Foldamers from crowded aromatics; New pentacene and tetracene derivatives for molecular electronics

This thesis discusses five sections, spanning two fields, all linked intellectually. Functional organic molecules are proposed, synthesized and their supramolecular structure is elucidated and electronic properties are studied.;Part I. Foldamers. A general method is developed to synthesize a new class of folded oligomers from crowded aromatics. Unlike most foldamers, each subunit of these oligomers is highly substituted and functional. Moreover, this new folded motif, formed through a synergy between hydrogen bonds and pi-stacking, is so robust that even dimers have secondary structures in solution. Results from dimers and a trimer indicate that rigidifying linkers and unhindered side chains are the two critical ingredients to produce a stable columnar secondary structure from these oligomers.;A hexamer from crowded aromatics, due to its longer dimension, is desired for biological applications. Such a hexamer is synthesized and has shown to fold into secondary structure in dichloromethane by site-selective fluorescence spectroscopy. In dichloromethane, unfolding of the hexamer occurs upon heating or addition of methanol. Titration experiments indicate a cooperative folding of the hexamer in dichloromethane. The free energy difference between the folded and the unfolded states is estimated to be --2.0 kcal mol -1.;Part II. Acenes. This section involves acenes, functionalized for desired electronic properties and other applications.;A stable pentacene derivative containing long ether chains is prepared in 6 steps. It can be simply drop-cast onto silicon wafers to make organic field-effect transistors (OFETs). A top-contact single-wire device shows a field-effect mobility of 1.4 x 10-2 cm2 V-1 s-1 and an on/off current ratio of 3 x 103. Bottom-contact devices have repeatable photoresponse. The crystal structure of this derivative shows a co-facial packing and the charge carrier transport is likely through the alkynyl bonds sandwiched between aromatic rings.;2,3,9,10-Tetrakis(trifluoromethyl)pentacene is synthesized in 11 steps. This compound is soluble in a variety of solvents and relatively stable in solution. It adopts co-facial stacking in single crystals.;A facile route to tetracene derivatives with 2,3-dicarbonyl substituents is put forth. N-Phenyl-2,3-tetracenedicarboximide is prepared by condensation of anthracene-2,3-dialdehyde and N-phenylmaleimide. Functional group transformations and simple purifications give the tetracene bisamide, diacid, anhydride, dicarboximide and alkyl dicarboximide. These compounds, bearing both a tetracene moiety and functional groups, may be useful in OFETs, chiral fluorescent labeling or molecular recognition.