Co-crystals of polynuclear aromatic hydrocarbons and 9H-carbazole with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone acceptor: Varieties in crystal packing, Hirshfeld surface analysis and quantum-chemical studies

Abstract

Co-crystals formed by polynuclear aromatic hydrocarbons (PAH) chrysene, benz(a)anthracene, triphenylene(9,10-benzophenanthrene), benzo(a)pyrene, dibenz[a,c]anthracene, and 9H-carbazole as π-electron-donor (D) molecules, with π-electron acceptor, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) were synthesized, and their crystal structures were determined using single-crystal X-ray diffraction analysis. All co-crystals exhibit 1:1 donor / acceptor ratio and adopt mixed-stacking motifs. The donor(D)-acceptor (DDQ) π-π interactions in stacks are complemented by different sets of D…D, D…DDQ and DDQ…DDQ intermolecular interactions between stacks whose diversity originates from different degree of D/DDQ mismatch and manifests in dissimilar crystal packing motifs. The parallel face-to-face stacking was registered in chrysene-DDQ, while benz(a)anthracene-DDQ reveals brickwork crystal packing with significant parallel slippage. The rest four co-crystals show fairly different herringbone-type crystal packing with rearrangement of intermolecular interactions. The distribution of intermolecular contacts and impact of π-π interactions were evaluated through Hirshfeld surface analysis. Molecular orbital energies as well as bandgaps were calculated using DFT. Degree of charge-transfer was estimated based on bond length distribution in the acceptor molecule for each of the co-crystals.