Synthesis And Electrochromic Properties Of Dibenzothiophene/Dibenzofuran-thiophenes Copolymers

Electrochromism(EC)is defined as the wonder that optical properties(transmittance,reflectance,absorption,etc.)of the materials undergo reversible and stable change along with colour change when the potential is applied.In recent years,the research has been focusing on improving the properties of electrochromic materials,which is the core problem in EC field.Electrochromic materials based on conducting polymers have drawn much attention due to the better turing ability of structure and colour,thin film flexibility and low-cost effectiveness.Further,the conducting polymers of dibenzo-five-number rings such as polyfluorenes and polycarbazoles as electrochromic materials have achieved great success in colour changes and coloration efficiency,which played important role in EC.Similar to carbazole/fluorene,DBT and DBF display good rigid planarity and excellent fluorescence properties.Given that,they were widely utilized in constructing new host materials of OLED and OFET devices,however,none did EC.We believe that it is apparently a challenge to synthesise and explore the DBT/DBF-based hybrid polymers with interesting electrochromic properties.As we all know,thiophenes has been discovered combining high conductivity,low oxidation potential,good electrochemical properties and unusual thermal stability in the oxidised state,which were introduced into 2,8-points of DBT and DBF,resulted in a series of DBT/DBF-based electrochromic polymers.Special studies and conclusions were as follows:1.DBT/DBF-EDOT electrochromic polymers have achieved reversibly transform between purple in the oxidized state and yellow in the reduced state.PEDOT as star material in conjugated polymers exhibited high stability and electron-rich ability,was introduced into DBT and DBF to synthesis DBT-EDOT and DBF-EDOT.Both monomers showed photoluminescence phenomenon with low oxidational potential of 0.91 V and 0.95 V.The colour changes between purple and yellow,but that,unfortunately,the optical contrasts were bad which may due to the poor stability.2.DBT/DBF-thiophene electrochromic polymers have widely improved electrochromic properties.To abtain outstanding electrochromic polymers with high optical contrasts and coloration efficiency,thiophene was introduced into DBT and DBF to synthesis DBT-Th and DBF-Th.The electrochromic properties of PDBT-Th and PDBF-Th were better than those of PDBT-EDOT and PDBF-EDOT.Particularly,optical contrasts of PDBT-Th in near-IR reached 47%.The introduction of thiophene improved the electrochromic properties than introduction of EDOT which were attributed to low molecular weight and more polymerization units.3.DBT/DBF-alkylthiophene electrochromic polymers have optimized their electrochemical and electrochromic properties along with the increase of alkyl chain,which broadened electrochromic application in the visible region.Base on the research of DBT-Th and DBF-Th,furher studied of DBT/DBF-alkylthiophene electrochromic polymers were achieved.With the increase in the length of alkyl chain attached to the thiophene unit at 3-position,therefore,electron cloud densitythe increased;the onset oxidation potential and reversible redox couple shifted to a lower potential gradually.All of these polymers exhibited different colours(dark blue,light blue,yellow,light grey),and as the length of the side chain increases,transmittance and colouration efficiency were satisfactory step by step especially for DBT-base polymers.In particular,as an excellent blue-to-transparent gray polymeric electrochrome,PDBT-3HexTh exhibited the highest colouration efficiency(304 cm2 C-1 a)with transmittance of 69%among all these type systems.4.The electrochemical and electrochromic properties of PDBT-30ctTh were comparatively investigated in different media and revealed the effect of media.DBT-3OctTh exhibited different electrochemical and electrochromic properties in DCM,PC,and BFEE.Particularly,in BFEE,DBT-30ctTh revealed the lowest onset oxidation potential(0.67 V vs.Ag/AgCl).Doping level was calculated to be 0.32 in DCM,0.12 in BFEE and 0.04 in PC,respectively.The colours are similar to each other of PDBT-3octTh in different media.Moreover,the lowest band gap was obtained in PC media.In conclusion,this thesis was supported by DBT/DBF bybrid with EDOT,thiophene,and alkylthiophenes.These 11 monomers were electropolymerized to their responding polymers,the electrochromic properties of which were systematically researched.The thesis provided a valuable guidance of electrochromic materials based on dibenzo-FIve-member ring conjugated polymers.