Achieving blue-shifted mechanofluorochromism via through-space conjugation decoupling

Mechanofluorochromic (MFC) materials that exhibit blue-shifts under mechanical stimuli are highly desirable, yet extremely rare, as most reported systems undergo bathochromic shifts due to force-induced planarization and enhanced π-π interactions driven by through-space coupling (TSC), wherein adjacent chromophores overlap via spatial proximity rather than covalent bonding. This has emerged as a powerful concept to explain and enable emission in clustering-triggered emission (CTE) systems. In these contexts, strengthening intermolecular through-space interactions extends the effective conjugation length, thereby lowering the excited-state energy and promoting red-shifted emission. However, the prevailing paradigm has been exclusively to strengthen such interactions; the reverse strategy-deliberately disrupting them-remains entirely unexplored. Herein, we report a general molecular design strategy termed "through-space conjugation decoupling (TSCD)" to achieve robust blue-shifting fluorescent MFC materials. Guided by three synergistic design criteria, we synthesized a series of D-π-A fluorescent small molecules (Z2-Z6) that achieved efficient dual-state emission. Notably, compound Z3 emits at 637 nm with an exceptionally high PLQY of 39.77% in its crystalline state and undergoes a remarkable blue-shift of 45 nm to 592 nm upon grinding. Systematic mechanistic studies combining X-ray diffraction, time-resolved photoluminescence and theoretical calculations confirm that the crystalline-to-amorphous transition disrupts the through-space conjugation, thereby widening the energy gap. This work establishes a rational paradigm for the design of next-generation blue-shifting MFC materials.