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

Pierre Frangville,Franck Meyer,Shiv Kumar,Kristof Van Hecke,Michel Gelbcke

doi:10.3390/molecules26247586

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.

Highlights

Stimuli responsive materials are fascinating compounds with the ability to translate a stimulus into a change of physical/chemical properties at the nano/macro-scale [1]
The preparation of halogen bonded azobenzenes was performed through a multistep synthesis (Scheme 1)
We have reported the synthesis of new azobenzene derivatives bearing halogen bond donor groups

Summary

Introduction

Stimuli responsive materials are fascinating compounds with the ability to translate a stimulus into a change of physical/chemical properties at the nano/macro-scale [1]. In the arena of smart systems, photo-responsive materials have a photo switching ability in a reversible or irreversible fashion that consists in chemical bond breaking/formation or a conformational change upon irradiation [11]. Among these switchable compounds, azobenzenes represent a very appealing class of molecules that can reversibly isomerize from trans to cis form and vice versa [12]. Structural modifications of the azobenzene core allow for a fine tuning/shifting of absorbance in the red region and even the near-infrared, whereas shorter wavelength UV radiation is generally used to induce the isomerization [14,15]

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Results

Conclusion