Electronic properties of the charge carriers on oligofluorene backbone

The transient absorption of radical anions and cations of 9,9′-di-n-hexyl-oligofluorene was measured using pulse radiolysis and low-temperature γ-radiolysis techniques. The infrared absorption maxima of both radical anions and cations exhibit red-shift continuously upon elongation of the chain length. The absorption bands are blue-shifted by 0.04-0.07 eV with increasing the temperature from 80 to 106 K. The extinction coefficients were determined by scavenging technique, demonstrating an increase with the elongation of the chain length. The optimized geometry of fluorene trimers, calculated using density functional theory, shows that the oligofluorene molecules are more planar in its charged state than in its neutral state.