Design, synthesis, and mechanochromic luminescence of twisted donor–acceptor bisarylic methanone derivatives

Two bisarylic methanone derivatives, DBF-BZ-POZ and DBF-BZ-PTZ , which have phenoxazine or phenothiazine as electron donors and carbonyl group as electron acceptor are presented. Both molecules have highly distorted molecular conformation and exhibit obvious intramolecular charge transfer (ICT), effective solid-state emissions, and high-contrast mechanofluorochromic (MFC) properties. Both DBF-BZ-POZ and DBF-BZ-PTZ have good solid-state luminescence, efficiencies that reach 33.5% and 38.9%, respectively. The fluorescence colors of the as-prepared powders for both molecules are bright blue-green. The colors change to bright yellow with external mechanical stimulation and red shifts of 104 and 82 nm are observed in the photoluminescence (PL) spectra. Moreover, the MFC behavior of DBF-BZ-POZ and DBF-BZ-PTZ are reversible when their ground samples are subjected to fuming with the DCM vapor. Powder X-ray diffraction results indicate that the MFC phenomenon of DBF-BZ-POZ and DBF-BZ-PTZ may be attributed to crystalline-to-amorphous transitions in the material. The red shifts observed in the PL spectra after the material is ground are due to the smaller band gap induced by the planar intramolecular charge transfer (PICT) and the increased π-π interactions, the increase of exciton coupling, as well as the increased orbital overlap between neighboring molecules. • Two bisarylic methanone derivatives showing highly distorted molecular conformations were synthesized. • The two compounds possess good solid-state emissions with luminescence efficiencies of 33.5% and 38.9%, respectively. • The two compounds exhibit reversible MFC behavior with large red shifts of 104 and 82 nm in PL spectra, respectively.