Structural studies of alkoxysilyl-functionalised ionic liquid and its application in a hybrid electrochromic device

A new sol–gel polymerisable ionic liquid 1-(2-(2-methoxyethoxy)ethoxy)ethyl)-3-(3-(trimethoxysilyl)propylimidazolium iodide was synthesised with the aim of preparing an I−/I3− redox electrolyte. The processes of hydrolysis and condensation were followed first in acidic and basic conditions using ATR IR and 29Si NMR spectroscopy. The IR bands at 1100 and 1126 cm−1, together with the prevailing T3 signal, showed that more branched silsesquioxane structures formed under basic catalysis. The formation of silsesquioxane structures was also followed in situ using two FT-IR techniques, i.e., transmission and reflection–absorption mode. The conductivity of the basically catalysed electrolyte initially reached 4.3 × 10−3 S/cm but stabilised at 1.2 × 10−4 S/cm after condensation. The presence of I3− species was proven by the appearance of νs(I3−) mode at 111 cm−1 in micro Raman spectra and 295 and 370 nm peaks in UV–vis absorption spectra. Finally, the electrolyte was applied in a hybrid electrochromic device that displayed persistent colouring/bleaching during 4240 cycles tested.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Single end-capped alkoxysilyl- and methyldiethyleneoxide-functionalised ionic liquid. ► Basic catalysis led to more branched structures than the acidic one. ► In situ FT-IR measurements of electrolyte in transmission and reflective modes. ► Hybrid electrochromic device displayed persistent optical change during 4240 cycles.