Reversible piezochromic luminescence of 9,10-bis[(N-alkylcarbazol-3-yl)vinyl]anthracenes and the dependence on N-alkyl chain length

Aggregation-induced emission-active 9,10-bis[(N-alkylcarbazol-3-yl)vinyl]anthracenes (ACZn) with different length of N-alkyl chains have been designed and synthesized to systematically investigate the effect of chain length on the solid-state fluorescence properties. The results show that these materials exhibit not only reversibly pronounced red shift piezofluorochromism (PFC), but also chain length-dependent fluorescence properties. The solid-state fluorescence efficiencies are decreased upon grinding or with the increase of N-alkyl chain length. Meanwhile, the emission spectra of pristine and ground solids are respectively red-shifted and blue-shifted with the increase of N-alkyl chain length. The shorter the N-alkyl chains, the more remarkable the PFC behaviour of ACZn. Powder X-ray diffraction and DSC experiments reveal that the transformation between crystalline and amorphous states upon external stimuli is responsible for the PFC and restoration behaviours.