Structural, Thermal, and Computational Investigation into Halogen-Bonded Photoresponsive Alkoxy Azo Benzonitrile Derivatives

The versatility of halogen bonds (XBs) has made them an attractive tool for the design and development of photoresponsive materials. In this work, we have synthesized XB complexes of the alkoxy azo benzonitrile derivative with 1,4-diiodotetrafluorobenzene. The formation of these complexes was confirmed by FTIR spectroscopy and powder X-ray diffraction analysis, while their structural details were further elucidated through single crystal X-ray diffraction studies. To gain deeper insights into the nature of the interactions, computational analyses including molecular electrostatic potential mapping, noncovalent interactions index analysis, quantum theory of atoms in molecules, and natural bond orbital analysis were performed. These studies revealed the weak but significant nature of the XBs, providing both qualitative and quantitative descriptions of these intermolecular interactions. The thermal behavior of the complexes was evaluated by thermogravimetric analysis, differential scanning calorimetry, and hot-stage polarized optical microscopy. The results indicated low thermal stability and the absence of liquid crystalline phases. Interestingly, despite these limitations, the complexes exhibited reversible photoresponsive behavior upon irradiation with suitable wavelengths of light, underscoring their potential for use in light-driven molecular switches and smart materials.