Donor-acceptor Type Conjugated Polymers For Applications In Electrochromic Devices

Electrochromic (EC) is defined that a material takes place reversible redox reaction or electrical charges (electrons or ions) injected or ejected and its optical properties (transmittance, absorption and reflectivity) exhibit reversible changes in visible light region. The macro performance for molecules display that the reversible changes of the color and transparency of these changes. Being modified by designing molecules structure, donor-acceptor type electrochromic polymers are paid attention for a wealth of sources, low cost, low driving voltage, good optical quality, fast color conversion and long working stability.In this article, we studied that the synthesis, characterization and properties of donor-acceptor type electrochromic polymers by modifying the donor units and acceptor units. We measured the properties of the electrochromic polymers and chose the counter electrodes which electrical charges matched with the polymer working electrodes. We characterized and optimized the electrochromic properties of devices, to obtain devices with multi-colours, high optical contrast, fast response switching times. The study work below were undergoing through four parts:In the first part,8,11-Di-(4-thiophen-2-yl)acenaphtho [1,2-b]quinoxaline (DTAQ) was successfully synthesized by Stille coupling reaction and the corresponding polymer was prepared electrochemically. Electrochromic properties of the polymer film reveal that PDTAQ film show distinct color states and high optical contrast accompany fast switching times. The complementary ECDs which are based on the PDTAQ film as working electrode, prussian blue (PB) and V2O5as counter electrode respectively. LiClO4/PC solution as electrolyte were assembled and characterizaed. The results illustrate that the properties of PDTAQ/PB device and PDTAQ/V2O5devices (including the absorption, color changes,△T%and response times) can be adjusted by the counter electrodes.In the second part, a novel donor-π-bridge-acceptor copolymer, PBDTTPA-CHO, containing4-(Bis(4-bromophenyl)-amino)benzaldehyde and4,8-bis-(2-ethyl-hexyloxy)-oxybenzo-[1,2-b:3,4-b’]dithiophene was successfully synthesized using Stille coupling polymerization and the pendant aldehyde group was modified with cyanoacetic acid to synthesize another polymer, PBDTTPA-COOH. Both of polymers are soluble in ordinary organic solvents so that they can be easily made films onto rigid or flexible substrates. The polymers with different electrophilic groups exhibit different electrochromic behaviors, including applied driving voltages, completely different colors and switching transmittances. We fabricated and studied the sandwiched ECDs using a PBDTTPA layer as the working electrode and vanadium pentoxide film acted as the counter electrode. Upon the contribution of counter electrodes, devices of both polymers show similar color changes but higher transmittance than their films.In the third part, star branched monomers2,4,6-tris(4-(3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin-6-yl)-phenyl)-1,3,5-triazine (M1) and tris(4-(3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]-dioxepin-6-yl)-phenyl)amine (M2) were designed and successfully synthesized via Stille coupling reaction and the corresponding polymers (PI, P2) were synthesized using electrochemical polymerization. Structures of both of the monomers were certified by NMR and FT-IR. p1and P2, having electron-withdrawing and electron-donating core respectively, display various electrochromic behaviors, including distinguished colors, applied driving voltages and switching transmittances. Therefore, this part provided a new method for electrochromic molecules design.In the fourth part, a series different side chains of donor-acceptor (A1-D-A2) conjugated copolymers with a donor unit (benzo[1,2-b:4,5-b’]dithiophene (BDT)) and two different electron-accepting untis (N-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) and dithiophenebenzothiadiazole (DTBT)) is designed and prepared. The series of polymers display two intense absorptions in the wavelength range of600-900nm, and the band gaps (Eg) are lower than1.70eV. The optical and electrochemical properties of these polymers show that the copolymers have the low band gaps and the HOMO and LUMO energy levels are different. The results indicate that different soluble alkyl chain can optimize the properties of the copolymers, which are potential in conjugated polymer electrochromic materials and devices.