Solvent-Induced Diversified Assembly of Crystalline Materials for Dynamically Switchable Optical Modulation

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Herein, two distinct crystals from the same precursors by modulating the solvent ratio in solvothermal reactions were successfully obtained. Comprehensive characterization, including single-crystal X-ray diffraction, solid-state UV–vis-NIR diffuse reflectance spectroscopy, electron paramagnetic resonance, powder X-ray diffraction (PXRD), and theoretical calculations, provided deep insight into the material’s unique structure and electronic characteristics. The results revealed that Crystal 1 exhibits a unique structure comprising alternating metal-oxo clusters and organic linkers, reinforced by strong lone pair−π interactions and a hydrogen-bonding network involving dimethylammonium cations. These structural features endow this crystalline material with broad-range absorption (200–850 nm) and a narrow bandgap (as small as 1.55 eV). Remarkably, Crystal 1 enables efficient and reversible switching between black and yellow states through alternating ozone oxidation and photoinduced stimulation, while fully maintaining the integrity of its crystal structure. In contrast, Crystal 2, which lacks such structural motifs, counter cations, and strong intermolecular interactions, shows only narrow and weak absorption with essentially no color change under photoinduction. This work highlights the critical role of targeted intermolecular interactions in directing structure assembly and tuning optoelectronic properties, providing a strategic guideline for the design of intelligent optoelectronic materials.