Phenothiazine and diphenylsulfone-based donor-acceptor π-systems exhibiting remarkable mechanofluorochromism

Two donor-acceptor luminophores PTZ-DPS and BPTZ-DPS, which are constructed by electron-donor phenothiazine and electron-acceptor diphenylsulfone moiety, are designed and synthesized. Through the effective combination of phenothiazine and diphenylsulfone unit, PTZ-DPS and BPTZ-DPS molecules adopt twisted molecular conformation, unique intramolecular charge transfer (ICT) behavior and intense fluorescence in both solution and solid state. The solid-state luminescence efficiencies of the two luminophores reach 32.84% and 39.69%, respectively. It is particularly noteworthy that both PTZ-DPS and BPTZ-DPS exhibit switchable mechanofluorochromism with high contrast. Upon external force stimulation, the fluorescence colors of the PTZ-DPS and BPTZ-DPS solid powders that change dramatically from initial bright green and yellow to orange, respectively, are observed. Meanwhile, the emission bands red shift from 499 nm to 564 nm-589 nm and 592 nm, respectively, suggesting the large spectral red shifts of 90 nm and 28 nm. Moreover, the mechanofluorochromic (MFC) behavior of PTZ-DPS and BPTZ-DPS also show good reversibility when fume the ground powders by DCM vapor. PXRD and spectral data suggest that the phase transition between crystalline to amorphous states is responsible for MFC behavior of PTZ-DPS and BPTZ-DPS, and the red-shift in the PL spectrum upon grinding originates from the planarization of the molecular conformation and subsequent planar intramolecular charge transfer (PICT).

Automated summary

Two donor-acceptor luminophores PTZ-DPS and BPTZ-DPS, designed with phenothiazine and diphenylsulfone units, exhibit twisted molecular conformation, unique intramolecular charge transfer behavior, and intense fluorescence. They show switchable mechanofluorochromism, high solid-state luminescence efficiencies, and large spectral red shifts. The mechanofluorochromic behavior is due to phase transition between crystalline to amorphous states.