Diphenylpyridyl Amine Substituted Phosphorescent Cu(I)‐Halide Complexes: Reversible Mechanochromism and Aggregation‐Induced Emission Properties

A series of luminescent Cu(I) complexes incorporating the N,N-diphenylpyridin-4-amine (DPPA) and PPh₃ were synthesized and characterized, revealing intriguing photophysical and stimuli-responsive properties. Single-crystal X-ray diffraction studies confirmed the formation for [Cu₂X₂(DPPA)₂(PPh₃)₂] (X = I, Br, Cl for C₁, C₂, and C₃) having Cu₂X₂ rhomboid core. These complexes exhibit intense blue to cyan-blue solid-state emission, with λ_em at 436 (C₁), 462 (C₂), and 491 nm (C₃). Remarkably, C₂ and C₃ show high photoluminescence quantum yields (PLQY) of 65% and 48%, respectively. Temperature-dependent photoluminescence and lifetime studies suggest phosphorescence. Additionally, these complexes exhibit reversible mechanochromic properties: grinding induces a significant red-shift in emission (C₁: 436 nm → 502 nm; C₂: 462 nm → 531 nm; C₃: 491 nm → 540 nm). The reversible mechanochromism is attributed to the loss in crystallinity and disruption of weak C─H⋯π interactions. The complexes also demonstrate pronounced aggregation-induced emission (AIE) behavior in DMSO/water mixtures, with a significant increase in emission at 90% water fraction. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) analyses revealed the formation of spherical nanoaggregates. These results demonstrate the potential of DPPA-based Cu(I) complexes as stimuli-responsive materials for various applications.