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.

Halogen-Bonded Thiophene Derivatives Prepared by Solution and/or Mechanochemical Synthesis. Evidence of N···S Chalcogen Bonds in Homo- and Cocrystals

“…The shift in 19 F{ 1 H} NMR spectra of ThioI and ThioI/ TBACl (ratio 1:10; TBACl = n-tetrabutylammonium chloride) in CDCl 3 suggests the ability of ThioI to be engaged in I•••Cl − halogen bonding (Figure 8). 71 This observation broadens up the scope of ion-mediated self-assembly of neutral thiophenebased conductive π-conjugated polymers.…”