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.