title: Electronic structure and optical properties of dianionic and dicationic pi-dimers.
abstract: The absorption spectra of dianionic tetrocyanoethylene and dicationic tetrathiafulvalene dimers have been studied theoretically with the time-dependent density functional theory and the recently proposed Coulomb-attenuated model. The nature of the excited states was further explored by means of the two-dimensional (2D) site (transition density matrix) and three-dimensional (3D) cube (transition density and charge difference density) representations. By use of the 3D transition density and charge difference density, we visualized the orientation of transition dipole moment and also explained charge-transfer characteristics occurring in the dianionic/dicationic pi-dimers system. It is found that for the dianionic/dicationic pi-dimers system there exist two kinds of charge-transfer patterns for the mainly excited states, the intermolecular charge transfer and the mixture of intramolecular charge transfer coupled with intermolecular charge transfer. Meanwhile, the coupling effect of excitation and the oscillation of electron-hole pairs between the monomers have been revealed with 2D site representation of transition density matrix, which also indicates the electron-hole coherence upon photon excitation.
authors.affiliation: School of Physics and Optoelectronic Technology, and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, People's Republic of China.
authors.forename: Yuanzuo
authors.initials: Y
authors.lastname: Li
authors.forename: Huixing
authors.initials: H
authors.lastname: Li
authors.forename: Xiuming
authors.initials: X
authors.lastname: Zhao
authors.forename: Maodu
authors.initials: M
authors.lastname: Chen
mesh_terms: D000042:Absorption; D019281:Dimerization; D004579:Electron Transport; D004583:Electrons; D005030:Ethylenes / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D055620:Optical Phenomena; D011789:Quantum Theory
chemical_list: D005030:Ethylenes; C036216:ethylene