RGB organic electrochromic cells

In this work we present three novel viologen-type electrochromic compounds, which turn into red, green and blue (RGB) upon electrochemical reduction on porous titania surface. The synthesis of the three compounds involved attaching benzyl group with phosphonic acid residue as an anchor to 4,4′-bipyridine, 3,3′-dimethyl-4,4′-bipyridine and 4,4′,4″,4′″-thieno-2,3,4,5-tetrayltetrapyridine. The sterically demanding benzyl groups help to decrease the strong propensity of the colored radical cations to aggregation. The electrochromic derivatives were adsorbed on the surface of porous titania layers prepared by electrophoretic deposition onto a fluorine-doped tin oxide (FTO) glass followed by mechanical compression. Finally the electrodes with the grafted electrochromic derivatives were glued to a second FTO glass to form a closed cell, which operates with two electrodes. The electrochromic windows exhibited high contrast, fast response and low current consumption (∼1 mA) when relatively low voltage (∼5 V) was applied.