The Synthesis And Properties Study Of Solution Processable Electrochromic Polymers Based On Dioxythiophene

Electrochromism (EC) is defined as materials undergo reversible redox reaction by external potential and their optical properties (transmittance, reflectivity and absorption) exhibit reversible changes, inducing the switching of materials’color. The polymer electrochromic materials are paid more attention owning to their fast response time, vivid color and high contrast ratio. With the requirement of big area electrochromic device, solution processable electrochromic polymers exhibit obvious advantages. These polymers could be solved in conventional organic solvents and their films can be prepared by solution processable methods such as spray-coating, spin-coating and ink-jet printing. The research focus of solution processable electrochromic polymers is the development of materials with new color and enhancement of prepared materials properties.In this thesis, we focused on dioxythiophene system. We designed and synthesized a series of solution processable electrochromic polymers based on dioxythiophene. The acyclic dioxythiophene derivatives were investigated to understand the relationship of structure-properties. Red-to-transmissive solution processable electrochromic polymers were exploited and black-to-transmissive solution processable electrochromic polymer films were obtained. Then a series of dioxythiophene derivatives with six-member ring structure were synthesized. In our thesis, the design ideas, synthetic procedures and varies properties were presented in detail. The thesis consists of four sections.In section 1, five acyclic dioxythiophene derivatives with different substituents were synthesized and corresponding polymers were prepared by the oxidative polymerizaion using ferric trichloride. The structure-properties relationship indicates that the linear chain substituent would relieve the steric hindrance of polymer structure compared to branched chain, enhancing the structure order, increasing the mean conjugation length and red-shifting the max absorption wavelength. Four polymers were studied. They exhibit good electrochromic properties and high contrast ratio. Poly(3,4-di(2-ethylhexyloxy)thiophene) (PDEHOT) performs orange color, which could be utilized to prepared red-to-transmissive switching materials.In section 2, we utilized the DEHOT mentioned above and chose 3,4-ethylenedioxythiophene (EDOT) unit to synthesize red-to-transmissive solution processable electrochromic polymers and the polymers’color can be adjusted by changing the ratio of DEHOT to EDOT. Three polymers present orange-red, red and red-purple colors in their colored states and they possess high contrast ratio and decent stability. Then we chose new units-seven-member ring structure. The co-polymerization of DEHOT and seven-member ring structure also obtained near red-to-transmissve polymers, demonstrating the availability of this methods. We conducted investigations on one of four polymers and fabricated corresponding device. The device could switch between red and transmissive states and possess good stability.In section 3, black-to-transmissive solution processable electrochromic polymer films were prepared according to the color mix theory. Two solution processable materials with complementary colors, purple-red and green color, were synthesized and co-processed to obtain black to transmissive films. The mixture films combined the absorption features of purple-red and green color polymers, possessing the homogeneous absorption across the whole visible spectrum, and resulting in the black color.In section 4, the main content is about the solution processable derivatives from EDOT. We introduced three kinds of EDOT derivatives-mono-substituted derivative, bis-substituted derivative and novel mono-substituted derivative. The mono-substituted derivative could switch between dark purple-blue and transmissive states. The bis-substituted derivative switched between blue and transmissive states, which keep the same with PEDOT. Three polymers from the novel mono-substituted derivative exhibit purple-red, blue-purple and deep blue color in the colored states respectively...