Afterglow Properties of Zinc Sulfate Open Frameworks: Nonconventional Chromophore Induction and Doping Modulation

Molecular-based afterglow materials are highly attractive, yet nonaromatic room-temperature phosphorescence (RTP) systems remain limited and often suffer from limited emission colors and low efficiency. A rational design to enhance their performance is crucial for their applications. Herein, we report the synthesis of two new inorganic-organic hybrid ZnSO₄ open-framework materials (OFMs), featuring a two-dimensional (2D) anionic layer and a three-dimensional (3D) perovskite-like framework, respectively. Despite lacking conventional luminophores, they exhibit a blue-green afterglow with lifetimes of 382.1 and 325.9 ms, respectively. Frontier orbital analysis reveals significant p-electron delocalization involving O/N atoms within the anionic framework and structure-directing agents, forming spatially extended electron conjugation domains. The rigid ZnSO₄ frameworks suppress molecular motions, stabilizing triplet states. Notably, host-guest doping with phosphorescent guests into these OFMs dramatically enhances RTP. Emission color is tunable from dark blue (430 nm) to orange-red (580 nm), with lifetimes extended to 1.83 s. The stabilization of guest molecules within the rigid host and suppression of aggregation-caused quenching, along with energy transfer and competitive absorption between the host and guest, are identified as crucial factors in enhancing RTP in these systems. This work establishes ZnSO₄ OFMs as promising platforms for nonconventional RTP materials, and the host-guest strategy offers a universal approach for achieving high-performance, color-tunable afterglow.