High charge delocalization and conjugation in oligofuran molecular wires.
The extent of charge delocalization and of conjugation in oligofurans and oligothiophenes was studied by using mixed valence systems comprising oligofurans and oligothiophenes capped at both ends by ferrocenyl redox units. Using electrochemical, spectral, and computational tools, we find strong charge delocalization in ferrocene-capped oligofurans which was stronger than in the corresponding oligothiophene systems. Spectroscopic studies suggest that the electronic coupling integral (H(ab)) is roughly 30-50 % greater for oligofuran-bridged systems, indicating better energy matching between ferrocene units and oligofurans. The distance decay constant (damping factor), β, is similar for oligofurans (0.066 A(-1)) and oligothiophenes (0.070 A(-1)), which suggests a similar extent of delocalization in the bridge, despite the higher HOMO-LUMO gap in oligofurans. Computational studies indicate a slightly larger extent of delocalization in furan-bridged systems compared with thiophene-bridged systems, which is consistent with oligofurans being significantly more rigid and less aromatic than oligothiophenes. High charge delocalization in oligofurans, combined with the previously reported strong fluorescence, high mobility, and high rigidity of oligofuran-based materials makes them attractive candidates for organic electronic applications.