HIGHLY UNSATURATED OLIGOMERIC HYDROCARBONS - ALPHA-(PHENYLETHYNYL)-OMEGA-PHENYLPOLY[1,2-PHENYLENE(2,1-ETHYNEDIYL)]

A new set of conjugated oligomers C6H5C=C-(1.2-C6H4C=C)n-C6H5 (10; n=37) comprised of acetylene and phenyl units linked together at the 1,2 positions of the aromatic ring is introduced. The facile synthesis of these compounds is achieved through the Pd-mediated coupling reaction of diiodo- and dibromobenzene with the appropriate ethynyl component. Spectroscopic data of the new compounds are discussed in light of electronic conjugation of the extended pi system. Thermolysis of oligomers 10 indicates that rearrangement of the triple bonds occurs to form higher conjugated oligo(acenes). The topology of two members (10; n=2, 3) is confirmed by X-ray analysis and reveals a propensity for intramolecular pi-stacking of the phenyl rings leading to a helical arrangement.