Vibronic interactions and charge transfer in negatively charged chloroacenes

The vibronic interactions and single charge transfer through chloroacenes such as C6Cl6 (1cl), C10Cl8 (2cl), C14Cl10 (3cl), and C18Cl12 (4cl), and iodoacenes such as C6I6 (1i), C10I8 (2i), and C14I10 (3i) are discussed. The reorganization energies between the neutral molecules and the corresponding monoanions are estimated to be 0.344, 0.078, 0.060, and 0.047 eV for 1cl, 2cl, 3cl, and 4cl, respectively, and thus the reorganization energies decrease with an increase in molecular size in chloroacenes. This result implies that the smaller the molecular size of chloroacenes is, the larger overlap integral between the lowest unoccupied molecular orbitals (LUMO) of two neighboring molecules is needed for the molecule to become good conductor. On the other hand, the reorganization energies are estimated to be 0.138, 0.139, and 0.135 eV for 1i, 2i, and 3i, respectively. Therefore, the reorganization energies hardly change with an increase in molecular size in negatively charged iodoacenes. The C-C stretching modes around 1200-1600 cm−1 play an essential role in the vibronic interactions in the monoanions of chloroacenes, while the low frequency modes as well as the high frequency modes play an essential role in the vibronic interactions in the monoanions of iodoacenes. By comparing these calculated results for chloroacenes and iodoacenes with those for acenes and fluoroacenes, we investigate how the halogen substitutions are closely related to the characteristics of these physical values.