Theoretical Investigation of the Interactions Between the π-Systems of Molecular Organic Semiconductors and an Analysis of the Contributions of Repulsion and Electrostatics

A concept for the interactions between pi-systems is necessary to understand a number of phenomena in modern material sciences such as supramolecular properties and self-assembly. In the present article, we investigate the intermolecular interaction energies between organic semiconductors with extended pi-systems using SAPT (symmetry-adapted perturbation theory), LMO-EDA (localized molecular orbital energy decomposition analysis), DFT-D (density functional theory including dispersion corrections), and force-field approaches. Both apolar organic molecules such as acenes and highly polarized pi-systems of merocyanines and squaraines were used to probe the influence of electrostatics on the shape of the potential energy surfaces (PES) governing the geometric structures of aggregates. Our results reveal that the shapes of the PESs result from variations in the short-range, highly specific repulsion forces even for highly polar molecules. Using distributed quadrupoles, we show that it is nevertheless possible to mimic the intermolecular potentials with electrostatics. This is also possible with van-der-Waals potentials and a simple overlap-based force-field ansatz based on the overlap between p-orbitals. (C) 2016 Wiley Periodicals, Inc.