Reversible solid-state mechanochromic luminescence originated from aggregation-induced enhanced emission-active Donor−Acceptor cruciform luminophores containing triphenylamine

Abstract

Two D-A type cruciform luminophores FB-CTPAEB and DFB-CTPAEB were designed and prepared. The two compounds exhibited unique intramolecular charge-transfer (ICT) and solid-state fluorescence behavior. The results show that both compounds exhibit AIEE behavior and high solid-state luminescence efficiency (up to 0.693 and 0.442, respectively). Moreover, FB-CTPAEB and DFB-CTPAEB show remarkable mechanofluorochromic (MFC) properties. Once the as-prepared samples were subjected to grinding, the emission of the two cruciform luminophores was red shifted by 52 nm and 46 nm, correspondingly, their fluorescence colors changed from yellow and reddish orange to red, respectively. The fluorescence emission changes induced by grinding can be restored by solvent-fuming and regenerated by grinding. PXRD analysis revealed that the MFC behavior of FB-CTPAEB and DFB-CTPAEB came from the transformation between crystalline and amorphous states upon external stimuli. Meanwhile, the extension in molecular conjugation caused by planarization of molecular conformation and subsequent planar intramolecular charge transfer (PICT) process were responsible for the red-shifts in the PL spectra.