End-substitution effect on the geometry and electronic structure of oligoheterocyclics

Abstract

The end-substitution effects on the geometric and electronic structures of oligoheterocyclics are systematically studied using the density functional theory. It is found that the influence of the end-substitution does not depend on the heteroatom. End-substitution plays a fine-tune effect on the geometry and the excitation state. While the influences on the conducting type (p-type or n-type) and the inter-chain charge carrier hoping channels are much different between the electron-donating –CH3 and electron–accepting –CN substitutions. Both molecular electrostatic potentials and charge carrier injection rates indicate that the –CH3/–CH3 substitution is beneficial to the p-type doping, while the –CN/–CN substitution is in favor of the n-type doping, which is in agreement with the experimental observations. The –CH3 substituted packing dimers exert similar intermolecular interactions to the unsubstituted ones. The –CN substituted packing dimers yield much stronger intermolecular interactions comparing to the –CH3 substituted ones. It could be anticipated that the –CN substitution would be helpful to the charge carrier hopings between chains and thereby enhance the conductivity.