Correlation between structural and optical properties of π-conjugated acrylonitrile derivatives: Insights from X-ray, energy frameworks, TD-DFT and charge density analysis

Abstract The 2/3/4-pyridyl substituents incorporated into a π-conjugated acrylonitrile system have been synthesized and X-ray structure analysis of two of the isomers (Z)-3-(4-pyridin-2yl)phenyl-2-(pyridine-3yl)acrylonitrile (II) and (Z)-3-(4-pyridin-2yl)phenyl-2-(pyridine-4yl)acrylonitrile (III) are reported. The molecular structure and UV–Vis absorption properties of (Z)-3-(4-pyridin-2yl)phenyl-2-(pyridine-2yl)acrylonitrile (I) has been explored by density functional theory (DFT) with the M06–2X/cc-pVTZ level of theory. The molecular structure analysis reveals that the isomer in para position shows a conformation more planar than the isomer in meta position. The electrostatic potential surface maps of these isomers highlight the similarities and differences in the most positive and the most negative electrostatic potentials and also reveal the effect of crystal packing. Intermolecular interactions present in the crystal structures of isomers II and III have been qualitatively characterized using Hirshfeld surface analysis and 2D-fingerprint plots. Differences in the contribution of intermolecular H⋯C and C⋯C interactions were found between isomers. The theoretical charge density analysis has been performed for selected molecular pairs identified from the crystal structures. The results revealed that the C–H⋯N and C–H⋯C(π) interactions showed H-bond character. The Laplacian of the electron density, the ratio between potential and kinetic energy densities and the total energy density for intermolecular H⋯H interactions suggest that these interactions were closed-shell in nature. Further, experimental and theoretical UV–Vis absorption properties for isomers I-III are compared and agreed well.