Polythiophene-based Electrochromic Material And EC-EFC Bifunctional Polymer

Electrochromism (EC) is broadly defined as a reversible optical change (transmissivity, absorptivity or reflectivity etc.) in visible and infrared region induced by an external voltage, with redox reaction or the injection or withdrawing of electric charge (electron or ion) in molecule interior structure. The macroscopic manifestation is the color and transmissivity change of material. EC material and device increasingly receive attention in recent years due to the broad application prospect in fields such as smart window, smart sunglass, anti-dazzling automobile rearview mirror, and static display. Among numerous kinds of EC materials, polythiophenes EC materials possess many advantages such as stable EC performance, relatively high color contrast, fast response time, relatively high electric conductivity, simple preparation technique, and the capability to achieve multiple color display. Therefore, the research about polythiophenes EC materials has important scientific significance and certain commercial value.This thesis focuses on polythiophenes EC materials. The color, solubility, transmissivity difference and fluorescence characteristic of materials were optimized through changing backbone structure and pendent groups. We designed and synthesized a series of EC materials, characterized and researched the performance of materials and devices, and explored the relationship and regulation between material structure and performance. This thesis comprises the following four portions:In the first portion, we designed and synthesized two polythiophenes EC materials that can be electrochemically polymerized. The monomer of one material is ProDOT-(COCPh)2. The polymer film of this material shows blue in neutral state, and colorless and transparent in oxidized state. The oxidization voltage and reduction voltage are respectively 0.4 V and -0.25 V. This material has features of low driving voltage, fast respond time (1.7 second), and high transmissivity in oxidized state. The transmissivity difference between colored state and bleached state is 77.5%. This EC polymer have certain prospect in applications such as EC window, rearview mirror and static display. The other material is ProDOT-(COCThi)2.The polymer film of this material shows brick-red in neutral state and blue grey in oxidized state. Because this material has two kinds of thiophene of different positions that participate in redox reaction, it has two oxidation voltages (0.54 V and 1.06 V) and two reduction voltages (-0.56 V and 0.4 V). In contrast, although ProDOT-(COCPh)2 has similar structure with ProDOT-(COCThi)2, it only has single oxidation voltage and reduction voltage. This difference about redox peaks indirectly demonstrated that the benzene ring doesn’t participate in the ionic doping and dedoping processes.In the second portion, we synthesized a kind of solution-processable polythiophenes EC material that can be spray-coated with Stille coupling polymerization process. This material is alternating polymer based on bithiophene and 3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine. The latter one bears long-chain alkoxy group, which can endow this conjugated polymer with good solubility in low-boiling-point solvent. This material can be switched between purple and colorless transparency, and has features such as simple synthetic method, high contrast, low driving voltage, fast respond time, and long cycle life. Furthermore, we assemble an EC device by taking this material as working electrode, and V2O5 film as counter electrode, and researches its performance.In the third portion, we designed and synthesized a series of D-π-A type polythiophenes EC materials P1, P2, P3 and P4. They are based on triphenylamine with different pendent groups and long-chain alkoxy substituted thieno[3,4-b][1,4]dioxepine. The four polymers all have good solubility in low-boiling-point solvent. It was found by research that, pendent groups with different electron-withdrawing strength could exert regular influence on polymers’optical absorption properties, fluorescence property, electronic energy level and EC performance. The four polymers have different colors and low oxidation voltages, and they all exhibited relatively large transparency difference at 890 nm around. Among them, P3 and P4 have no fluorescence when they were dissolved in THF but have strong fluorescence in film state. This is an aggregation-induced emission (AIE) phenomenon.In the fourth portion, based on previous work, we constructed novel conjugated polymer ProDOT-TPE with 3,3-bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine and typical AIE molecule tetraphenylethene. The target polymer has good solubility, meanwhile has EC property and AIE performance. More importantly, the EC device prepared with this polymer, its color and fluorescent state can be synchronously driven by relatively low voltage (±2.5 V), namely is can achieve electrochromic-electrofluorochromic (EC-EFC) bifunction. The device exhibits navy blue in oxidized state, simultaneously the fluorescence disappears; in reduced state, the device becomes yellow, and the fluorescence comes back. Strong fluorescence can be observed under UV light. This unique performance endow the material with special potential in EC-EFC bifunctional application.