Stack bonding in pentacene and its derivatives

Abstract

Understanding the nature of π-stacking interactions is important to molecular recognition, self-assembly, and organic semiconductors. The stack bonding order (SBO) model of π-stacking has shown that the conformations of dimers occur when the combinations of monomer MOs are overall stack bonding in character. DFT calculations show that minima found on the potential energy surface for the π-stacked dimers of pentacene and perfluoropentacene occur when the dimer MOs are constructed from combinations of monomer MOs with an allowed SBO. An ex-amination of the MOs of π-stacked dimers extracted from X-ray structures of alkynyl derivatives like TIPS-pentacene pack at one or more of the minima expected to show similar MO patterns. The -stacking variability within these materials can be attributed to a balance between the minima allowed by SBO theory and steric effects within the lattice. The offset orientation of the pentacene cores observed in packing of these materials is attributed to the increased overlap of monomer lobes in the dimer and a reduction in two-orbital-four-electron repulsions. Charge mobility estimated from the frontier MOs of the dimer are related to the MO structure that favors PD conformations.