Tuning the Electrochromic Properties of Poly(alkyl-3,4-ethylenedioxyselenophenes) Having High Contrast Ratio and Coloration Efficiency

A systematic study of the electrochemical, spectroelectrochemical and electrochromic (EC) properties of poly(alkyl-3,4-ethylenedioxyselenophene) (PEDOS-C-n) (n = 0, 2, 4, 6, 8 and 12) films is reported. The alkyl substituents lead PEDOS-C-n films to exhibit sharper redox peaks than the parent PEDOS film and raise an onset of their oxidation potentials by 0.20-0.62 V. As expected, the introduction of alkyl chains significantly improves the EC properties and the electrochemical stability of PEDOS-C-n films and results in high contrast ratios and coloration efficiencies, low switching voltages, and fast switching times. As the length of the alkyl chain increases, the broad absorption peak of PEDOS sharpens and splits into three distinct peaks for PEDOS-C-n films starting from n = 4. We have identified the correlations between EC properties (such as coloration efficiency) and other observed properties of PEDOS-C-n films (such as their peak width, the position of the maximum absorption peak, the ratio of the absorption intensity of NIR spectra peaks to visible spectra peaks) and the contrast ratio. Interestingly, EC properties show bell-shaped behavior as a function of alkyl chain length, which reaches the maximum for PEDOS-C-6 film, whereas the EC properties of films with shorter and longer alkyl chains are poorer.