Synthesis of Long-Chain Oligomeric Donor and Acceptors via Direct Arylation for Organic Solar Cells

The rapid synthesis of structurally complicated electron donors&acceptors still remains a major challenge in organic solar cells(OSC).In this work,we developed a highly efficient strategy to access long-chain oligomeric donor and acceptors for OSC applications.A series of cyclopentadithiophene(CPDT)and benzothiadiazole(BT)-basedπ-conjugated oligomers,i.e.,three oligomeric acceptors(BTDT)n-IC(n=1—3)and one long-chain oligomeric donor(BTDT)4-RD,are facilely synthesized by an atom-and step-economical,and labor-saving direct C—H arylation(DACH)reaction(i.e.,C—H/C—Br cross coupling).Note that(BTDT)4-RD involving five CPDT,four BT and two rhodamine(RD)building blocks is the longest oligomeric donor in the fullerene-free OSC devices ever reported.The dependence of the structure-property-performance correlation of(BTDT)n-IC(n=1—3)and(BTDT)4-RD on theπ-conjugation lengths is thoroughly investigated by opto-electrochemical measurements,bulk heterojunction(BHJ)OSC devices and microscopies.The(BTDT)1-IC:PBDB-T and(BTDT)4-RD:Y6 BHJs achieve power conversion efficiencies of 9.14%and 4.51%,respectively.Our findings demonstrate that DACH reaction is a powerful tool to tune the opto-electronic properties and device performances by regulating the lengths ofπ-conjugated oligomers with varied numbers of repeating units.

Thienylmethylene Oxindole Based Conjugated Polymers via Direct Arylation Polymerization and Their Electrochromic Properties

Direct arylation methods have been used to polymerize thienylmethylene oxindoles(TEIs)and 3,3-bis[[(2-ethylhexyl)oxy]methyl]-3,4-dihydro-2 H-thieno-[3,4-b][1,4]dioxepin(ProDOT)for new donor-acceptor conjugated polymers.The polymers exhibited blue hues in neutralstate with distinct color-to-transmissive reversible electrochromic switching under applied potentials from 0 V to+1.5 V,and showed high coloration efficiencies(436-438 cm^(2)·C^(-1))in near-infrared regions with high switching speeds around 1-2 s under ambient conditions.

Synthesis of Thieno[3,4-b]pyrazine-based Alternating Conjugated Polymers via Direct Arylation for Near-infrared OLED Applications

Three alternating conjugated polymers,namely PFTP,PCz TP,and PSi TP,which combine a thieno[3,4-b]pyrazine(TP)unit with different benzene-based donor units such as 9,9-dioctylfluorene,9-heptadecyl-9H-carbazole and 5,5-dioctyl-5H-dibenzo[b,d]silole,were synthesized in good yield(>85%)and high molecular weight up to Mn=5.82×10^(4) via direct arylation polymerization(DAr P).All the resultant polymers exhibit moderate bandgap of about 1.80 e V and strong deep red/near-infrared emitting in the solid state.Among them,the PSi TP-based electroluminescence(EL)devices with an architecture of ITO/PEDOT:PSS/PTAA/emitting layer/TPBi/Li F/Al give the best performance with a maximum luminance of 2543 cd/m^(2) at 478 m A/cm^(2).This work expands the application scope of high-performance conjugated polymers which can be synthesized by DAr P.

Substituent Effects on Direct Arylation Polycondensation and Optical Properties of Alternating Fluorene-Thiophene Copolymers

Four thiophene derivatives were prepared by replacing the 3,4 positions of thiophene by―OCH3, ―CH3―COOCH3 and ―CN, respectively. The polycondensations via direct arylation took place between the four thiophene derivatives and 2,7-dibromo-9,9-dioctylfluorene under six various catalytic conditions to investigate the substituent effects. The substituent can affect the electron cloud density of the active C―H bond, which can be monitored by the NMR chemical shift. The experimental results show that the reactivity decreases with increasing the chemical shift of active C―H bonds in the four thiophene derivatives, and thus can promote the direct arylation polycondensation. This phenomenon is explained by the electrophilic aromatic substitution（SEAr） mechanism. UV-Visible absorption and photoluminescence were studied to investigate the substituent effect on optical properties of the four copolymers. The results show that these alternating fluorene-thiophene copolymers with different substituents are good fluorescent materials and promising in PLED applications.

