Color properties and non-covalent interactions in hydrated (Z)-4-(1-cyano-2-(2,4,5-trimethoxyphenyl)-vinyl)pyridin-1-ium chloride salt: Insights from experimental and theoretical studies

The optical charge-transfer (CT) property and the crystal structure of (Z)-4-(1-cyano-2-(2,4,5-trimethoxyphenyl)vinyl)pyridin-1-ium chloride monohydrate salt (I), which belongs to an acry-lonitrile family, was studied. The title salt, I, was characterized using different spectroscopy techniques and a single-crystal X-ray diffraction study combined with quantum chemical com-putations. The results showed that the color properties of I are determined by the CT, changes in bandgap, optical absorption, and various non-covalent interactions. The HOMO-LUMO energy gaps are 5.41 eV and 5.23 eV for the precursor and salt, respectively. It was demonstrated that pi-pi stacking interactions lead to the formation of intercalated dimers and donor-acceptor interactions assisted by hydrogen bonds; the dimers and interactions are different between the precursor and the salt. The cation moiety is mainly stabilized by N(1)+-H & sdot;& sdot;& sdot;Cl, and the anion is predominantly stabilized by strong O(1W)- HMIDLINE HORIZONTAL ELLIPSIS Cl- bonds as well as the hydrogen bonds with the MeO group O (2W)-HMIDLINE HORIZONTAL ELLIPSISO(1) and O(2W)-HMIDLINE HORIZONTAL ELLIPSISO(1W). The charge transfer between cation and anion moieties in the structure is established through NBO analysis.