Charge-transfer excited states of π- and 4f-orbitals for trivalent Eu complexes

Abstract

There are increasing reports on the charge-transfer (CT) excited states of the ligand (π)- and 4f-orbitals of lanthanide complexes, where the latter are shielded by the filled 5s² and 5p⁶ orbitals. To date, the factors that influence CT through the 4f-orbitals remain unknown. Therefore, since this research area is relatively new, we believe that the study of photo-excited π-4f-orbital CT will open up a new field of research in photochemistry based on metal complexes. In this review, we highlight the historical views and research progress in the π-4f-orbital CT excited states of lanthanide complexes.