New symmetrical and unsymmetrical nickel-dithiolene complexes useful as near-IR dyes and precursors of sulfur-rich donors

Novel symmetrical and unsymmetrical nickel dithiolene complexes based on a new ligand R(2)timdt (the -1 charged 1,3-dialkylimidazolidine-2,4,5-trithio ne) and dmit or rant (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolite; mnt = mi leonitriledithiolate) useful as NIR-dyes and electrochromic materials in th e 880-1400 nm region are described here. The R-2 timdt ligand, where N-elec tron donor atoms of the imidazoline ring are forced into co-planarity with the dithiolene ring, revealed to be valuable in shifting the low energy tra nsition typical of this class of complexes in a region of remarkable intere st for near-IR dyes, while stability was maintained. The symmetrical neutra l complexes absorb very strongly at approximately 1000 nm, region of specia l interest for NIR-dyes in order to be used in Q-switching Neodymium lasers , which operate at 1064 nm. Moreover these complexes work as switchable NIR -dyes, since the absorption is shifted to approximately 1400 nm on reversib le reduction. In the unsymmetrical nickel-dithiolene complexes involving bo th the Pr(2)(i)timdt and dmit or runt ligands a tuning of the NIR-absorptio n depending on the combination of the ligands and of the charge is achieved .