Abstract
The discovery of photoswitchable azobenzene-systems that undergo trans-to-cis photoisomerisation was a milestone in supramolecular chemistry. Such photoswitches have possible applications in data storage, stimuli responsive delivery systems, and molecular machines due to fast and selective switching. However, the light induced cis isomer of azobenzene is rather unstable and reverts thermally and photochemically to the thermodynamically stable trans configuration. We report, for the first time, controlled photoswitching of an azo-naphthalenediimide (azo-NDI) which can be achieved upon binding of fluoride ions through anion-π interaction. This NDI-F–NDI “sandwich” stabilises the cis configuration through the generation of an NDI•− radical anion, and a dianionic, NDI2− species that becomes unusually stable in the cis form. The sandwiched cis form reverts to the trans form only upon decomplexation of F−. A model pollutant was successfully degraded using the photogenerated NDI-F–NDI sandwich. This opens a wide range of applications in molecular and supramolecular nanotechnology.
Highlights
The discovery of photoswitchable azobenzene-systems that undergo trans-to-cis photoisomerisation was a milestone in supramolecular chemistry
Inspired by the reports of anion-π interactions of the NDI units[38], we report an unprecedented example of an NDI based receptor appended to an azobenzene photoswitch that undergoes trans to cis photoisomerization, where the thermodynamically unstable cis isomer has been conferred high stability in the presence of F− through the formation of stable anionic species of NDIs i.e. NDI− and NDI2− that are stabilized by anion-π interactions
In the presence of excess F− it forms doubly charged azo-NDI2− anion which is Electron paramagnetic resonance (EPR) silent owing to its closed shell electronic structure
Summary
The discovery of photoswitchable azobenzene-systems that undergo trans-to-cis photoisomerisation was a milestone in supramolecular chemistry. Among the molecules used for switching, diarylethenes[11], spiropyrans[12,13] and azobenzenes[14,15,16,17,18] are well-known In most of these reported cases the cis-to-trans switching of azobenzene photoisomers in both directions occur reversible in multiple cycles with no chemical degradation, making the azobenzene based scaffold a highly potential candidate for an effective molecular switch with convertible isomers[19,20]. There have been effective approaches where the azobenzene is incorporated into macrocyclic scaffolds, which can have a dramatic influence on the switching mechanism due to the stabilisation of cis isomer caused by ring strain[22] Such macrocyclic arrangements are of great interest to the field of molecular computing as they were found to self-assemble on surfaces[23] or self-organise into supramolecular channels[24]. Inspired by the reports of anion-π interactions of the NDI units[38], we report an unprecedented example of an NDI based receptor appended to an azobenzene photoswitch that undergoes trans to cis photoisomerization, where the thermodynamically unstable cis isomer has been conferred high stability in the presence of F− through the formation of stable anionic species of NDIs i.e. NDI− and NDI2− that are stabilized by anion-π interactions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
