Efficient Photothermal Energy Conversion Triggered by near-Infrared Light in a Dithiolene-Based Metal–Organic Framework

A Ni-dithiolene ligand, {Ni(pedt)2}− (pedt = 1-(pyridine-4-yl)ethylene-1,2-dithiolate), was used to prepare a novel interpenetrated redox-active Metal–Organic Framework (MOF), which exhibited an efficient photothermal conversion under low-power-density near-infrared (NIR) laser illumination. Solid-state UV–vis-NIR spectroscopy on bulk crystals indicated strong absorbance in the NIR region, attributed to the radical monoanion of the pedt ligands, which was also evident in the solid-state Electron Paramagnetic Resonance (EPR) spectrum. DFT computations on a model system provided new insights into the structural factors underpinning the photothermal properties. First, the NIR absorption corresponds to a high-energy excited state (D4), while the lowest-lying excited state (D1) is close in energy to the energies of the vibrational motions, facilitating the conversion of electronic to thermal energy. Second, close contacts between interpenetrated nets of the MOF may further enhance the propagation of thermal motion. The new photothermal MOF was then doped into a self-healing polymer, PDU (polydimethylsiloxane-urea), leading to composites which could recover from dynamic damage using the heat generated from the embedded MOF by photostimulus. This process led by the photothermal effect offers a highly efficient and energy-saving approach for self-healing materials design.