Understanding Aggregate Structures of Organic Donor-Acceptor Systems by Partitioning Repulsive Interactions into Orbital-Orbital Contributions
Year: 2026
Type: preprint
Abstract: Molecular Orbital-Pair Contributions to the Exchange repulsion (MOPCE) are used to elucidate the orbital origin of repulsive interactions and to understand their role in determining the stacking arrangements of organic donor–acceptor (DA) complexes. We investigate three DA complexes with planar monomers, benzene–p-benzoquinone (BZ–pBQ), benzene–tetracyanoethylene (BZ–TCNE), and tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ), which prefer distinct stacking geometries. Symmetry-Adapted Perturbation Theory (SAPT) is employed to decompose the intermolecular interaction energy into electrostatic, induction, dispersion, and exchange repulsion contributions. MOPCE partitions the latter into a sum of orbital-orbital interactions, Exr(a, b), where a and b stand for the occupied orbitals of the interacting systems. Thus, MOPCE also permits to identify the π-π-, π-σ-, and σ-σ-contributions to the exchange repulsion energy. Its π-π-contribution is shown to play a decisive role for the intermolecular energy landscape of π-stacked DA complexes, despite the attractive contributions are dominated by dispersion and electrostatics. The energetically most favorable slip-stacked structure of the BZ–pBQ complex is traced back to oscillations of a MOPCE term with similarly shaped orbitals that have a node orthogonal to the shift direction. The face-to-face arrangements preferred by BZ–TCNE and TTF–TCNQ can be rationalized by reduced orbital overlap due to the nodal patterns of the π-orbitals. The non-negligible role of electrostatic interactions is discussed. The MOPCE approach is shown to be an intuitive orbital-based description of exchange repulsion which provides a valuable framework for understanding and predicting arrangements in stacked organic π-systems in terms of the wave-function nature of the underlying electronic structure.
Source: ChemRxiv
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7208719113