Excellent aggregation-induced emission and mechanofluorochromic performances of donor–acceptor luminophores functionalized with tetraphenylethene

Abstract

Two novel D-A type MFC molecules, BTPEBZBP and BTPECEBP, incorporating tetraphenylethylene units, were synthesized via a unified synthetic route. Both compounds exhibit pronounced ICT characteristics and significant AIE behavior, with AIE factors exceeding 135 and 58, respectively. Notably, they demonstrate exceptional MFC performance. The pristine powders of BTPEBZBP and BTPECEBP display intense blue and yellow-green luminescence, correspondingly. Mechanical grinding causes their luminescence colors to transform to green and orange-red, respectively. The fluorescence peaks exhibit redshifts, shifting from 461 nm to 533 nm–504 nm and 594 nm, accordingly. Additionally, the solid-state emission efficiencies of BTPEBZBP and BTPECEBP notably elevate from 0.135 to 0.174 to 0.175 and 0.385, respectively, upon mechanical stimulation. BTPEBZBP exhibits reversible MFC characteristics when exposed to DCM vapors, while ground BTPECEBP samples transition to Y-powders emitting yellow fluorescence with the wavelength of about 567 nm under DCM vapor fuming, demonstrating three-color fluorescence switching. The MFC properties of both compounds arise primarily from the transformation between crystalline and non-crystalline states. The detected bathochromic shift in PL spectra stems from a decreased bandgap, which results from extended π-conjugation, enhanced PICT effects, strengthened π-π stacking, and elevated exciton coupling coupled with stronger orbital overlap between adjacent molecules.