Characterization of the Low-Energy Electronic Excited States of Benzoyl-Substituted Ferrocenes

Resonance Raman spectroscopy has been employed to probe the excited-state distortions associated with the low-energy electronic transition of benzoylferrocene and 1,1ʹ-dibenzoylferrocene. Resonance intensity enhancement of in-plane ligand modes, in general, and the carbonyl stretching mode, in particular, supports the proposal that the excited state populated by this transition contains appreciable metal-to-ligand charge transfer character. The redistribution of charge that occurs upon populating this state weakens the metal-ring bonding and facilitates the loss of a benzoylcyclopentadienide anion. This photochemical reaction has been investigated by an on-line electrospray ionization mass spectrometry technique that allows direct detection of primary and secondary products with solution lifetimes down to the millisecond range.