Isostructural Transformation and Pressure‐Induced Luminescence Activation With Blue‐Shifted Enhancement in Hybrid Copper Halides

ABSTRACT Organic–inorganic metal halides (OIMHs) are tunable and structurally diverse optoelectronic materials, yet some remain non‐ or weakly emissive states under ambient conditions, hindering practical applications. Here, we report a unique first observation of dual‐mode luminescence activation in a new copper halide, (4‐ClBTP) 2 (Cu 2 Br 4 ) (compound 1 , Cu─Br), which switches from a dark to bright emissive state through either solvent‐assisted isostructural transformation or hydrostatic pressure stimuli. Isostructural transformation yields (4‐ClBTP) 2 (Cu 2 I 4 ) (compound 2 , Cu─I), reducing bond angle distortion and enhancing cuprophilic interactions to suppress nonradiative decay. Both compounds 1 (Cu─Br) and 2 (Cu─I) exhibit striking pressure‐induced luminescence activation and blue‐shifted enhancement. This blue‐shift enhancement arises from strengthened through‐space charge transfer (TSCT), facilitated by hydrogen bonding and van der Waals interactions, which outcompetes cuprophilic interactions and elevates the singlet (S 1 ) and triplet (T 1 ) excited‐state energies. This discovery provides a new paradigm for stimuli‐responsive and tunable luminescent systems, revealing fundamental structure‐property relationships in copper halides with broad potential for multifunctional applications.