Carbazole-modified fumaronitrile-containing D-π-A-π-D type AIEgen with high-contrast three-color mechanofluorochromism

Anisotropic force-triggered high-contrast tricolored fluorescence molecular switches are promising candidates for high-performance force-dependent multi-signal fluorescence sensors, but the preparation of such smart switches remains highly challenging. Herein, a donor-π-acceptor-π-donor type fluorogenic compound Cz-π-FMN-π-Cz, employing two carbazole groups as donors, four biphenyl groups as π-conjugated spacing moieties, and one fumaronitrile group as acceptor, is skillfully designed and successfully prepared. Interestingly, luminogen Cz-π-FMN-π-Cz demonstrates remarkable aggregation-induced emission phenomenon, and the pristine yellow-green light-emitting powder sample of Cz-π-FMN-π-Cz is changed into yellowish-brown fluorescent solid after slight grinding. Impressively, the yellowish-brown fluorescence triggered by slight mechanical force of solid Cz-π-FMN-π-Cz can be further converted into orange-red fluorescence upon heavy grinding. Powder X-ray diffraction and differential scanning calorimetry techniques are applied to elucidate the possible mechanism of anisotropic force-induced yellow-green–to–yellowish-brown–to–orange-red contrasting tricolored fluorescence property of Cz-π-FMN-π-Cz. Furthermore, an information encryption system based on force-responsive dual-fluorescence sensing feature of Cz-π-FMN-π-Cz is constructed.