Benzimidazole‐Based Dual‐State Luminophores with Acid Responsiveness and Thermo‐Switchable Emission in Phase‑Change Matrix

Dual-state luminescent materials, which emit strongly in both dispersed and aggregate states, are highly desirable for advanced optoelectronic and sensing applications. In this study, we rationally designed a series of benzimidazole-based donor-π-acceptor (D-π-A) compounds using triphenylamine (TPA) as the donor and benzimidazole as the acceptor, functionalized with flexible alkyl chains to modulate intermolecular packing. Benefitting from their rigid planar molecular conformation, all four compounds exhibit intense blue fluorescence in both solution and the PMMA-doped state. Among them, the highest luminescence efficiencies of the molecule C0 in the DCM- and PMMA-doped films reach 78.72% and 65.28%, respectively. Notably, their PMMA-doped films also exhibit obvious yellowish-green afterglows after 5 s continuous UV irradiation. In the solid state, the chain-free molecule C0 forms a staggered stacking with intermolecular hydrogen bonds, resulting in a bright excimer emission. As the alkyl chain length increases, the added steric bulk gradually suppresses the intermolecular interactions, inducing a significant transition from excimer emission to blue-shifted monomer emission. Furthermore, the nitrogen atom of benzimidazole endows these luminophores with pronounced acid-responsive fluorescence behavior. By exploiting the distinct luminescent contrast between the excimer and monomer emissions of C0, we developed a temperature-responsive fluorescence system through embedding C0 into a phase-change matrix, which enables a reversible thermochromic fluorescence switching. This work provides a valuable strategy for designing dual-state emission and stimuli-responsive benzimidazole-based materials with potential applications in optical sensing and display technologies.