Colour-tunable dual-mode afterglows and helical-array-induced mechanoluminescence from AIE enantiomers: Effects of molecular arrangement on formation and decay of excited states

Dual-mode persistent luminescence and helical-array-induced mechanoluminescence (ML) are observed for the first time from two different polymorphs (SCp and SCb) of a pair of AIE-active enantiomers, respectively. The impressive afterglows from the SCp crystals of (R)-ImNCz and (S)-ImNCz are composed of persistent thermally activated delayed fluorescence and ultralong organic phosphorescence, and their colours can be tuned from yellow to sky blue by temperature in a mild window from 0 °C to 100 °C. In particular, the SCp crystals of (S)-ImNCz present relatively stable warm-white afterglows at around room temperature. The generation of dual-mode persistent luminescence from SCp crystals is probably associated with the charge separation and recombination as well as the small ΔEST values of enantiomer molecules and the strong intermolecular interactions in crystal structures. On the other hand, the conspicuous ML of (R)-ImNCz and (S)-ImNCz from SCb crystals likely results from their helical arrays and notable AIE properties, enabling the formation of crystals with polar space groups and high fluorescence quantum yields. The results from this polymorphic system may provide useful guidance for the development of new organic emitters with innovative applications.