Synthesisand Electrochromic Properties Of Metallo-Supramolecular Polymers

Being applied in a large of areas,such as anti-glare mirrors and glasses,indicators and labels,smart windows,electronic papers,and information storages,electrochromic materials（ECMs）have received widespread interests as molecular switches for optical and electronic applications.Recently,metallo-supramolecular polymers,as a novel emerging ECM,has attracted special attentions for it has strong optical contrast,high coloration ability,fast response time and low switching potential.Two kinds of metallo-supramolecular polymers named FeL,FeL3 were synthesized by the stepwise complexation of an Fe（II）salt with a linear bis（terpyridine）ligand and a branched tris（terpyridine）ligand.A 3-D wrinkled structure of FeL3 was supported by the SEM images.The two polymers had a blue color based on the metal-to-ligand charge-transfer（MLCT）absorption.Both of them exhibited excellent electrochromic property with absolutely reversible color change between blue and colorless by the redox reaction of Fe ions.This means that the electron transfer rate is almost the same as the diffusion rate of the counter anions during the redox.During the color change,the polymer FeL3 has high optical contrast（ΔT>60%）,fast response time（less than 1s）,high coloration efficiency（more than96.9 cm2/C）.Using Propylene Carbonate（PC）as organic solvent,sodiumperchlorate（NaClO₄）as metal salt,the gel electrolyte film PMMA-PC-NaClO₄ was prepared by sol-gel technique.It is found that the highest ionic conductivity of8.3 × 10-4S/cm is achieved with the NaClO₄ concentration of 1.4mol/L.The gel electrolyte has high optical transparency（>90%）,good thermal stability,certain adhesion and high electrochemical stability window（about 5.0V）.Using the above materials,the all solid symmetric（ECD-1）and asymmetric electrochromic（ECD-2）devices were assembled.The optical contrasts of them are80% and 42.5%,respectively.For the ECD-2,the color overlay effect occurred during the test,compared with ECD-1,the initial state of blue colour is deepened,the fading state is superposed to dark green,and the electrochemical performance is more stable.After 500 switching cycles,the electrochemical performance did not decline greatly.In addition,we found the electrochromic device can be seen as a rechargeable thin film battery,the discoloration process can be seen as charging,and the coloration process can be seen as discharge.