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McBee, Ian

Chemistry

2007

MS

A wide variety of arylene-ethynylene macrocycles have been synthesized following the production of tribenzohexadehydro[12]annulene in 1966. Their aromatic backbones and shape-persistent cavities have been employed for a variety of applications, such as liquid crystals, anisotropic solids, or metal complexation. A p-terphenylene-ethynylene macrocycle was synthesized via sequential Suzuki-Miyaura couplings to assemble the p-terphenylene monomer, followed by Sonogashira cyclooligomerization to afford the cyclotrimer, which proved to be highly insoluble and inseparable from the reaction side products. Making use of orthogonal protection and a split-pool strategy, the linear trimer was assembled in a stepwise manner, followed by ring-closing Sonogashira coupling to selectively produce the cyclotrimer. To aid in solubilizing the cyclotrimer, a monomer was synthesized with an n-octyl substitution. Upon Sonogashira cyclooligomerization, both the cyclotrimer and the cyclodimer were produced and isolated, and found to be significantly more soluble in common organic solvents than the unsubsituted cyclotrimer. All three macrocycles were found to be blue fluorophores with moderate Stokes shifts. The unsubstituted cyclotrimer exhibited an unusual hypsochromic shift in the excitation spectrum upon a change in solvent. All three macrocycles were also found to absorb at shorter wavelength than would be expected for a fully-conjugated system, which is indicative of a break in conjugation caused by the free rotation of the p-phenylene moieties.