Synthesis and Properties of [3]Rotaxanes with Two Oligo(para-phenylene) Axles.

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Oligo(para-phenylene) (PPn) is a π-conjugated compound where phenylene units are directly connected at the 1,4-positions. Utilizing the catalytic activity of the macrocyclic dihydrodibenzophenanthroline-Ni complex, we succeeded in the synthesis of [3]- and [2]rotaxanes with PPn axles by biaryl coupling. The size of the macrocycle was critical to synthesize [3]rotaxanes, which consist of two oligo(para-phenylene) axles, in good yields. The relationship between the length of the PPn structure on the 1H NMR spectra of the rotaxanes was studied. The aggregation of a PP8 derivative was suppressed by the presence of the macrocycle in the rotaxanes. A [3]rotaxane could be considered as a model compound of an aggregated PPn, and the photophysical studies disclosed the influence of the aggregation on the properties of PPn.