Synthesis And Electrochromic Properties Of Viologen Derivatives

Electrochromism refers to an optical phenomenon in which the color of a material undergoes a reversible change under the action of an applied voltage.Electrochromism is widely used in fields such as optical modulation,flexible wearables,displays,energy storage,and sensing.In recent years,viologen has been favored by researchers in the field of electrochromism because of its easy modification of molecular structure,rich color changes,low driving voltage and high coloring efficiency.The structural modification of viologen by substitution reaction can regulate its properties.At present,the structural modification of viologen mainly involves introducing conjugated groups or bridging elements between two pyridine units,and studying their impact on electrochromic performance.This article starts with the nitrogen atom of pyridine and introduces alkyl chain substituents at one or both nitrogen atoms.It compares and analyzes the effects of factors such as the length of alkyl chains,symmetric and asymmetric substitutions,on their electrochromic properties.The main research content is as follows:(1)Unilateral asymmetric viologen derivatives were designed and synthesized and used in gel electrochromic devices.The effect of alkyl chain length on the electrochromic properties of viologen derivatives was investigated.Two asymmetric viologen derivatives were synthesized using 1,2-di(4-pyridyl)ethylene as raw material by bonding the alkyl chain only at the pyridine nitrogen atom on one side and changing its carbon chain length.A novel organic electrochromic gel was prepared by introducing asymmetric viologen derivatives into polymethyl methacrylate gel as electrochromic active substances.Using ITO conductive glass as the upper and lower electrodes,an electrochromic device with a "sandwich" structure was packaged.Under the action of external voltage,these two asymmetric viologen derivatives exhibit similar color changes and can reversibly switch between colorless and peach red.Among them,viologen derivatives with long alkyl chain substituents have better electrochromic performance,and their optical contrast,response time,and coloring efficiency have been improved to a certain extent.(2)We designed and synthesized bilaterally substituted symmetric viologen derivatives and studied their electrochromic properties.Similarly,using 1,2-di(4-pyridyl)ethylene as the raw material,the alkyl chain is bonded at the pyridine nitrogen atoms on both sides,and hydroxyl groups are introduced at the end of the alkyl chain to synthesize symmetric viologen derivatives.The symmetrical viologen derivative was introduced into the polymethyl methacrylate gel to prepare the electrochromic gel,which was encapsulated as an electrochromic device.Under the action of external voltage,symmetrical viologen derivatives can reversibly switch between colorless and rose pink.Compared with asymmetric viologen derivatives,symmetric viologen derivatives have more excellent electrochromic properties,and their optical contrast has been significantly improved,reaching up to 70.5 %.