Connective CC Double Bond Formation for the Synthesis of Donor- and Acceptor-Substituted Poly(<i>p</i>-phenylenevinylene)s

Abstract

A carbon−carbon bond formation through cation−anion coupling allows the synthesis of poly(p-phenylenevinylene)s (PPV) 1 and 2a−f, which contain donor and acceptor groups in each vinylene unit. The crucial step in the double bond formation is the quantitative elimination of methanethiol at room temperature. In this work we describe the optimization of the molecular weight of polymers of structure types 1 and 2a−f with regard to (i) solubility of the monomers and polymers and (ii) the reactivity and side reactions of the monomers. The simultaneous donor and acceptor substitution on the central double bond in PPV-analogous structures raises the question of the additivity of dipoles in each repeat unit of a conjugated polymer chain from the viewpoint of potential use in electrooptical applications. The sequence of donor and acceptor groups along the π-conjugated chain can be controlled by the choice of suitable monomers and is crucial for the alignment of the dipole components. The aggregation of polymers 1 and 2a−f, observed in the GPC, makes it necessary to introduce MALDI-TOF mass spectrometry for the determination of the molecular weight of the donor- and acceptor-substituted polymers. The thermal properties are determined with regard to the high-temperature stability demanded for use in nonlinear optics (NLO).