Quantification of Through-Space Intervalence Charge Transfer in Cofacial Thiazolothiazole Metal–Organic Framework and Its Photochromic Behavior

Electronic coupling between individual redox units in a molecular assembly dictates their charge transfer efficacy. Being a well-defined crystalline structure, the metal–organic framework (MOF) ensures proper positioning of redox-active moieties and provides a unique platform to unveil their charge transfer dynamics and quantification with structural relationships. Here, we demonstrate a novel redox-active MOF with near-infrared through-space intervalence charge transfer by introducing a mixed valence state inside redox-active thiazolothiazole-based ligands (DPTTZ) upon photo- or electrochemical reduction. The faster carrier growth and recombination, as well as higher effective mobility in MOF, is attributed to lesser separation between redox-active DPTTZ molecules (3.75 Å) than the bare ligand system (4 Å), which results in higher through-space electronic coupling. The photoreduction ability of the MOF with visible color change was utilized to show photochromic behavior, and further fabrication to a solid-state photochromic device for a potential autodarkening material under UV irradiation was conducted.