Development Of CO₂-based Viologen Derivatives As Electrochromic Materials

The polymerization of CO₂-derived cyclic carbonate with amines is considered the most promising pathway for the production of CO₂-based PUs from the viewpoint of green and sustainable chemistry.Moreover,the resulting PUs contain primary hydroxyl groups in the main chain and a secondary hydroxyl group in theβ-position of the urethane moieties,allowing the existence of strong intra-and intermolecular hydrogen bondings.Such unique features enable them to have high chemical resistance,reduced permeability,and high hydrolytic properties compared to conventional PUs.Currently,the research on the CO₂-based PUs is mainly focused on enhancing their mechanical/thermal properties for their application in thermosets or elastomers.The development of novel green PUs with multi-functions such as stimulus-responsive,inflammable,antibacterial properties to meet diverse applications has become the future trend.Viologen is a kind of organic small molecule compound with bipyridine molecular structure,which is widely used in the electrochromic field because of its good redox properties and structure tunability.In this paper,the authors synthesized a series of carbon dioxide-based viologen derivatives.The molecular structures of the synthesized viologen derivatives were characterized and confirmed by nuclear magnetic resonance spectroscopy and infrared absorption spectroscopy（FTIR）.In this paper,CO₂-derived ionic polyurethane（PUB）and polyurea（PUAB）were successfully synthesized from 4,4’-bipyridine under the conditions of high temperature,high pressure and alkaline catalyst.The structure of the polymer was confirmed by FTIR and NMR.The electrochromic properties of the synthesized viologen derivative electrochromic devices were characterized by electrochemical cyclic voltammetry（CV）and UV-Vis absorption spectra.Finally,the electrochromic properties of CO₂ Based viologen derivatives were studied.Electrochromic device based on polyurethane bipyridyl PUB²⁺（PF₆^-）₂ and polyurea bipyridyl PUAB²⁺（PF₆^-）₂ was assembled.Two indium tin oxide（ITO）glasses were used as working electrodes and counter electrodes to form a sandwich structure of conductive ITO glass/electrolyte（containing CO₂ Based viologen derivatives and ferrocene）/ITO glass.Through the study of the electrochromic device performance of the device,the results show that the coloring efficiency of the prepared PUB at 608 nm is about 137 cm~2 C^-1,and the coloring efficiency of PUAB is 79 cm~2C^-1,which has good cycle performance.In addition,PUB can be degraded under certain conditions.