A study on the electro-optical properties of HV and TMPD with their application in electrochromic devices

The systematic exploration on the electro-optical properties of viologen and its application to the solution-type complementary electrochromic device (ECD) was studied. Heptyl viologen (HV) and N,N,N',N'-tetramethyl-1,4-phenylenediamine (TMPD) were chosen as a cathodic and anodic electrochromic material, respectively. Suitable darkening potentials for HV2+ and TMPD were determined to be -1.3 and -0.3 V (vs. Ag/AgClO4), respectively, according to voltammetric and spectroelectrochemical measurements. The coloration efficiency of HVcircle+ at 615 nm was measured to be 100.5 cm(2)/C by the gavanostatic method. The molar absorptivity of TMPDcircle+ at 615 nm was calculated to be 9210 M(-1)cm(-1). A solution-phase ECD was fabricated by sandwiching both HV2+ and TMPD in between two parallel indium tin oxide (ITO) electrodes with an intervening space. At 615 nm, a typical transmittance change of over 70% was observed under darkening voltage of 1.0 V and the corresponding coloration efficiency was 133 cm(2)/C for the ECD. Self-bleaching was possible under an open circuit condition.