Various cyclohexyl end-capped oligomeric semiconductors based on oligothiophene, oligothiophene-fluorene, and perylene diimide have been synthesized using Stille and Suzuki coupling. These materials exhibit increased solubility over their unsubstituted and hexyl-substituted counterparts and have been successfully employed as the active component in organic field-effect transistors. The morphology of vacuum-deposited films made with these oligomers has been investigated using atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Field effect mobility as high as 0.17 cm 2/V·s was observed in fluorene-thiophene oligomers deposited at elevated substrate temperatures. With the series of materials, a correlation between the size of the endgroup with respect to the size of the inner semiconducting core of the molecule is found to be an important factor in orienting the molecules with their long axis perpendicular to the substrate surface in the thin film phase, and directly related to charge transport in these materials.
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