Ultrafast Excited-State Processes in Re(I) Carbonyl-Diimine Complexes: From Excitation to Photochemistry

Rhenium(I) carbonyl-diimines are chemically robust and synthetically flexible photo- and redox active compounds that can be incorporated into supramolecular systems, polymers or biomolecules. They can be used as efficient and fast photosensitizers. In this chapter, we will follow excited-state evolution of ReI complexes from the instant of photon absorption through intersystem crossing, relaxation of "hot" triplet states, to their decay either to the ground state or to photoproducts. Out of many decay pathways, we concentrate on nonradiative decay following the energy gap law, excited-state electron- and energy transfer and ligand isomerization. Characterization of the lowest excited state by ultrafast IR spectroscopy and DFT calculations are discussed in detail. It is shown that excited-state properties are much influenced by mixing of Re(CO)3→diimine, L→diimine CT and intraligand ππ* excitations.