Visible to near-IR electrochromism and photothermal effect of poly(3,4-propylenedioxyselenophene)s

A new selenophene derivative, 3,4-propylenedioxyselenophene (ProDOS), was electropolymerized to a polymeric thin film which demonstrated wide spectral tunability from the visible to near-infrared (NIR) region. The anodic and cathodic peaks of the polymeric ProDOS (PProDOS) were observed at +0.22 and -0.30 V, showing a narrow band gap. In the visible region, the PProDOS film showed color change from navy blue in its dedoped state (-0.12 V vs Ag/AgCl) to highly transparent pale gray green in its doped state (0.68 V vs Ag/AgCl) with a high coloration efficiency (CE) of 273 cm² C^-1 and large transmittance change (contrast ratio of 5.7). The color change of the PProDOS film by electrochromism in the visible region was simultaneously accompanied by NIR electrochromism. Upon exposure to a NIR source (0.7 W cm^-2), the doped PProDOS film resulted in a temperature rise of 10.7 °C compared to that of the bare indium tin oxide (ITO) coated glass, while the navy blue colored PProDOS film experienced a temperature rise of 10.2 °C. This photothermal effect by NIR light exposure was switchable between the colored and bleached state by simply dedoping and doping the film electrochemically, respectively. Furthermore, bleached PProDOS particles dispersed in water (0.05 mg mL^-1) also showed a high photothermal effect (2 W cm^-2) with a temperature rise of 13.1 °C, as compared to pure water. Compared with poly(3,4-ethylenedioxythiophene) (PEDOT), it was found that the new selenophene polymer (PProDOS) provided efficient visible to NIR electrochromism in addition to the high photothermal effect, resulting in a large temperature rise and heat conversion upon exposure to a NIR source.