Reversible 2D Supramolecular Organic Frameworks encompassing Viologen Cation Radicals and CB[8

Kanagaraj Madasamy,David Velayutham,Vellaiah Maruthiah Shanmugam,Murugavel Kathiresan

doi:10.1038/s41598-018-19739-7

Abstract

Reversible 2D supramolecular organic frameworks encompassing branched viologen architectures and cucurbit[8]uril (CB[8]) were constructed and investigated. UV-vis investigation clearly indicates the formation and intermolecular dimerization of monocation radicals and their encapsulation into the hydrophobic CB[8] cavity which is further complemented by EPR (electron paramagnetic resonance) spectroscopy. Particle size measurements by dynamic light scattering method showed particle sizes in the range of several µm indicating larger aggregates. Zeta potential measurements suggested the instability of these particles and their tendency to form aggregates. TEM (transmission electron microscope) analysis further revealed the formation of supramolecular polymer (monocation radical with cucurbit[8]uril) whose diameter were in the range of several µm as indicated by DLS measurements; however the oxidized form, i.e., the viologen dication with cucurbit[8]uril showed dotted spots in the range of sub nanometer level. The internal periodicities of the supramolecular polymers were analyzed by SAXs (small angle X-ray scattering) measurements. Additionally, we have demonstrated that these supramolecular organic frameworks can be depolymerized by oxidation in air and again can be polymerized (intermolecular radical dimerization) by reduction under inert atmosphere demonstrating that these systems will be of broad interest.

Highlights

Zhang et al reported a two-dimensional viologen based supramolecular assembly formed by viologen radical dimerization which is enhanced by CB[8]27
We report the synthesis of star-shaped ethyl terminated viologen (ESV) and newly self-assembled network of different viologens (EV, EDV, ETV & Ethyl terminated star-shaped viologen (ESV)) driven by radical–radical (V+...+V) dimerization
We reported the 2D supramolecular organic framework formed between the different viologen guest molecules (EV, EDV, ETV and ESV) and CB[8] and the interactions were probed spectroscopically in detail by employing UV-Vis spectroscopy, cyclic voltammetry, Electron Paramagnetic Resonance (EPR) spectroscopy and particle size measurements

Summary

Introduction

Zhang et al reported a two-dimensional viologen based supramolecular assembly formed by viologen radical dimerization which is enhanced by CB[8]27. Zhou et al reported the construction of a three-dimensional viologen based cross-linked supramolecular assembly and they further discussed on the stability of radical dimer with preorganization of rigid building blocks. We report the synthesis of star-shaped ethyl terminated viologen (ESV) and newly self-assembled network of different viologens (EV, EDV, ETV & ESV) driven by radical–radical (V+...+V) dimerization. Further these dimerized species forms a supramolecular polymeric network in the presence of CB[8] and these assemblies were subjected to spectroscopic investigations

Methods

Results

Conclusion