and prepared. The results show that the emission wavelengths of TFMB-CBCEB are strongly affected by solvent polarity, indicating intramolecular charge-transfer (ICT) transitions. Interestingly, TFMB-CBCEB exhibits AIE behavior with high αAIE of 405 and high solid-state luminescence efficiency of up to 0.810. Moreover, TFMB-CBCEB shows remarkable mechanofluorochromic (MFC) properties. When the as-prepared samples are subjected to grinding, the emission of TFMB-CBCEB red-shifts by 32 nm from the blue regions (λmax = 566 nm) to the orange regions (λmax = 598 nm). The changes of fluorescence emission induced by grinding can be restored by solvent-fuming and regenerated by grinding, suggesting excellent reversibility in the switching processes. PXRD analysis revealed that the MFC mechanism of TFMB-CBCEB attributed to the crystalline-amorphous phase transformation between the original and ground states. Meanwhile, the red-shift in the PL spectra upon grinding comes from the extension in molecular conjugation caused by planarization of molecular conformation and subsequent planar intramolecular charge transfer (PICT) process.