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.