Modular construction of organic materials

This thesis research initiates a systematic approach to the preparation of solid state organic materials. The approach involves organic synthesis, investigation of intermolecular interactions, and physical characterization of materials. Phenylacetylene macrocycles (PAMs) which are made from linear phenylacetylene sequences (PASs) have been chosen to demonstrate this approach.; First, a convergent, stepwise synthesis of PASs was achieved. The methodology allows for complete control over chain length, sequence order, and functional group placement. Chain growth follows nonlinear progression (J. Am. Chem. Soc. 114, 2273(1992)). Upon deprotection of end groups, these PASs are cyclized to phenylacetylene macrocycles (PAMs) in high yield. Control over the ring structure of PAMs is preprogrammed in the synthesis of the precursor PASs. The size of PAM is determined by the length of the sequence, while the geometry and pendant functional groups are governed by co-monomer sequence order (Angew. Chem. Int. Ed. Engl. 31, 922(1992)). Several functional group transformations have been demonstrated which provide an efficient way to modify the side chains of PAMs.; Secondly, self-association of PAMs was studied by variable temperature {dollar}sp1{dollar}H NMR. This self-association was attributed to {dollar}pi{dollar}-stacking interactions of the aromatic rings in PAMs. The strength of this interaction was found to be dependent on the pendant functional groups and the PAM geometry. Electron-withdrawing groups such as esters on PAMs facilitate the {dollar}pi{dollar}-stacking induced self-association, while electron-donating groups such as ethers have just the opposite effect (J. Am. Chem. Soc. 114, 9701(1992)). No evidence was found for the association of PASs. Independently, vapor pressure osmometry (VPO) verified the {dollar}sp1{dollar}H NMR results of the self-association.; Discotic liquid crystals of PAMs have been made and characterized by DSC, X-ray diffraction, and polarized optical microscopy. Design of discotic mesogens was aided by the studies of self-association of PAMs in solution. A discotic nematic phase (N{dollar}sb{lcub}rm d{rcub}){dollar} was found in all the three PAMs studied, while discotic columnar phase with a hexagonal lattice (D{dollar}sb{lcub}rm d{rcub}){dollar} was only found in the PAM with segregated ester and ether functional groups. The single crystal structure of a PAM was determined.