Tunable NIR absorption in gold complexes with mixed dithiolene/diselenolene ligands

Based on a step-by-step procedure, an extensive series of monoanionic d 8 gold complexes has been developed by replacing in mixed-ligand bis(dithiolene) complexes the coordinating sulfur atoms by selenium ones, either on one ligand or on both, leading to very original and stable mixed-ligand gold (dithiolene)(diselenolene) and bis(diselenolene) complexes. The neutral radical species obtained upon 1e – oxidation of bis(dithiolene) gold complexes are known to exhibit an NIR absorption band in the 1180−2070 nm range, of interest in telecommunications, biological imaging and solar cells. Here, spectroelectrochemical investigations demonstrate that the NIR signature of mixed-ligand bis(dithiolene), (dithiolene)(diselenolene) and bis(diselenolene) gold complexes associating two different dithiolene or diselenolene ligands is found at higher energy, out of the range of the homoleptic analogs. Moreover, introduction of Se atoms on the more electron-rich ligand modifies significantly the LUMO of the complex, leading to a further 200 nm bathochromic shift of this characteristic NIR absorption, thus offering an additional control of the NIR absorption of these neutral radical gold complexes. The preparation of mixed ligand gold complexes, dithiolene and diselenolene, enables extra control over NIR absorption. • Performance of the strategy for the synthesis of gold dithiolene/diselenolene complexes • Gold mixed ligands complexes as NIR absorbers • Electron-rich and electron-poor ligands enable control of absorption in the near infrared. • Additional control of NIR absorption through the introduction of a diselenolene ligand