High-contrast and reversible mechanochromic luminescence of a D-π-A compound with a twisted molecular conformation

By integrating a triphenylamino donor (D) and a (2,2-dicyanovinyl) phenyl acceptor (A) with an anthryl pi-spacer, a mechanochromic luminescent (ML) D-pi-A compound, TPAANDCV, has been constructed. The single crystals of TPAANDCV display efficient green emission with a good fluorescence quantum yield (Phi(F)) of 0.35. Upon grinding the crystals, a dramatic emission-colour variation from green to orange-red has been observed, and such a variation can be erased through annealing or solvent-vapour fuming. Moreover, the emission of the ground sample is also bright with a Phi(F) value of 0.11. The powder XRD measurements indicate that the emission-colour change upon grinding is caused by a partial conversion of the ordered solid-state structures to an amorphous state. The high-contrast and reversible fluorescent response of TPAANDCV towards mechanical stress, as well as the bright emission of both the unground and ground states, enable TPAANDCV to be a good ML material.