| Several oligothiophene derivatives have been synthesized for use as the semiconducting layer in p- and n-type thin-film transistors. A series of quinoid oligothiophene molecules has been synthesized and characterized by UV-visible spectroscopy, mass spectrometry, cyclic voltammetry (CV), X-ray crystallography, and NMR spectroscopy. These molecules are electronically equivalent to a two-electron oxidized aromatic oligothiophene, and exhibit reversible oxidations and facile reductions on the CV timescale, indicating their potential for use as n-type (and possibly ambipolar) materials. A subset of these quinoidal compounds was further investigated with a variable-temperature 1H NMR study, which shows they undergo conformational isomerization on the NMR timescale in solution at relatively low temperatures. Kinetic parameters for a particular quinoid oligothiophene, 5,5"-bis(dicyanomethylene)-3,3',3"-trihexyl-5,5"dihydro-2,2':5',2"-terthiophene, were obtained via linefitting from these variable-temperature 1H NMR data.; A series of tricyanovinyl-capped oligothiophenes is also reported. These molecules behave as n-type materials, and display very different electronic properties relative to their unsubstituted analogues; the tricyanovinyl group can function as an internal electron acceptor, which significantly decreases the HOMO-LUMO energy gap. 3,3"'-Dihexyl-5-(tricyanovinyl)-2,2':5',2":5",2"'-quaterthiophene was further investigated by X-ray crystallography, theoretical analysis, and infrared spectroelectrochemistry. These experiments indicate that injected electrons are localized on the tricyanovinyl group, which provides insight into the mechanisms of electron transport in the crystalline solid.; Naphthalene capping groups were used to create another series of substituted oligothiophenes. Vacuum sublimation was used to grow X-ray quality crystals of several of these compounds, which exhibit edge-to-face packing motifs in the solid state. These compounds exhibit reversible oxidations on the CV timescale, indicating their suitability as candidates for p-type semiconductor materials. The electronic properties of these molecules can be tuned by altering the number of thiophene rings in the oligomers, and their solubilities can be adjusted by the incorporation of ancillary alkyl chains. Initial device testing results indicate these molecules exhibit favorable p-type properties. A pyrene-capped compound, 5,5'-bis(2-pyrenyl)-2,2'-bithiophene, was synthesized and found to exhibit both edge-to-face and pi-dimer interactions in the crystalline solid. Initial results indicate this molecule exhibits good p-type semiconductor properties. |
