| Abstract
| - Electron−phonon interactions in the monoanions of polyacetylenes such as C2H4 (2tpa), C4H6 (4tpa), C6H8(6tpa), and C8H10 (8tpa) are studied and compared with those in the monoanions of polyacenes. The C−Cstretching Ag modes around 1500 cm-1 the most strongly couple to the lowest unoccupied molecular orbitals(LUMO) in polyacetylenes. The estimated total electron−phonon coupling constants for the monoanions(lLUMO) are 0.579, 0.555, 0.463, and 0.401 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. The lLUMO valuesfor polyacetylenes are much larger than those for polyacenes. Furthermore, the lLUMO value for polyacetylenewith C2h geometry is estimated to be 0.254 eV, and is larger than that (0.024 eV) for polyacene with D2hgeometry. The phase patterns difference between the LUMO of polyacenes localized on the edge part ofcarbon atoms, and the delocalized LUMO of polyacetylenes is the main reason for the calculated results. Thesingle charge transfer through the molecule in polyacetylenes are also discussed. The reorganization energiesbetween the neutral molecule and the corresponding monoanion are estimated to be 0.164, 0.144, 0.125, and0.113 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. Such reorganization energy decreases with an increasein molecular size. The conditions under which the attractive electron−electron interactions are realized in themonoanions of polyacetylenes and polyacenes are discussed. In terms of the electron−phonon interactionsand the reorganization energies, the relationships between the normal and possible superconducting states arebriefly discussed. We find that the monoanions with smaller molecular size cannot easily become goodconductors, however, the conditions under which the interactions between two electrons are attractive aremore easily realized in the monoanions with smaller molecular size than in the monoanions with largermolecular size.
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