Multicolored-fluorescence switching of ICT-type organic solids with clear color difference: mechanically controlled excited state.

A donor-acceptor-type fluorophore containing a twisted diphenylacrylonitrile and triphenylamine has been developed by using the Suzuki reaction. The system indicates typical intramolecular charge-transfer properties. Upon mechanical grinding or hydrostatic pressure, the fluorophore reveals a multicolored fluorescence switching. Interestingly, a fluorescence color transition from green to red was clearly observed, and the change of photoluminescent (PL) wavelength gets close to 111 nm. The mechanisms of high-contrast mechanochromic behavior are fully investigated by techniques including powder XRD, PL lifetime, high-pressure PL lifetime, and Raman spectra analysis. The tremendous PL wavelength shift is attributed to gradual transition of excited states from the local excited state to the charge-transfer state.