Solvent-induced crystal engineering for enhanced room-temperature phosphorescence in copper(i) iodide clusters

Based on crystalline polymorphism, we utilized a solvent-mediated crystal engineering strategy to synthesize three polymorphic copper-iodide clusters, 1 [Cu₄I₄(4-dpda)₄], 1-Tol [Cu₄I₄(4-dpda)₄·C₇H₈], and 1-PX [Cu₄I₄(4-dpda)₄·C₈H₁₀] (4-dpda = 4-(diphenylphosphino)-N,N-dimethylaniline), respectively. The polymorphic clusters not only exhibit significant differences in their crystal structures but also manifest remarkable changes in their room-temperature phosphorescence (RTP), high energy (HE)/low energy (LE) energy transfer barriers, and thermal quenching properties. Through comprehensive analysis of the single crystal structure, spectroscopic measurements and theoretical calculation, we elucidated the distinct mechanisms by which solvent-mediated crystal engineering enhances RTP performance. Furthermore, based on the significantly enhanced thermochromic effect, the potential of 1-Tol as a luminescent thermometer with dual-temperature-zone response characteristics was explored, achieving a notable improvement in sensitivity in the low-temperature region. In contrast, 1-PX broadened the response range of thermochromic sensing.