Theoretical study of the effects of different substituents of tetrathiafulvalene derivatives on charge transport

Density functional theory calculations were carried out to investigate the charge transfer of four tetrathiafulvalene derivatives. Perfluorination of dibenzo-tetrathiafulvalene (DB-TTF) increased the reorganization energy and was considered disadvantageous for the charge-transport process. Fluorination lowered the frontier orbitals of the compound, favoring electron-rather than hole-transport due to the low injection barrier. While intra-ring substitution of carbons of benzene with N atoms did not increase the reorganization energy, it enforced thermodynamic stability and decreased the charge injection barrier due to lowering the frontier orbital. Calculation results also showed that introduction of NH2 to DB-TTF can change the crystal structure and charge mobility, thus providing a method with which to promote E >-stacked structures. Calculation of charge transfer integrals using site energy correction methods was found to be more suitable for perfluorinated DB-TTF because it exhibits remarkable polarization effects.