Important role of molecular packing and intermolecular interactions in two polymorphs of (Z)-2-phenyl-3-(4-(pyridin-2-yl)phenyl)acrylonitrile. Preparation, structures, and optical properties

Abstract The novel compound Z -2-phenyl-3-(4-(pyridin-2-yl)phenyl)acrylonitrile ( PPyPAN ) was synthesized from the condensation reaction between phenylacetonitrile and 4-(pyridin-2-yl)benzaldehyde. This compound crystallizes in two forms: polymorph I (triclinic, P  − 1, Z′  = 2) and polymorph II (orthorhombic, Pbc 2 1 , Z′  = 2). The molecular structures and optical properties of the two polymorphs have been characterized via 1 H NMR, EI, FTIR, UV–Vis spectroscopy, DSC, single-crystal and XRPD. The molecular structure, packing properties, and intermolecular interactions were examined for both polymorphs of PPyPAN in order to interpret the emission properties. A subtle change in the molecular conformation (e.g., a rotation around single C C bonds) found for both polymorph plays an important role in their solid-state properties. The structure and optical properties of the new structures were well characterized and showed unique features for both polymorphic phases. For phase I , we observed an excitation spectrum with an λ ex at 325–346 nm, which is the maximum excitation or absorption wavelength for the lowest S o  →  S 1 transition, which is characteristic to the π–π * transition, and an emission spectrum with an λ em max at 454 nm. For phase II , the excitation spectrum showed an λ ex max at 325 nm, whereas the λ em max showed a red-shift to 492 nm.