The effect of the supramolecular network of (Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-2-yl)-acrylonitrile on the fluorescence behavior of a single crystal: experimental and theoretical studies

Abstract

The molecular structure and molecular interactions of an α,β-unsaturated nitrile, such as the interaction between adjacent molecules of (Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-2-yl)-acrylonitrile (Z-DPPyACN) throughout the 4-diphenylamino moiety with the phenyl and pyridyl rings, play an important role in the self-assembly behaviors and optical properties of its powder and single-crystal forms. The crystal packing exhibits multiple C–H⋯π and CH⋯HC edge-to-face interactions that contribute to the supramolecular network between adjacent molecules. The resulting molecular structure resembles a pinwheel which exhibits a strong emission intensity at three different wavelengths. The crystal belongs to the monoclinic space group P2₁/n, with dimensions a = 12.9551(2), b = 11.29300(15), c = 14.6992(3) Å, β = 115.648(2)° and Z = 4. The single-crystal compound shows three emission maxima at 533, 569, and 607 nm, whereas the powder and the molecules in an aggregated state show maximum emission intensities that are dependent on the nature of the solvent. The Z-DPPyACN dye's optical properties show a Stokes shift caused by the reorganization of the molecule in the excited state, as effected by the solvent polarity. This indicates a large change in the dipole moment of dye molecules upon excitation due to an intramolecular charge transfer interaction. From a theoretical point of view, the molecular geometry, electronic structure, and excitation energies are reported using density functional theory and compared with the experimentally determined one photon absorption and emission spectra.