High Contrast and Bright Emission Piezochromic Fluorescence in Organic Crystals via Pressure Modulated Exciton Coupling Effect

Abstract With its recent debut in various fields, piezochromic fluorescent (PCF) materials have attracted considerable attention due to their unique photophysical features with dynamically reversible emission wavelength and intensity. Herein, a novel luminogen DBCT is developed, which is sensitive to external pressure and displays dual color reversibly switched PCF fluorescence. The solid state emission can switch from bright orange (O) (λ_em = 586 nm, Φ_solid = 0.47) to deep red (R) emission (λ_em = 646 nm, Φ_solid = 0.34) with high contrast through pressing (0.6 MPa), heating and fuming processes. Single crystal X‐ray analysis and theoretical calculations verify that the reversible luminescence switching characteristic is highly related to the different molecular packing mode within O and R crystals, which amplifies the exciton coupling (EC) effect and results in good PCF performances with high Φ_solid as well as distinguishable red‐shifted emission. With such multiple advantages that writable fluorescent inks are successfully fabricated with high contrast for security anti‐counterfeiting applications based on DBCT molecules. This research may offer an important guideline for molecular design of PCF materials and enrich the underlying mechanism of mechanochromic luminescence, which also broadens the real‐life applications of smart materials.