Synthesis And Photocatalytic Application Of Thiophenopyrrolidone Based Conjugated Polymers

Green energy is the key to realizing"carbon peaking"and"carbon neutrality".Hydrogen energy,as a clean and renewable energy source,has drawn widespread concern due to its advantages,such as high energy density,zero carbon emissions and environmental pollution-free.Visible-light driven water splitting for hydrogen production is one of the most dominant hydrogen production methods.Among many photocatalysts,conjugated polymers are considered to be the most promising materials for photocatalytic hydrogen production due to their flexible design,diverse synthesis methods and tunable band gaps.Conjugated polymers are mainly synthesized by C-C coupling polymerization.Among these polymerization methods,Stille and Suzuki coupling have been able to synthesize diverse conjugated polymers,but there exist imperfections,such as difficulties in pre-functionalization and purification of monomers,many synthesis steps,and toxic and harmful by-products and so on.Direct C-H/C-H coupling reaction has the advantages of easy availability of monomer,no prefunctionalization,high atom economy and no end capping in post treatment,which is more in line with the development concept of green chemistry.In this paper,a series of thienopyrrolidione based conjugated polymer were constructed by direct C-H/C-H coupling polymerization reaction with an atom-economic and eco-friendly way,and nanoparticles were prepared by nano precipitation method.The relationship between material structure and its optical and electrical properties was systematically studied,and its photocatalytic performance was examined.Details of the research are as follows:1.Synthesis of thienopyrrolidione based conjugated polymers.Conjugated polymers P1 and P2 were synthesized by direct C-H/C-H cross-coupling polymerization with 5-（2-octyl-1-dodecyl）-4H-thienol[3,4-c]pyrrolo-4,6（5H）-dione as monomer and 3,3’-dioctyl-2,2’-bithiophene,4,4-dioctyl-cyclopentane[2,1-b:3,4-b]dithiophene,respectively.Taking the direct C-H/C-H cross-coupling polymerization of P1 as an example,reaction conditions such as palladium catalyst,phosphine ligand,temperature and solvent were screened.The optimal polymerization reaction conditions were as follows:Pd（PPh₃）₄ as catalyst,P（t-Bu）₂Me HBF₄ as ligand,Ag₂CO₃ as oxidant,KOAc as additive,and DMAc:Xylene（v/v=1:1）as solvent in 80°C for 48 h.The structure and molecular weight of P1 and P2 were determined by NMR and GPC.The UV-vis absorption spectrum shows that the absorption of P1 and P2 is in the visible light region.The electrochemical analysis shows that the E_g^cv of P1 and P2 are 2.25 e V and 2.49 e V,respectively.Thermogravimetric analysis shows that P1 and P2 have high thermal stability.The spectral,band gap and stability of P1 and P2 meet the requirements for the photocatalytic decomposition of water to produce hydrogen.2.Study on photocatalytic performance of thienopyrrolidione based conjugated polymer nanoparticles.Nanoparticles P1-NPs and P2-NPs were prepared from P1 and P2 by nano-precipitation method.The photocatalytic hydrogen production of P1-NPs and P2-NPs was studied by using ascorbic acid as electron sacrificial agent under simulated sunlight without other cocatalysts.The hydrogen production tests of P1-NPs and P2-NPs at different concentrations show that the highest hydrogen production rate of P1-NPs is 101.38μmol h^-1·g^-1 at 0.05 mg/m L.the highest hydrogen production rate of P2-NPs is 289.16μmol h^-1·g^-1 at 0.15 mg/m L.In addition,the photocatalytic hydrogen production rate of P2-NPs is higher than that of P1-NPs at the same concentration,which is mainly due to the cyclopentane[2,1-b:3,4-b]dithiophene structure of P2,increasing the planeness of the main chain of conjugated polymer.The better the planeness,the more favorable for photocatalytic hydrogen production.3.Synthesis and photocatalytic properties of conjugated polymers with alkoxy side chain.5-（2-octyl-1-dodecyl）-4H-thienol[3,4-c]pyrrolo-4,6（5H）-dione was used as monomer,P3 and P4 were synthesized by direct C-H/C-H cross-coupling polymerization with 4,8-bis（octyloxy）benzo[1,2-b:4,5-b]dithiophene and 3,4-vinyl dioxythiophene,respectively.The structures of P3 and P4 were identified by NMR.Both P3 and P4 has strong absorption in the visible region,high thermal stability,and suitable electrochemical band gap（>1.23 e V）,which meets the basic requirements of photocatalytic produce hydrogen.P3-NPs and P4-NPs were prepared by nano precipitation method,and ascorbic acid were added to test their photocatalytic hydrogen production performance under simulated sunlight.The results show that P3-NPs exhibit the highest HER performance of 1819.35μmol h^-1·g^-1 and 6090.40μmol h^-1·g^-1 in the absence and presence of Pt co-catalyst,indicating that the alkoxy side chain achieves the dual effect of hydrophilicity and binding with the co-catalyst,which is conducive to improving the hydrogen production performance of the organic photocatalyst.