“In the field of molecular fluorescence, researchers have synthesized a perylene diimide derivative, PDI-COOH, which exhibits significantly enhanced fluorescence when combined with calcium ions in THF/H2O solution. By altering hydration levels and concentrations, the assembly and fluorescence behavior of PDI-COOH/Ca2+ were studied, leading to the proposal of a fluorescence emission mechanism. This work highlights a novel strategy for aggregated state fluorescence enhancement and underscores the crucial role of water in molecular fluorescence emission and assembly.”