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

Abstract

A series of luminescent Cu(I) complexes incorporating the N,N-diphenylpyridin-4-amine (DPPA) and PPh<inf>3</inf> were synthesized and characterized, revealing intriguing photophysical and stimuli-responsive properties. Single-crystal X-ray diffraction studies confirmed the formation for [Cu<inf>2</inf>X<inf>2</inf>(DPPA)<inf>2</inf>(PPh<inf>3</inf>)<inf>2</inf>] (X = I, Br, Cl for C<inf>1</inf>, C<inf>2</inf>, and C<inf>3</inf>) having Cu<inf>2</inf>X<inf>2</inf> rhomboid core. These complexes exhibit intense blue to cyan-blue solid-state emission, with λ<inf>em</inf> at 436 (C<inf>1</inf>), 462 (C<inf>2</inf>), and 491 nm (C<inf>3</inf>). Remarkably, C<inf>2</inf> and C<inf>3</inf> 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 (C<inf>1</inf>: 436 nm → 502 nm

C<inf>2</inf>: 462 nm → 531 nm

C<inf>3</inf>: 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. © 2026 Wiley-VCH GmbH.