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. Photoresponsive materials are promising for functional organic materials though it is challenging to achieve efficient photoswitching. Here the authors harness through-space conjugation to regulate the photoresponse in in Schiff-base crystals.