Achieving luminescence with earth abundant metals at room temperature is a difficult task to this day. Minimal overlap between ligand and 3d orbitals means there are more low energy metal centered states which favor non radiative relaxation back to the ground state rather than luminescence. Prior to a 2020 report1 of the vanadium(III) complex mer-[V(ddpd)2][PF6]3 (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-ylpyridine-2,6-diamine) no first row transition metal had been shown to emit light in the near-infrared-II range (1000 – 1700nm) at room temperature. NIR light has many exciting applications such as bioimaging due to deeper tissue penetration, or in telecommunications for optical amplification. In this presentation I will share how the strong field ligand ddpd enables intersystem crossing and subsequent NIR phosphorescence in a vanadium complex. Design principals learned through this example will be discussed for their future use in emissive vanadium complexes as well as first row transition metal complexes with NIR fluorescence.
(1) Dorn, M.; Kalmbach, J.; Boden, P.; Päpcke, A.; Gómez, S.; Förster, C.; Kuczelinis, F.; Carrella, L. M.; Büldt, L. A.; Bings, N. H.; Rentschler, E.; Lochbrunner, S.; González, L.; Gerhards, M.; Seitz, M.; Heinze, K. A Vanadium(III) Complex with Blue and NIR-II Spin-Flip Luminescence in Solution. J. Am. Chem. Soc. 2020, 142 (17). https://doi.org/10.1021/jacs.0c02122.