A Near-Infrared-II Emissive Chromium(III) Complex.

The combination of π-donating amido with π-accepting pyridine coordination units in a tridentate chelate ligand causes a strong nephelauxetic effect in a homoleptic Cr complex, which shifts its luminescence to the NIR-II spectral range. Previously explored Cr polypyridine complexes typically emit between 727 and 778 nm (in the red to NIR-I spectral region), and ligand design strategies have so far concentrated on optimizing the ligand field strength. The present work takes a fundamentally different approach and focusses on increasing metal-ligand bond covalence to shift the ruby-like E emission of Cr to 1067 nm at 77 K.