CAS: Functionalization of Earth-Abundant, Molecular Group 4 Photosensitizers for Photochemical Applications

WIth support from the Chemical Structure, Dynamics & Mechanisms-B (CSDM-B) Program of the Chemistry Division and the Established Program to Stimulate Competitive Research (EPSCoR), Carsten Milsmann of the Department of Chemistry at West Virginia University is developing new synthetic routes to molecular transition metal photosensitizers based on earth abundant group 4 elements that can be utilized in photochemical applications. The goal of this research is to provide cheap and readily available light-absorbing molecules with characteristics required for solar fuels production, photocatalysis in polar solutions, and the construction of photovoltaic devices (e.g., dye-sensitized solar cells). Fundamental insights gained from the proposed work will broaden the scope of available photosensitizers and allow the targeted design of light-harvesting molecules in a more sustainable way. The proposed studies combine elements of synthetic organic and inorganic chemistry with detailed photophysical investigations, allowing for training and education of graduate and undergraduate students with diverse interests for their future careers as scientists. Early transition metal photosensitizers with long-lived ligand-to-metal charge transfer (LMCT) excited states are an emerging class of inorganic chromophores that have found application in photocatalysis, photon upconversion, and biological sensing. The proposed research includes the use of postsynthetic modification of existing molecular architectures to (i) improve performance critical parameters such as stability and solubility in polar solvents; (ii) incorporate anchoring groups for immobilization on metal oxide surfaces, thereby facilitating light-driven hole injection into p-type semiconductors; (iii) explore the influence of molecular symmetry on the optical properties of group 4 photosensitizers (e.g. intersystem crossing rates, lifetimes, and quantum yields) and provide asymmetric complexes to facilitate directional charge transfer upon visible-light excitation; and (iv) explore the chemical space for group 4 photosensitizer design and provide fundamental understanding of the underlying design principles for early transition metal chromophores. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.