Synthesis and optical properties of poly(2,11-triphenyleneethynylene-alt-m-phenyleneethynylene)s

Triphenylene units are introduced into the backbone of a poly(m-phenyleneethynylene) (mPE). The new polymer, mPPET, exhibits strong intra-chain folding in good solvents in which the polymer is soluble, such as chloroform, benzene, and THF. In poor solvents, where the polymer is insoluble, such as acetonitrile, hexane, or DMSO, interchain aggregation dominates. In a solvent mixture of a good solvent and a poor solvent with appropriate ratios, mPPET appears to adopt a random coil conformation. Among the three conformations (intra-chain folding, interchain aggregation, and random coil chain), the intra-chain polymeric foldamer exhibits the highest fluorescence quantum yield. These results indicate that introducing a planar polynuclear aromatic compound into mPE not only increases its intra-chain folding propensity, but also may enhance its fluorescent properties. This approach may be applied to synthesize a variety of conjugated foldamers containing planar polynuclear aromatic hydrocarbons with interesting photophysical properties.