Electrochromic Devices with Panchromatic Absorption Based on Novel Asymmetric Viologens with Anthraquinone Unit
| Autor: | Kuan-I Chen, 陳冠逸 |
|---|---|
| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 Viologens, also referring as 1,1''-disubstituted-4,4''-bipyridiniums salts, are electrochromic (EC) materials that gain much attention for their dramatic and highly reversible EC properties in recent years. Viologens possess two reactive nitrogen atoms on its bipyridine part, different functional groups can graft onto them and become their substituents. They would be regarded as symmetric viologens when the two substituents of them are the same. In contrast, they would be regarded as asymmetric viologens when the two substituents of them are different. The main idea of this thesis is to graft an anthraquinone unit and an aryl group onto viologen. Aryl viologens often lack absorbance at about 530 nm light wavelength, while anthraquinone happens to provide absorbance at about 530 nm light wavelength. Therefore, we would combine aryl viologens and anthraquinone unit and synthesize novel asymmetric viologens, expecting to produce panchromatic absorbance. In this case, the proposed viologens could stand out from most of the other viologens, which could only produce blue or green color. In Chapter 3, we would choose anthraquinone unit and p-cyanophenyl group as the two substituents of the asymmetric viologen. Differ from other viologens, which only have two redox pairs in their cyclic voltammetric curve, our asymmetric viologen have three redox pairs in its cyclic voltammetric curve, indicating anthraquinone unit also involves redox process as we applied voltages. Through combining the asymmetric viologen with a redox mediator, ferrocene, the electrochromic device (ECD) was fabricated. The ECD could give 65.0% transmittance change (ΔT%) initially at 530 nm light wavelength when being switched between −1.3 V and 0 V. Fast response times (3.05 s in coloring and 1.89 s in bleaching) were observed. Meanwhile, good long-term stability can be obtained after adding polymers into electrolyte to increase the viscosity, maintaining 83.3% of its initial ∆T% after 10,000 continuous cycles. In addition, the apparent diffusion coefficient (Dapp) of the ECD was calculated by Cottrell equation, and the working mechanism of the ECD was also determined. In Chapter 4, pursuing a better long-term stability is always an ambitious goal for researchers investigating ECDs. Therefore, we decided to further improve the long-term stability of the viologen in Chapter 3. We chose anthraquinone unit and 4-tert-butylphenyl group as the two substituents of the asymmetric viologen. From the reported literatures, we found out that the long-term stability could be improved as the substituents of viologens get bulkier, bulkier substituents can prevent viologens from aggregation or forming dimers. The electrochemical properties of the proposed viologen in Chapter 4 are nearly the same with the one in Chapter 3, with only a little decay in the ability of reaching panchromatic absorbance. The possible reason may due to the different inductive effect among the functional groups. The proposed ECD in Chapter 4 could finally retain 95.0% of its initial ∆T% after 10,000 continuous cycles under the same condition with the one in Chapter 3. At the end, Raman spectra data was provided to compare the signals between the viologens in Chapter 3 and Chapter 4, this data provide a direct evidence that by changing the substituents of viologens can actually affect their tendency to form aggregates or dimers and thus further affect their long-term stability. In this thesis, we successfully produced ECDs with panchromatic absorption by combining anthraquinone unit and viologens, making the color of viologen-based ECDs diverse, and discussed the influences on the color and long-term stability of ECDs when anthraquinone unit combined with different viologens. In addition, this thesis also proved that the idea of combining two different EC materials is implementable. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|