Electrochromic Visual Indication of Levodopa Level on the Basis of Tuning the Electrochromic Performance of Benzyl Viologen via Phenol Combined With Amine

The possibility of an electrochromic platform for the visual detection of target molecule has been proven in our previous work. In this article, levodopa, which bears a phenol combined with amine, is envisaged as an extension of research. Levodopa is added into the electrolyte gel of the electrochromic devices based on benzyl viologen. We found that levodopa can improve the electrochromic performance of benzyl viologen. Levodopa reduces the driving voltage of the electrochromic device to −1.2 V, in comparison to that of −2.4 V without levodopa. The optical contrast of the device at 535 nm increases dramatically with the introduction of levodopa under the same condition. The coloration time of the device in the absence of levodopa can be shortened from 67.7 to 14.2 s with this compound, and the bleaching time decreased from 1030.4 to 874.6 s. The coloration efficiency of the as-fabricated devices at 535 nm can reach from 23.93 cm 2 ·C − 1 (benzyl viologen-only) up to 73.91 cm 2 ·C − 1 (with levodopa). It is interesting to note that the coloration of the electrochromic devices evolves as a function of the concentration of levodopa from 1.0 × 10 − 6 to 2.0 × 10 − 2 mol·L − 1 at a fixed driving voltage, giving a linear relationship between RGB chrominance values and logarithmic of levodopa concentrations, showing the possibility of electrochromic visual indication. This article demonstrates levodopa can enhance the electrochromic performance of benzyl viologen and also holds promise for visual indication of levodopa level.