Toward the Computational Design or Iron-Based Chromophores

October 7, 2016

Elena Jakubikova

Photoactive transition metal complexes anchored to semiconductor surfaces play an important role as chromophores in artificial systems for solar energy conversion, such as dye-sensitized solar cells (DSSCs). Successful chromophores in DSSCs absorb light in the visible region of the solar spectrum, possess the ability to achieve long-lived charge-separated states, and undergo interfacial electron transfer (IET) into the semiconductor. Fe(II)-polypyridines have recently gained attention as potential candidates for dye sensitizers due to the low cost and high abundance of iron. Visible light excitation of Fe(II)-polypyridines results in the population of photoactive metal-to-ligand charge transfer states (MLCT), that are capable of undergoing IET into a semiconductor. The IET in the Fe(II)-polypyridine-TiO2 assemblies, however, competes with the ultrafast intersystem crossing (ISC) into the manifold of non-photoactive high-spin metal-centered (MC) states of the Fe(II) photosensitizer. We employ density functional theory (DFT), time-dependent DFT, and quantum dynamics simulations to investigate how various structural features of the polypyridine ligands and dye-TiO2 semiconductor interface influence the ISC and IET events. Our goal is to obtain a deeper understanding of the structure-property relationships in these systems, so that we can formulate a set of guidelines for rational design of more efficient Fe-based chromophores.