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

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 (<b>1</b>), (HDMAP-NDI)₂·(HPW₁₂O₄₀)·(NMP)₂ (<b>2</b>), and (HDMAP-NDI)₂·(HPW₁₂O₄₀)·(NMP)₇ (<b>3</b>), focusing on the impact of anion-π-π interactions on their photochromic and RTP properties. The results indicate that hybrid <b>1</b> exhibits the fastest photoresponse and highest RTP quantum yield, primarily driven by anion-π interactions. Hybrid <b>2</b>, 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 <b>3</b>, 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.