Electronic and optical properties of conjugated group 8 metallocene derivatives

Ferrocene and ruthenocene have been incorporated into a range of conjugated systems. The interaction of these metallocene donor moieties with conjugated substituents is more complex than that of organic donors; both metal-based and ligand-based orbitals of the metallocene interact with the orbitals of the π-system. Here we review the rôle of these interactions in giving rise to a variety of interesting properties including non-linear optical activity in donor–acceptor systems, mixed-valence behaviour in bis(ferrocenyl) compounds, and structural distortions in polymethines.