Design Of Earth-Abundant W(0) Complexes For Near-Infrared Absorbance Via Ligand Optimization

This work focuses on developing new earth-abundant metal complexes to be used as eAicient near-infrared (NIR) absorbers and photosensitizers for applications in photocatalysis, bioimaging, and photodynamic therapy. By modifying ligand types coordinated to a W(0) center, we aim to enhance NIR absorption and reduce nonradiative decay pathways in turn. Through collaboration with experimentalists in Dr. Wenfang Sun’s group, they were able to synthesize new W(0) complexes coordinated with four carbonyl’s and one 2-(pyrid-2-yl)(benz)imidazole ligand. Where it was found that these complexes exhibit strong absorption at 580-600 nm spectral range in dichloromethane. Our calculations based on time-dependent density functional theory (TD-DFT) predict that employing diamine-based ligands with varying conjugation positions or pyridocarbazoletype ligands, can significantly redshift the absorption bands into the NIR region up to 700 nm range. Furthermore, replacing 1-2 of the carbonyl groups with pyridines or bipyridines in these complexes extends the spectra from 500-700 nm up to 800-1100 nm and significantly enhances the optical activity of the lowest energy transitions, indicating promising avenues for eAicient emission. It was also found that this overall increase in conjugation on the molecules has increased the amount of mixing in singlet and triplet states in comparison to the 4 carbonyl cases. This indicated promising avenues for eAicient inter-system crossing for applications such as photodynamic therapy. Our results demonstrate a promising pathway toward the rational design of W(0) complexes with optical response in the NIR range, advancing the development of cost-eAective, earth-abundant NIR emitters for application in photocatalysis, bioimaging and photodynamic therapy.