Synthesis and Electrochemistry of Molecular Dumbbells. Triblock Copolymers of Dendrons and Rigid Rods

Abstract

Polyether dendrons, generations 1−4, were connected to naphthalene diimides and rigid rod naphthalene diimide-benzidine oligomers. This provided a series of well-defined triblock copolymers with flexible dendrons on both ends of rigid rods. The largest of these used generation-4 dendrons with a 4.4-nm rigid rod containing two diimides and three benzidines. The estimated length of this molecule is 10 nm. Electrochemical reduction in DMF provided anion radicals on each diimide of the rigid rod. The diffusion coefficients and rates of these reductions were measured using cyclic voltammetry. The diffusion coefficients were successfully compared with predictions for diffusing prolate ellipsoids. Comparison of the heterogeneous rate constants showed that larger dendrons slowed the electrochemical reaction, and had slightly larger effects when the rod was shorter. It is proposed that the bulky dendrons prevent access of the diimide groups to the electrode even when they are not directly connected to the diimide....