Tunable Phosphorescence in Metastable CuI Assemblies Prepared by Acid‐Fueled Crystal‐to‐Crystal Conversion

Abstract

AbstractAcid acts as a “fuel” in driving kinetic self‐assembly, with crystals of the CuII complex ([CuIICl2(BH)2], BH=benzothiadiazole helicene derivative) being successfully converted to crystals of 1 ([H2BH][CuBr3]) and 2 ([H2BH][CuBr3⋅2H2O]). The metastable features of 1 and 2 enable CuI guest release, with transformation into a thermodynamically favorable form 3 (H2BH⋅2Br). Compound 1 exhibits dual phosphorescence at 452 nm (3MC) and 709 nm (3CT) at room temperature. At lower temperatures, the 3CT band disappears and the 3MC band weakens, while a new emission band at 621 nm (3ππ*) is enhanced. In 1, the subtle structural change and significant emission change depending on temperature is reversible. In contrast, 2 exhibits only 3MC emission at room temperature, with less efficient triplet‐triplet energy transfer (TTET) below 250 K, and with residual 3ππ* emission occurring upon returning to room temperature, even after one week.