Electrochromic Behavior Of Mono- And Bis-benzyl-substituted Viologens In Deep Eutectic Solvents

Electrochromic devices(ECDs)are essentially a reversible electrochemical cell,and scholars continue to further optimize the composition of the device from the aspects of electrodes,electrolytes,and electroactive materials to better improve device performance.In this paper,disbenzyl viologen(DBV)and monobenzyl substituted viologen(MBV)are used as electrochromic active materials,and choline chlorideethylene glycol(ethaline)deep eutectic solvent is selected as green electrolyte for related research.First,the electrochemical and electrochromic behaviors of DBV and MBV in ethaline solution were characterized by cyclic voltammetry and in situ spectroelectrochemical.The results show that the redox reactions of DBV and MBV in ethaline have good reversibility,and the reduction potential of MBV has an obvious negative shift compared with DBV,and the single component DBV and MBV exhibit electrochromic responses colorless (?) blue and colorless (?) magenta,respectively.And using the different redox potentials and electrochromic color characteristics of both,a multicolor electrochromic response from colorless (?) blue (?) purple was obtained using their mixed solutions.Secondly,the electrochemical behaviors and spectroelectrochemical behaviors of MBV in different acid-base ethaline solutions and ethaline-SiO2 gel were measured by experiment and density functional theory(DFT)calculation.The results show that in an acidic environment,the unsubstituted pyridine nitrogen atoms in the structure will be protonated,so that MBV exhibits an electrochromic response similar to that of DBV;accordingly,it is reasonable to explain the magenta color of MBV in ethaline solution-type devices,the blue color in the ethaline-SiO2 gel device and the magenta color in the ethaline-SiO2-KOH gel device.