Study On Preparation Of Ester Substituted Polythiophene Derivatives Via Direct C-H/C-H Coupling Polycondensation

Ester substituted polythiophenes have good optical and electrical properties,which is an important conductive polymer material and has been widely used in organic photovoltaic,field effect transistor,LED and other fields.Direct C-H/C-H conjugated polycondensation catalyzed by transition metal is a new method to prepare conjugated polymers in recent years.The synthesis process does not require any pre-functionalization of monomers.Conjugated polymers can be obtained directly through C-H bond coupling in aromatic monomers,showing high atomic economy and environmental friendliness.However,there are some shortcomings such as long reaction time（usually 24-72 h）,low molecular weight（the average molecular weight is less than 20 k Da）and poor regioregularity（the highest HT is about 85%）in the preparation of ester substituted polythiophene by this method.In response to the above issues,this paper proposes two research ideas:1)introducing new nitrogen or phosphorus containing ligands into the catalytic system,coordinating with metal Pd to stabilize intermediates,thereby improving reaction efficiency and improving the regioregularity of polymers;2)Combining microwave technology with C-H/C-H coupling polymerization to improve reaction efficiency and shorten reaction time.The main research content is as follows:1)Construction of catalytic system involving organophosphine ligands and preparation of ester substituted polythiophene by direct C-H/C-H coupling polycondensation.Four phosphorus containing compounds,namely bis（diphenylphosphine）methane（L1）,1,2-bis（diphenylphosphine）ethane（L2）,1,3-bis（diphenylphosphine）propane（L3）and 1,4-bis（diphenylphosphine）butane（L4）,are used as organic phosphine ligands,which are added to the catalytic system with Pd（OAc）₂ or Pd Cl₂ as catalyst,Ag₂CO₃ as oxidant and KOAc as base,respectively,The effects of different ligands and catalyst/ligand ratios on the direct C-H/C-H coupling polycondensation reaction of octyl-3-thiophenecarboxylate were systematically studied.The research results show that the addition of organic phosphine ligands significantly improves the efficiency of the condensation reaction.Under the condition of a molar ratio of catalyst to ligand of 1:2,using L3 as the ligand in the catalytic system,high-quality poly（octyl-3-thiophenecarboxylate）can be obtained,with an average molecular weight of up to 80.3 k Da（PDI=1.71）,and a regioregularity and yield exceeding 90%.2)Construction of catalytic system involving nitrogen containing ligands and preparation of ester substituted polythiophene by direct C-H/C-H coupling polycondensation.Four nitrogen-containing compounds,4’-phenyl-2,2’:6’,2’-tribipyridine（T1）,4’-（p-toluene）-2,2’:6’,2’-bipyridine（T2）,4-（[2,2’:6’,2’’-bipyridine]-4’-yl）-N,N-dimethylaniline（T3）and4-（[2,2’:6’,2’’-bipyridine]-4’-yl）phenol（T4）,were added as tridentate ligands,respectively,with Pd（OAc）₂ as catalyst and Ag₂CO₃ as oxidant,KOAc is the base of the catalytic system.The effects of different ligands and catalyst/ligand ratios on the direct C-H/C-H coupling polycondensation reaction of octyl-3-thiophenecarboxylate were systematically studied.The research results show that the addition of nitrogen containing ligands significantly improves the efficiency of the condensation reaction.Under the condition of a catalyst to ligand molar ratio of 1:2,using T3 as the ligand in the catalytic system,high molecular weight poly（octyl-3-thiophenecarboxylate）can be obtained,with a maximum average molecular weight of 92.6 k Da（PDI=2.37）,a maximum yield of 84%,and a regioregularity of about 62%.3)Synthesis of ester substituted polythiophene by microwave assisted direct C-H/C-H coupling polycondensation.The direct C-H/C-H coupling polycondensation reaction of octyl-3-thiophenecarboxylate（M）was studied,and the effects of microwave reaction mode,microwave power,reaction temperature,reaction time,solvent,and monomer concentration on the polymerization reaction were systematically investigated.The optimal reaction conditions were selected as follows:monomer M（0.3 mmol,1 equivalent,0.1 M）,Herrmann’s catalyst（5 mol%）,oxidant Ag₂CO₃（2 equivalent）,base KOAc（2 equivalent）,DMAc as solvent,Coupling SPS microwave mode,microwave power of 150 W,reaction temperature of 110°C,and reaction time of 1 hour.Under this reaction condition,the polymer yield is 93%,the number average molecular weight is 18.0 k Da（PDI=1.75）,and the regioregularity is77%.This result is comparable to the polymer obtained by conventional oil bath heating for 48 hours.Therefore,using microwave heating can significantly shorten the reaction time of direct C-H/C-H coupling condensation.In addition,we characterized the photoelectric properties of polymers with different regioregularity using UV visible absorption spectroscopy,fluorescence spectroscopy,and electrochemical workstation analysis methods,and evaluated the effect of regioregularity on the photoelectric properties of poly（octyl-3-thiophenecarboxylate）.The research results indicate that as the regioregularity of the polymer increases from78%to 90.2%,the absorption peaks of the solution and thin film states show a slight red shift（solution:red shift from 423 nm to 429 nm;thin film state:red shift from 481nm to 495 nm）,while their fluorescence emission peaks remain unchanged,both located at 570 nm,and the electrochemical band gap of the polymer is around 2.0 e V.