Tunable photofluorochromic switch driven by dynamic through-space conjugation

Light is a powerful stimulus for regulating molecular functions, yet achieving precise and efficient photoswitching remains a significant challenge in organic materials, particularly in the aggregate state. Here we report a strategy based on dynamic through-space conjugation (TSC) to regulate photoswitching in Schiff-base crystals. Upon photoexcitation, the system undergoes an excited-state intramolecular proton transfer followed sequentially by cis-trans keto isomerization, a process in which electrons near the nitrogen atom dynamically couple with adjacent π-donors. This transient nitrogen-based TSC, captured by the femtosecond transient absorption spectroscopy and corroborated by high-pressure experiments and calculations, modulates both the transition-state barrier and the stability of the metastable state, thereby markedly enhancing photoswitching efficiency. Beyond mechanistic insight, this study introduces a design paradigm that exploits dynamic nitrogen-based TSC to engineer light-driven logic devices, with broad implications extending from artificial vision sensors to molecular motors.