Suppression of the Sigma-Transmission by Destructive Quantum Interference in Pi-Conjugated Molecules

Molecular dielectric materials require ostensibly conflicting requirements of high polarizability and low conductivity. As previous efforts towards molecular insulators focused on saturated molecules, where the polarizability will be generally less than conjugated molecules, it remains an open question whether electron transport can be comprehensively suppressed in conjugated systems. Here, we demonstrate that the s-transmission in conjugated oligophenyl

systems can be suppressed by destructive sigma-interference. Using density functional theory, we study the Landauer transmission and ballistic current density, which allow us to determine how the transmission is affected by structural changes in the molecule. In para-linked phenyl rings, the sigma- transmission can be suppressed by changing the remaining hydrogens to methyl substituents due to the inherent gauche-like structure of a benzene ring. When two neighboring phenyl rings are orthogonal to each other, the transmission through both pi- and sigma-systems can be effectively suppressed, making methyl-substituted oligophenyls promising candidates for conjugated insulators.