Ring-opening Of Dithieno[2,3-b:3’,2’-d]thiophene And The Improved Synthesis Of Dithieno[3,2-b:3’,4’-d]thiophene

Fused thiophenes have been applied in the fields of organic field effecttransistors （OFETs）, organic light emitting diodes （OLEDs） and organic solar cells（OSCs） due to their promising optical and electrical properties. Hence the chemistrystability of fused thiophenens in organic chemistry seems to be very important in boththeory and application. Our group have firstly investigated the ring-opening reactionof dithieno[2,3-b:3’,2’-d]thiophene and its derivatives in the presence of n-BuLi. Inthis paper, further work about the ring-opening reaction was studied in the presence ofdifferent aryllithiums. By the ring-opening reaction of dithieno[2,3-b:3’,2’–d]thiophene with aryllithiums, four kinds of unusual arylsulfanyl substitutedquarterthiophene were generated. We also investigated the photophysical properties ofthe four compounds. In addition, another isomeric dithienothiophene,dithieno[3,4-b:3’,4’-d]thiophene, was synthesized through an improved method. Thiswork includes three parts as following:（1） With nine bromo-substituted aromatic compounds, nine aryllithiums weregenerated in situ. Nine ring-opening products[2’-phenylsulfanyl-5,5’-dioctyl-[3,3’]-bithiophenyl-2-carbaldehyde（7）,2’-（4-methylphenylsulfanyl）-5,5’-dioctyl [3,3’]bi-thio phenyl-2-carbaldehyde（8）,2’-（4-methoxylphenylsulfanyl）-5,5’-dioctyl-[3,3’]bi-thiophenyl-2-carbaldehyde（9）,2’-（4-cyanolphenylsulfanyl）-5,5’-dioctyl-[3,3’]bithiophenyl-2-carbaldehyde（10）,2’-[4-（N,N-dimethylamino）-phenylsulfanyl]-5,5’-dioctyl-[3,3’]bithiophenyl-2-carbaldehyde（11）,2’-（1-naphthylsulfanyl）-5,5’-dioctyl-[3,3’]bithiophenyl-2-carbaldehyde（13）,2’-（9-anthrylsulfanyl）-5,5’-dioctyl-[3,3’]bithiophen-yl-2-carbaldehyde（14）,2’-[4-（N,N-diphenylamino）-phenylsulfanyl]-5,5’-dioctyl [3,3’]-bithiophenyl-2-carbaldehyde（15）,2’-（1-pyrenylsulfanyl）-5,5’-doctyl[3,3’]bithiophen-yl-2-carbaldehyde]（16） were produced by the ring-opening of2,5-dioctyldithieno-[2,3-b:3’,2’-d]thiophene with nine arylithiums. Yields of these reactions were from42%to88%. The yields indicated that strong nucleophilicity of the aryllithiumreagents can intensify the efficiency of ring-opening. The steric effect is another factorthat could influence the yield. As the steric hindrance become stronger, the efficiencyof of ring-opening became lower. All the products were characterized by¹H NMR, ¹³C NMR and HRMS. The structure of2’-（1-pyrenylsulfanyl）-5,5’-dioctyl [3,3’]bithiophenyl-2-carbaldehyde （16） was confirmed by crystal structure.（2） Utilizing the ring-opening reaction,2,5-bis-（4-trimethylsilyl）-thiophene[2,3-b:3’,2’-d]thiophene were reacted with9-anthryllithium and1-pyrenelithium respectively.Pyrenylsulfanyl substituted and anthrylsulfanyl substituted oligothiophenes weregenerated （20,21）. After the removal of TMS protecting group, two anotherarylthio-substituted oligothiophene were generated （22,23）. These four compoundswere not easy to be produced by usual methods. Absorbance and fluorescencespectrum of these four compounds （20,21,22, and23） were tested. Compounds20and22showed strong fluorescence-emissions in chloroform, as the concentration ofthe compounds increased from10-7M to10-3M, the fluorescence-emissions increasefirstly then decrease. When compared to the fluorescence-emissions of compound25,there was a new emission peak of compound22at the area of480nm to500nm. Wepresumed that compound22may contain intermolecular excimers. When thesecompounds were in the solvent which water and THF were mixed, as the proportionof water getting to a certain percentage （70%）, the fluorescence of substancesdramatically increased. Aggregation effects were found in two compounds （20,22）.（3） With3,4-dibromothiophene as starting material,dithieno[3,4-b:2’,3’-d]thiophene with TMS group （28） was generated with theimproved yield of50%compared with10%reported by literature. The improvedsynthetic route including with four steps: TMS protection, disulfidation, reaction with1-TMS-3-Bromothiophene, coupling by copper chloride. All compounds wereconfirmed by¹H NMR,¹³C NMR, and HRMS.