Dibenzo[a,c]phenazine-phenothiazine dyad: AIEE, polymorphism, distinctive mechanochromism, high sensitivity to pressure

Abstract Herein, we report a new dibenzo[a,c]phenazine-phenothiazine dyad (BNPTZ) bridged by a C–N single bond, which realizes AIEE, polymorphism, mechanochromsim and high sensitivity to hydrostatic pressure, due to the twisted D-A structure. BNPTZ exhibits AIEE activity in THF/H2O system, owing to aggregation-inhibited non-radiative relaxation channels of the excited states. Fortunately, two types of single crystals of BNPTZ with distinctive luminescence were cultivated and the effect of different conformation and complicated intermolecular interactions on luminescent property was analysed. BNPTZ demonstrates responses to both shearing force and hydrostatic pressure. Interestingly, two different crystalline phases are involved in the color-changing process upon shearing and fuming. Upon shearing, the crystal powder suffers the luminescence color change from orange-yellow (565 nm) to redness (604 nm), because of the phase transition from OY-phase to amorphous triggered by external force. When fuming, the amorphous phase would recover to YG-phase unexpectedly. When subjecting two single crystals to hydrostatic pressure, the OY-phase single crystal underwent a clear color switch from yellow to orange and eventually to red. The YG-phase single crystal displayed a different color alteration from yellow-green to orange and further to red. Both of the two single crystals exhibited relatively high sensitivity to pressure with a wide spectral shift over 100 nm. Up to now, BNPTZ is a rare dyad that achieves polymorphs with high sensitivity to pressure.