Aggregation-Induced Emission Enhancement and Solid-State Photoswitching of Crystalline Carbazole <i>N</i>-Salicylidene Anilines

The development of fluorescent stimuli-responsive organic materials has attracted substantial interest due to their increasing optoelectronic applications. This study systematically introduces fluorine atoms on one end of carbazole-based <i>N</i>-salicylidene anilines <b>5a</b>-<b>5f</b> to elucidate the impact in their solution and solid-state photophysics. The addition of fluorine atoms at one end of the molecule induced significant changes, for example, a reduction in the quantum yield (QY) fluorescence emission in solution, going from QY near unity in compound <b>5a</b> (QY ∼ 100%) to a negligible emission in <b>5f</b> (QY < 1%). Similarly, compound <b>5a</b> showed a very strong aggregation-induced enhancement emission behavior, whereas compounds with a higher fluorine content were almost quenched. Furthermore, the crystalline solid-state photoisomerization in <i>N</i>-salicylidene anilines is not trivial, and only compounds with three (<b>5e</b>) and five fluorine atoms (<b>5f</b>) exhibited reversible solid-state photoisomerization under 405 nm light source irradiation. We propose that the presence of the arene-perfluoroarene interaction in the crystalline array facilitates the latter behavior. Our findings present a comprehensive study of crystal engineering for the obtention of photoswitchable crystalline materials and adjustable photophysics response, paving the way for its implementation in other systems.