High Photothermal Activity within Neutral Nickel Dithiolene Complexes Derived from Imidazolium-Based Ionic Liquids

A new series of nickel N,N′-dialkylimidazolidine-2,4,5-trithione complexes ([Ni­(R2timdt)2]) carrying linear or branched carbon chains (R = n-C4H9, n-C8H17, n-C12H25, n-C16H33, 2-ethylhexyl, 2-butyloctyl, phytanyl) have been obtained through an original synthetic pathway starting from easily available imidazolium-based ionic liquids. The chemical structures of these nickel complexes were confirmed by NMR and high-resolution mass spectroscopies as well as by X-ray analysis performed on single crystals. The complexes strongly absorb in the near-IR (NIR) region around 1000 nm, with high extinction coefficients reaching 80 000 M–1 cm–1. They are able to efficiently convert NIR light into heat under laser irradiation with very high photothermal conversion efficiencies (around 30%).