Direct Arylation Polycondensation of Thiophene-Based C−H Monomers

Direct arylation polycondensation(DArP)has emerged as an eco-friendly and atom-efficient methodology for the syntheses ofπ-conjugated polymers(CPs).This approach features the direct C—H arylation of an aromatic hydrocarbon with an aryl halide.Given the prevalence of thiophene-containing CPs,achieving efficient and defect-free DArP of thiophene-based C−H monomers is of great significance.This review presents a mechanistic insight into DArP and describes the development of DArP catalytic systems for varied thiophene-based C−H monomers.Moreover,the control of the primary defects(i.e.,branching and homo-coupling)in thiophene-based DArP is also elaborated.By emphasizing the principles behind monomer selection and catalytic system optimization,this review intends to provide a framework for future advancements in the DArP of thiophene-containing CPs.

3-Methylcyclohexanone Processed n-Channel Organic Thin-Film Transistors Based on a Conjugated Polymer Synthesized by Direct Arylation Polycondensation

The solubility of a direct arylation polycondensation(DArP)synthesized conjugated polymer,i.e.,poly(3,6-bis(furan-2-yl)-2,5-bis(4-tetradecyloctadecyl)-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-1,2-bis(3,4-d ifl uorothien-2-yl)ethene)(PFuD PP-4FTVT),in variou s organic solvents was studied.The polymer is soluble in 3-methylcyclohexanone(3-MC),a green solvent from peppermint oil,besides other solvents such as anisole,cyclopentyl methyl ether(CPME)and o-dichlorobenzene(o-DCB),etc.Based on the Hansen solu bility parameters(HSP)analysis,3-MC is identified as a"marginal solvent"of PFuDPP-4FTVT.The morphology of the spin-coated films with 3-MC as the solvent strongly correlated with the solution preparation conditions.With a 3-MC solution aged for 3 h at 70℃,n-channel organic thin-film transistors(OTFTs)with electron mobility(μe)above 1 cm^(2)·V^(-1)·s^(-1) and current on/off ratio(Ion/Ioff)higher than 105 were fabricated by spin-coating.This is the first report on high mobility conjugated polymers for OTFTs processible with natu rally occurred green solvent.

Facile and Cost-Efficient Synthesis of Photovoltaic Polymers via Direct Arylation Coupling

As the high calibre candidate of lightweight and flexible solar cells,polymer solar cells(PSCs)have made tremendous progress in recent years.However,the active photovoltaic materials in PSCs are mainly synthesized by metal-mediated coupling reaction requiring harsh reaction conditions,multiple-step synthesis,and cumbersome purification,which is not cost-efficient and may bring toxicity concerns.It is not favorable to the production of photovoltaic polymers and PSC devices on a large scale,and therefore unsuitable for the PSCs industrialization.Direct arylation coupling reaction via aromatic C―H bonds activation enables the synthesis of conjugated polymers under mild conditions and simultaneously reduces synthetic steps,difficulty,and toxic reaction byproducts.This review provides an overview of the history of preparing representative photovoltaic polymers utilized in PSCs through direct arylation reactions and discusses the activity and selectivity of C―H bonds in typical building blocks under different reaction conditions.Especially,the impact of direct arylation condition on defect formation and photovoltaic performance of the photovoltaic polymers is addressed and compared with conventional Stille coupling methods.

Direct Arylation of Substituted Pyridines with Arylboronic Acids Catalyzed by Iron(Ⅱ) Oxalate

The direct arylation of substituted pyridines with several arylboronic acids has been developed.This transformation could proceed readily at ambient temperature using inexpensive reagents:iron(Ⅱ)oxalate as a catalyst,potassium persulfate as a co-oxidant,which can afford the arylated products in mild to good yields.The mechanism is presumed to proceed through a nucleophilic radical addition to the pyridines with in situ reoxidation.

One-Pot Synthesis of 3-to 15-Mer π-Conjugated Discrete Oligomers with Widely Tunable Optical Properties

Main observation and conclusion A series of all-donor type alternating(D1-D2)monodisperse oligomers based on cyclopentadithiophene(CPDT)and 1,4-difluoro-benzene(DFB)with gradually increasing chain lengths containing 3 to 15 monomers were successfully synthesized via one-pot C-H direct arylation reaction.As confirmed by various structural characterizations,all these long-chain oligomers are monodispersed with defined structures.The length-dependent optical and electrochemical properties with the evolution from the shortest oligomer(01)to the longest oligomer(07)and their parent polymer P1 have been studied in details.By simply tuning the mixing ratio of discrete oligomers,the photoluminescence(PL)in a wide range of color emissions extending to near-white can be facilely modulated,ilus-trating the potential of these monodisperse conjugated oligomers for light emission application.The atom-,step-and pot-economic synthetic strategy here developed will open the door toward efficient and controllable synthesis ofπ-conjugated oligomers for accu-rate structure-property relationship study and optic&electronic device applications.