Charge Transfer and Delocalization in Conjugated (Ferrocenylethynyl)oligothiophene Complexes

Abstract

A series of conjugated mono(ferrocenylethynyl)oligothiophene and bis(ferrocenylethynyl)oligothiophene complexes have been prepared. The cyclic voltammograms of the complexes all contain a reversible ferrocene oxidation wave and an irreversible oligothiophene-based wave. The potential difference between the two waves (Δ E ) varies from 0.38 to 1.12 V, depending on the length and substitution of the oligothiophene group. Several of the mono(ferrocenylethynyl)oligothiophene complexes couple when oxidized, resulting in the deposition of a redox-active film on the electrode surface. In solution, electrochemical oxidation of the Fe II centers yields the corresponding monocations and dications, which exhibit oligothiophene-to-Fe III charge-transfer transitions in the near-IR region. The band maxima of these low-energy transitions correlate linearly with Δ E, while the oscillator strengths show a linear correlation with negative slope with Δ E . The complexes with similar charge-transfer transition dipole lengths show an increase in the extent of charge delocalization with smaller Δ E . Comparisons between complexes with different length oligothiophene ligands show that a reduction in Δ E results either in greater delocalization of charge or in charge being delocalized further along the rigid oligothiophene ligand. These results have important implications in understanding charge delocalization in metal-containing polymers.