Preparation And Properties Of Green Electrochromic Polymer Based On Quinoxaline And Three-Electrode Device

Recently,electrochromic materials as new functional materials have shown broad commercial application prospects on the display field.Multicolor-showing characteristics are critical for the application of electrochromic materials and devices.Among electrochromic materials,conducting polymers have attracted wide attention owing to their various advantages,such as easy tuning,rich color changes,fast switching speed,high optical contrast and low cost.As one of the three primary colors?red,green and blue?,it's difficult to synthesize green electrochromic polymers.The reason is that the polymer should contain two characteristic absorption peaks in the visible region?located near 400 and 700 nm,respectively?,and also change with voltage.Therefore,the design and synthesis of novel green polymers is of great significance for the development and large-scale application of electrochromic materials and devices.Donor-Acceptor type polymers can regulate their energy gaps and control the color-showing by changing the D or A structures.In this thesis,a new D-A type monomer was obtained by the rational structural design,and the neutral green polymer film was prepared via electrochemical polymerization.Based on this,a new electrochromic device with three-electrode structure was designed and assembled to realize the multicolor display.In the first part,a D-A conjugated monomer[5,8-bis?2,3-dihydro[3,4-B][1,4]dioxin-5-yl?-2,3-dual?4-?hexadecyloxy?phenyl?quinoxaline?BOPEQ?was designed and synthesized based on a quinoxaline derivative as acceptor unit and3,4-ethylenedioxythiophene?EDOT?as donor unit.The poly?3,4-ethylenedioxythiophene?:polystyrene sulfonate?PEDOT:PSS?was introduced as electrode interface layer.The PBOPEQ and PBOPEQ-PEDOT:PSS films were prepared via the electrochemical polymerization.Scanning electron microscope?SEM?shows that the PBOPEQ film presents obvious local cracks and ridges structures,while the PBOPEQ-PEDOT:PSS film presents a stacked porous structures.Besides,the ultrasound tests further confirms the PEDOT:PSS interface layer can improve the interface adhesion between the polymer film and the electrode and brings out a better film-forming ability of the polymers.The cyclic voltammetry curves shows that PBOPEQ-PEDOT:PSS film has a better redox activity and charge storage capacity compared to the PBOPEQ film.From the electrochromic performance tests,it can be found that the PBOPEQ-PEDOT:PSS film exhibits higher optical contrast??40%?and better coloration efficiency(230.84 cm²?C^-1)compared with PBOPEQ film(?25%and131.84 cm²?C^-1).In addition,the PBOPEQ-PEDOT:PSS film possesses good stability?retains?90%of its original transmittance after 5000 s?and excellent memory effect behavior?in the oxidation state,the transmittance retains hardly change within 36hours without external voltage?.In the second part,the green polymer film PBOPEQ-PEDOT:PSS as the electrochromic layer 1,the red polymer film poly?3,10-bis?2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl?-1-dodecyl-1H-phenanthro[1,10,9,8-c,d,e,f,g]carbazole??PDEP?synthesized by our research group as an electrochromic layer 2,and pre-oxidized polyaniline as an ion storage layer?Ox-PANI?,were utilized to assemble a new electrochromic device with three-electrode structure ECD?PBOPEQ-PEDOT:PSS/Ox-PANI/PDEP?.As comparison,the electrochromic layer 1and ion storage layer?Ox-PANI?were used to assemble two-electrode device ECD1?PBOPEQ-PEDOT:PSS/Ox-PANI?,and the electrochromic layer 2 and ion storage layer?Ox-PANI?were used to assemble two-electrode device ECD2?PDEP/Ox-PANI?.The results indicated that the new three-electrode device ECD?PBOPEQ-PEDOT:PSS/Ox-PANI/PDEP?shows multi-colored changes?color changes from brown to red to cyan to blue?compared to two-electrode devices ECD1?color changes from green to transparent?and ECD2?color changes from red to blue?.Therefore,this new structure device with three-electrode provides a new research idea for design and preparation of multicolor or even panchromatic display.