Molecular Ordering of Dithieno[2,3-;2',3'-]benzo[2,1-:3,4-']dithiophenes for Field-Effect Transistors.

Four derivatives of dithieno[2,3-;2',3'-']benzo[1,2-;3,4-']dithiophene () have been synthesized to investigate the correlation between molecular structure, thin-film organization, and charge-carrier transport. Phenyl or thiophene end-capped derivatives at alpha positions of the outer thiophenes of present vastly different optoelectronic properties in comparison with bay-position alkyl-chain-substituted , which was additionally confirmed by density functional theory simulations. The film morphology of the derivatives strongly depends on alkyl substituents, aromatic end-caps, and substrate temperature. Field-effect transistors based on derivatives with bay-substituted alkyl chains show the best performance within this studied series with a hole mobility up to 0.75 cm/V s. Attachment of aromatic end-caps disturbs the ordering, limiting the charge-carrier transport. Higher substrate temperature during deposition of the derivatives with aromatic end-caps results in larger domains and improved the transistor mobilities but not beyond the alkylated .