Photoresponsive Halogen-Bonded Complexes of 1,3,5-Trifluoro-2,4,6-triiodobenzene and Alkoxyazopyridine Derivatives Based on Py-N<middle dot><middle dot><middle dot>I Interactions: Synthesis, Structural, and Theoretical Insights

A series of (E)-4-((4-alkoxyphenyl)diazenyl)pyridine (AZ-n ) derivatives were synthesized with varying alkoxy spacers (n = 8, 9, and 10), and their halogen-bonded complexes were obtained with 1,3,5-trifluoro-2,4,6-triiodobenzene in different stoichiometric ratios, which were further characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), single-crystal X-ray diffraction (SC-XRD), and powder X-ray diffraction (P-XRD) techniques. The structural analysis revealed the presence of Py-N<middle dot><middle dot><middle dot>I halogen bond (XB) interactions in the complexes, resulting in a bent-shaped architecture rather than a star-shaped one. Hirshfeld surface analysis revealed the contribution of XB along different intermolecular interactions in the crystal packing. Computational analyses such as noncovalent index (NCI), quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), and natural bond orbital (NBO) were carried out to understand the nature, strength, and electronic characteristics of XBs in these complexes. Further, these XB complexes show excellent photoresponsive behavior upon UV illumination, introducing a new range of supramolecular photoresponsive materials self-assembled by halogen bonding, thereby broadening the scope of potential applications within their respective systems.