Stimuli Responsive Materials Supported by Orthogonal Hydrogen and Halogen Bonding or I···Alkene Interaction

Abstract

Smart materials represent an elegant class of (macro)-molecules endowed with the ability to react to chemical/physical changes in the environment. Herein, we prepared new photo responsive azobenzenes possessing halogen bond donor groups. The X-ray structures of two molecules highlight supramolecular organizations governed by unusual noncovalent bonds. In azo dye I-azo-NO2, the nitro group is engaged in orthogonal H···O···I halogen and hydrogen bonding, linking the units in parallel undulating chains. As far as compound I-azo-NH-MMA is concerned, a non-centrosymmetric pattern is formed due to a very rare I···π interaction involving the alkene group supplemented by hydrogen bonds. The Cambridge Structural Database contains only four structures showing the same I···CH2=C contact. For all compounds, an 19F NMR spectroscopic analysis confirms the formation of halogen bonds in solution through a recognition process with chloride anion, and the reversible photo-responsiveness is demonstrated upon exposing a solution to UV light irradiation. Finally, the intermediate I-azo-NH2 also shows a pronounced color change due to pH variation. These azobenzenes are thereby attractive building blocks to design future multi-stimuli responsive materials for highly functional devices.

Recent Developments in Stimuli Responsive Smart Materials and Applications: An Overview

“…These materials include functionalized nanoparticles injected into the fiber matrix as well as unique or modified polymers that are employed in the creation of smart filaments, yarns, and textiles. Because of the variety of capabilities that a fabric substrate is capable of acquiring and the ways in which it may interact with its wearer, "smart textiles" have emerged as a material category that is both significant and innovative in the textile industry [36,37]. Due to the contemporary significance of the topic, the purpose of this review is to present, in a condensed form, the basic aspects of a smart textile, as well as its categories, various applications, and highlight the primary materials used in the preparation of intelligent textiles.…”