Anion–π(–π) Interactions in Donor–Acceptor Hybrid Materials to Control Photochromism and Room-Temperature Phosphorescence

Abstract

Photochromic materials and room-temperature phosphorescence (RTP) are essential for applications in optoelectronics and bioimaging. Organic–inorganic hybrid materials, particularly those exhibiting donor–acceptor (D–A) characteristics through supramolecular interactions, have shown significant potential to integrate both photochromic and RTP properties. Among them, the anion–π and π–π interactions have been extensively studied; however, the role of anion–π–π interactions in hybrid materials remains largely unexplored. This study investigated three naphthalenediimide-polyoxometalate (NDI-POM) hybrids: (H₂DMAP-NDI)·(HPW₁₂O₄₀)·(NMP)₂ (1), (HDMAP-NDI)₂·(HPW₁₂O₄₀)·(NMP)₂ (2), and (HDMAP-NDI)₂·(HPW₁₂O₄₀)·(NMP)₇ (3), focusing on the impact of anion–π–π interactions on their photochromic and RTP properties. The results indicate that hybrid 1 exhibits the fastest photoresponse and highest RTP quantum yield, primarily driven by anion–π interactions. Hybrid 2, which involves anion–π–π interactions, shows slower photochromism and lower RTP yield due to exciton localization and nonradiative decay paths resulting from π–π stacking. Hybrid 3, characterized by excessively strong interactions, is unstable and nonemissive. This study provides valuable insights into the role of anion–π–π interactions in hybrid materials and offers a framework for designing advanced photoresponsive materials with tunable properties for diverse applications.