Multifunctional Materials Based On Electrochromic Polymers

Electrochromism(EC)refers to the optical properties(transmittance,absorption,reflectance,etc.)of materials are stably reversible under the applied electric field,ie,external manifestation is the apparent change in material color or transparency with the doping and undoping of the material.This excellent electrical response makes it more and more attractive to researchers in fields such as smart windows,anti-glare mirrors,and static displays.Among them,electrochromic polymer materials(conjugated polymers)are gradually accessed to commercialization and daily life from the laboratory in small doses because of their unique advantages,such as high coloring efficiency,fast response time,easy preparation and the ability to achieve multi-color control through molecular structure adjustment.Nowadays,many researchers not only focus on the electrochromic properties of materials,but also attach great importance to the combination of electrochromic properties and other special properties so as to utilize the excellent properties of the material more widely,such as photoluminescence,electroluminescence,super-capacitors,and self-powered materials have been introduced into electrochromic field to expand the application of electrochromic materials.Therefore,this dissertation focuses on polythiophenes electrochromic polymer,by changing the structures of main chain and side chain of the polymer or forming new composite material with other materials such as quantum dots,to obtain electrochromic materials capable of simultaneously achieving multi-functionality.This dissertation systematically introduces the synthesis and characterization of such polythiophene materials,and the assembly of devices based on these materials.It explores the correlations between the structures and properties of materials,and is divided into the following five parts:In the first section,we have synthesized a series of solution-processable electrochromic polymers bearing trifluoromethyl group.These polymers possess excellent solubility in conventional organic solvents just as the polymers with long side chains.Moreover,P1-P3 polymers can be switched from a coloring neutral state to a transmissive doped state,and their electrochromic response characteristic and hydrophobicity are comparable with the P4 polymer,while having enhanced thermal stability.This study develops a novel strategy to design the solution-processable electrochromic conjugated polymers and the synthesized polymers without long side chains could be good candidates for large scale electrochromic application.In the second section,a novel composite CdSe QDs/polymer film was designed to simultaneously achieve trifunctional effects of electrochromism,electrofluorescence and light-induced coloration.Combining the advantages of both quantum dots and conjugated polymer,the formed composite film reveals excellent electrochromic performance with the oxidation and reduction potential of 0.35 V and 0.1 V respectively,the largest transmittance change of 50%in visible region,and the response time within 1.2 s.In addition,the composite film can switch between the non-fluorescent state and fluorescent state,whose PL intensity is more than twice that of pristine polymer film.Further,the material can gradually get self-colored from bleached state under the irradiation of sunlight.Therefore,the trifunctional composite film material could be a new idea for energy-saving electrochromic and fluorescent device in the future.In the third section,a series of novel conducting conjugated yellow-to-transmissive electrochromic and electro fluorescent polymers were designed and synthesized to investigate the structure-property relationship.With side chains of slight different steric hindrances,the polymers present similar yellow color and emit tuned fluorescence with applied reduction potential,and they can turn to nearly transparent state and non-fluorescent state with oxidation potential.The device containing various polymers was also fabricated which can achieve electrochromic and electrofluorescent switching simultaneously,making these polymers be promising candidate for electro-bifunctional material.In the fourth section,a new designed polymer utilizing biphenyl in polythiophene backbone to form twisting conformation was synthesized,achieving bifunction of electrochromic and electrofluorochromic switching synchronously.The polymer can emit intense fluorescence in both solution and solid state while remaining excellent electrochromic properties.With applied external potential,the sprayed polymer film can switch to trans-parent state(non-fluorescent state)from yellow color(fluorescent state).Furthermore,the fabricated device containing this polymer can also realize reversible electrochromic and electrofluorochromic switching simultaneously,and the largest transmittance change of device is 35%.All above pave the way for designing bifunctional materials applied in optoelectronic field.In the fifth section,the designed and synthesized conjugated electrochromic polymers bearing triphenylamine or phenothiazine group can achieve color controlling for both reduction and oxidation states with applied external potential.With incorporation of side anode electrochromic group,the polymers can achieve grey-blue color or dark purple color for oxidation state.The reduction colors of electrochromic polymers can also be controllable with adjustment in polymer backbone structure.Therefore,the obtained polymers can realize switching between two designed colors.All these polymers can reveal comparable transmittance change and moderate switching time.It can systematically provide an effective approach for designing novel electrochromic polymer materials.Additionally,the polymers bearing triphenylamine group as light absorber and power source,can further achieve light induced coloration effect.Thus,these polymers can also broaden a way for energy saving material application range of electrochromic polymers.