Electron-phonon interactions in the monoanions of fluoroacenes

Electron-phonon interactions in the monoanions of fluoroacenes such as C6F6 (1f), C10F8 (2f), C14F10 (3f), C18F12 (4f), and C22F14 (5f) are studied, and compared with those in the monoanions of acenes and deutero-acenes. The C-C stretching modes around 1500 cm-1 the most strongly couple to the lowest unoccupied molecular orbitals (LUMO) in fluoroacenes. The estimated total electron-phonon coupling constants (l(LUMO)) are 0.475, 0.473, 0.350, 0.273, and 0.215 eV for 1f, 2f, 3f, 4f, and 5f, respectively. The l(LUMO) values for fluoroacenes are much larger than those for acenes and deutero-acenes. Possible superconducting transition temperatures (T(c)s) for the monoanions of deutero-acenes and fluoroacenes are estimated to be larger than those for the monoanions of acenes. The transition temperature (T-c) value increases much more significantly by H-F substitution than by H-D substitution in acenes. The l(LUMO) and T-c values significantly decrease with an increase in molecular size from the monoanions of 1f to 5f. The logarithmically averaged phonon frequencies (omega(ln)) do not significantly change with an increase in molecular size in the monoanions of fluoroacenes. The larger displacements of carbon atoms in the vibronic active modes in fluoroacenes than those in deutero-acenes due to larger atomic mass of fluorine than that of deuterium, and the unchanged properties of the orbital patterns of the LUMO as a consequence of H-F and H-D substitution in acenes, are the main reasons why the l(LUMO) value increases much more significantly by H-F substitution than by H-D substitution, and the reason why the T-c value increases much more significantly by H-F substitution than by H-D substitution in acenes. That is, the detailed properties of vibronic active modes and the electronic structures in the LUMO as well as the molecular weights are closely related to the l(LUMO), omega(ln), and T-c values in the monoanions of fluoroacenes, deutero-acenes, and acenes. (C) 2003 American Institute of Physics.