Redox and Optical Properties of Conjugated Ferrocene Oligomers

Internuclear electronic interactions in conjugated ferrocene oligomers display unique redox and optical properties. I describe here recent research on the dependence of such properties on the number of ferrocene nuclei and on the structure of conjugated spacers. The neighboring-site interaction model explains the redox properties of oligo(ferrocene-1,1′-diyl)s. The infrared (IR) spectra of carbonyl complex-bound biferrocene and terferrocene enlighten the electronic structure in the mixed-valence states. Energy shifts of intervalence transfer (IT) in the mixed-valence states of oligo(ferrocene-1,1′-diyl)s resulting from changes in the oxidation state are rationalized by taking into account the change in neighboring-site combination by photo-electron transfer, which delivers extra energy due to the strain in internuclear distance. Oligo- and poly-(ferrocene-1,1′-diyl)s oxidized partially by tetracycanoethylene (TCNE) exhibit near-IR photoconductivity. Conjugated spacer groups between ferrocene nuclei involving metal complex moieties affect the redox properties of ferrocene dimers significantly. The azo group acts as a distinctive spacer of which conjugation ability is changeable photochemically.