Charge transfer excitation of organometallic compounds - Spectroscopy and photochemistry

Excited state properties of organometallic compounds have been studied for many years. Owing to strong covalent bonding, molecular orbitals of organometallics are frequently delocalized. Accordingly, the usual classification, of electronic transitions in coordination compounds (e.g. metal-centered and charge transfer) may not always be appropriate. Nevertheless, in suitable cases various important organic ligands can function as CT donors (e.g. cyclopentadienyl anions, allyl anions, carbenes) and CT acceptors (e.g. acetylenes, carbenes, arenes, cyclohexadienyl cations, cycloheptatrienyl cations). Accordingly, organometallic complexes with these ligands are frequently characterized by CT absorptions. CT excitation can lead to an emission or photoreaction. This behavior is illustrated by selected examples which have been recently studied in our laboratory. (C) 2004 Elsevier B.V. All rights reserved.