Quantum-chemistry-aided ligand engineering for potential molecular switches: changing barriers to tune excited state lifetimes

Abstract

Substitution of terpyridine at the 4′ position with electron withdrawing and donating groups is used to tune the quintet lifetime of its iron(II) complex. DFT calculations suggest that the energy barrier between the quintet and singlet states can be altered significantly upon substitution, inducing a large variation of the lifetime of the photoexcited quintet state. This prediction was experimentally verified by transient optical absorption spectroscopy and good agreement with the trend expected from the calculations was found. This demonstrates that the potential energy landscape can indeed be rationally tailored by relevant modifications based on DFT predictions. This result should pave the way to advancing efficient theory-based ligand engineering of functional molecules to a wide range of applications.