Synthesis and properties of a benzo[1,2-b:4,5-b ']dithiophene core pi-system that bears alkyl, alkylthio and alkoxy groups at 3,7-positions

A synthetic sequence was developed to provide 3,7-didodecylbenzo[1,2-b:4,5-b']dithiophene and its dialkylthio and dialkoxy analogues as planar and soluble building-blocks for constructing benzodithiophene-based pi-systems. The benzodithiophenes were also transformed to the corresponding 2,6-di(5-phenyl-2-thienyl)-capped derivatives as the representative oligomers. Their absorption and emission spectra as well as CV data showed that the HOMO-LUMO energy gaps of the dialkylthio and dialkoxy derivatives are smaller than that of the dialkyl one, which is attributable to the lower E-LUMO as well as E-HOMO energies of the dialkylthio analogue and the higher E-HOMO energy of the dialkoxy analogue, respectively. The intra- and intermolecular charge-carrier mobilities were then estimated by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) method and solution-processed top contact FET performance. The TRMC method showed similar high intrinsic hole mobilities (0.16-0.24 cm(2) V-1 s(-1)) irrespective of the substituents, whereas the dialkyl derivative especially displayed a good field-effect mobility of 0.023 cm(2) V-1 s(-1).