A-π-D-π-A carbazole derivatives with remarkable solvatochromism and mechanoresponsive luminescence turn-on

Two A-pi-D-pi-A molecules with a carbazole donor and a dicyanovinyl acceptor but differing in N-hexyl (h-CPDM) and N-isooctyl substituents (i-CPDM) were synthesized, and both of them presented remarkable dual properties of solvatochromism and mechanoresponsive luminescence (MRL) turn-on. The intrinsic intramolecular charge transfer (ICT) characteristic endowed both luminophors with a prominent solvatochromic effect, with emission color tuning from blue to orange-red by changing the solvent from nonpolar hexane to polar dimethyl sulfoxide. Meanwhile, the non-/weakly emissive original powders of h-CPDM and i-CPDM gave bright orange (610 nm) and yellow (596 nm) emission with the photoluminescence quantum yields increasing as high as 85-fold after being ground. Investigations revealed this mechanoresponsive luminescence turn-on could be ascribed to the disturbance of the p-p stacking interactions in the non-/weakly emissive J-aggregates by mechanical force. This work offers carbazole derivatives that can be used as sensitive fluorescent indicators for organic solvents and mechanical sensors.