LAUSR

Abstract The optical properties on two polymorphic structures of (Z)-2-phenyl-3-(4-(pyridin-2-yl)- phenyl)acrylonitrile (PPyPAN) have been studied by the TD-DFT and QM/MM-ONIOM approaches. The quantitative analysis of intermolecular interactions in both polymorphs (polymorph-I and polymorph-II) was carried out by using PIXEL, quantum theory of atoms-in-molecules (QTAIM), and Hirshfeld surface (HS) analysis. The weak C–H⋯N, C–H···π, and π···π interactions are stabilized their crystal packings. Particularly, the weak C–H⋯N, and C–H···π interactions are dominated in polymorph-I and the π···π interactions in polymorph-II. The lattice energy of polymorph-I is 1.6 kcal mol−1 higher than the polymorph-II, but the % EDisp contributions are higher in polymorph-II. This increase is due to the presence of π···π interactions. The H⋯C/C⋯H contacts are dominated in polymorph-I (47.7% in molecule A and 46.1% in molecule B). Whereas, the H⋯H contacts are dominated in polymorph-II (41.9% in molecule A and 41.5% in molecule B). The calculated absorption (λmax) and emission (λem) wavelengths for two molecules (molecule A and molecule B) in the asymmetric units of both polymorphs are in good agreement with their experimental results. The computed λmax value is of 416 nm (2.98 eV) for polymorph-I and 440 nm (2.82 eV) for polymorph-II. The natural bond orbitals (NBO) analysis suggests that the whole backbone of the PPyPAN molecule participates in the intermolecular charge transfer process in polymorph-II whereas the pyridine ring (ring 1) is not involved in polymorph-I. Also, the equilibrium atomic positions and unit cell parameters at the ground state environment are calculated with the aid of CRYSTAL09 and these values are in good agreement with the experimental results.