Electron-Transfer-Mediated Dynamic Control of Photochromism and Fluorescence/Phosphorescence in a Smart Metal–Organic Framework

Smart materials whose color and luminescence can be simultaneously tuned by external stimuli are highly desirable for advanced optical and information technologies. Achieving independent yet coupled control over both photochromism and emission, particularly a dual fluorescence-phosphorescence output, remains difficult, often hampered by poor electronic communication between functional units. We address this challenge with a new metal-organic framework, (H₃-TPB)₂·Zn₄(C₂O₄)₆·SO₄. Its structure combines an oxalate-zinc photochromic layer as an electron donor with freely incorporated protonated 1,3,5-tris(4-pyridyl)benzene ligands, which act as electron acceptors and emitters. This design enables reversible ligand-to-ligand electron transfer upon light exposure, triggering a fast color change from orange-red to purple-black. Under 270 nm excitation, the material displays tunable dual emission. The fluorescence/phosphorescence intensity ratio and the overall emission color can be reversibly switched between violet and white through photoinduced radical formation and subsequent thermal elimination. These properties are successfully applied to high-resolution ink-free printing and dynamic information encryption. Our work demonstrates a general electron-transfer approach to create multimodal photoactive materials with synchronized and reversible optical responses.