Novel quinoline-pyridine type viologens for near-infrared electrochromic devices

In this work, four novel viologen derivates (PTV, PTMV, TPTMV and FTPTMV) consisted of the similar backbone with one pyridine unit and one quinoline group were developed for all-in-one electrochromic devices. Different from the conventional viologens, four viologen derivates in this work showed stable transmittance and significant color changes throughout the electrochromic process. Under the stimulation of external voltage, the four derivatives can show changes from colorless to dark yellow-green. Specially, PTMV, TPTMV and FTPTMV with bulky and rigid moiety (norcamphor or camphor) demonstrated efficient near-infrared (NIR) electrochromic performance around 890 nm, involving high optical contrast over 90 %, high coloration efficiency over 150 cm² C⁻¹ and excellent cycling stability (remaining over 90 % after 2000 switching cycles). In addition, it also demonstrated outstanding performance in testing large-area devices. This work provided an effective strategy to molecular design of viologen derivates for NIR electrochromic devices with potential application in smart windows.