Mechanism of Förster-type hopping of charge transfer and excitation energy transfer along blocked oligothiophenes by Si-atoms

Abstract

The ground and excited-state properties of oligothiophenes connected by Si-atoms have been studied theoretically, based on recent experimental reports [M. Fujitsuka, D.W. Cho, J. Ohshita, A. Kunai, T. Majima, J. Phys. Chem. C 111 (2007) 1993]. Herein, we have employed a density-functional theory (DFT) approach toward examining the influence of the number of oligothiophenes on molecular ground-state properties, focusing on the density of state and the density distribution on the subunit of the oligothiophenes. Furthermore, we have investigated several excited-state properties of these oligothiophene. We discuss absorption with transition densities, which reveal the orientations and strengths of transition dipole moments, charge difference densities, which allow for the study of transition dipole moments and charge transfer in the absorption processes, and transition density matrices, which provide information about the electron–hole coherence and excitation delocalization. All of these properties were studied by employing time-dependent density functional theory (TD-DFT). Our theoretical results indicate that there are not only localized excited states, but also inter-branched charge transfer excited states in absorption for block copolymers of the oligothiophenes. In all, the theoretical analyses provide insight into the ground- and excited-state properties of the polymers, notably on the hopping mechanism of charge transfer in blocked oligothiophenes by Si atoms.