Creating new building blocks for organic electronics: Synthesis, assembly and devices

Described in this thesis are studies to apply methods of organic synthesis and motifs from supramolecular chemistry to design and create new building blocks for organic electronics, emphasizing on their applications in organic thin film transistors. Chapter 2 demonstrates controlled stacking of sulfur-substituted benzenes through hydrogen bonds. The resulting columnar structure can be directed with electric fields. In Chapter 3, electrostatic interactions are introduced to mediate molecular packing of organic semiconductors. A general route is developed to synthesize end-functionalized linear acenes. The synthesis, crystal structures and field effect transistors of linear acenes substituted with F, O and N atoms are illustrated. The relationship between molecular structure and assembly is emphasized. Chapter 4 describes dihydrodiazapentacene as an isostructural motif for pentacene and details its synthesis, assembly and thin film transistors. Chapter 5 discusses how to attach organic semiconductors to gate oxides to approach in situ assembly of monolayer field effect transistors. This method gives high yields of working devices that have source-drain distances less than 100 nm and provides a new avenue for research in thin-film organic transistors where the active molecules are linked to the dielectric surface. In Chapter 6, sterically encumbered aryl groups are applied to block the herringbone motif that is typical of many acenes and direct the arrangement of pentacene backbones into higher-order structures. Analyzing the crystal structures of a series of cruciform shaped pentacenes allows better understanding the relationship between molecular structure, assembly and properties. Field effect mobility up to 0.1 cm2/V•s has been obtained from the thin films that lack long-range order.