posted on 2006-03-30, 00:00authored bySilvia Fratiloiu, Ferdinand C. Grozema, Yoshiko Koizumi, Shu Seki, Akinori Saeki, Seiichi Tagawa, Stephen P. Dudek, Laurens D. A. Siebbeles
The electronic structure and optical properties of charged oligofluorenes were studied experimentally and
theoretically. Measurements of the optical absorption spectra of charged oligofluorenes in dilute solutions
have been performed by using the pulse radiolysis technique. In addition, optical absorption spectra of radical
cations and anions in a solid matrix were measured after γ-irradiation at 77 K. The optical absorption spectra
were measured in the range of 440−2100 nm (0.6−2.8 eV) and compared with results from time-dependent
density functional theory (TDDFT) calculations. The calculated charge induced deformations and charge
distribution do not indicate the occurrence of polaronic effects. The potential energy profiles for rotation
around the inter-unit bond show that oligofluorenes are nonplanar in their neutral state, while they tend to
more planar structures in their charged state. The optical absorption spectra of charged oligofluorenes are
dependent on the angle between neighboring units. TDDFT absorption energies shift to lower values with
increasing chain length, which suggests that the charge delocalizes along the oligomer chain.