Complexation of Poly(phenylenevinylene) Precursors and Monomers by Cucurbituril Hosts

Abstract

The formation of highly stable inclusion complexes between the host cucurbit [7]uril (CB7) and the dicationic guests bis(diethylsulfonium)-p-xylylene (12+) and bis(tetrahydrothiophenium)-p-xylylene (22+) was demonstrated by mass spectrometric, NMR and UV−vis spectroscopic data. Although the inclusion complexes did not undergo Wessling polymerization, the monomers can be pre-polymerized to the polyelectrolyte stage and subsequently exposed to CB7 in aqueous solution. The CB7-treated polyelectrolyte developed conjugation more readily and at much lower temperatures than the untreated polyelectrolyte to yield poly(phenylenevinylene) (PPV). The formation of external complexes between CB7 and the cationic branches of the polyelectrolyte favored the cleavage of the branches. CB7 was also found to form a stable complex with diethyl sulfide (Et2S), the product of the elimination reaction that converts the polyelectrolyte to PPV. In contrast, the smaller analogue, the cucurbit [6]uril host (CB6) did not have any effect on the polyelectrolyte-to-PPV conversion. The CB7-treated polyelectrolyte showed enhanced luminescence both in solution and in precursor polymer films. Et2S@CB7 inclusion complexes located around the polymer chains seem to form a hydrophobic shell, which effectively protects the PPV chains from quenchers, such as vapor-phase dinitrotoluene molecules.