Controlling the Orientation of Pendants in Two-Dimensional Comb-Like Polymers by Varying Stiffness of Polymeric Backbones

Abstract

The electronic communications between chromophores are closely related to distances and orientation of these π-conjugated systems. Reported herein is a collection of well-defined two-dimensional comb-like polymers containing porphyrin pendants obtained by ring-opening metathesis polymerizations of norbornene and cyclobutene derivatives using ruthenium or molybdenum catalysts. The spacing separating the adjacent pendants are defined by ring sizes of cycloalkenes and the orientations are determined by the stiffness of the polymeric backbone, which is, in turn, discerned by the percentage of <i>Z</i>-double bonds. Both peak widths of the porphyrin radical cation of the EPR spectra and the absorption profiles in the Soret band region reflect the degree of the spin delocalization and exciton coupling between porphyrin pendants in these polymers and, hence, the stiffness of the polymeric backbone. Our approach offers a useful protocol to align an array of chromophores appended onto a rigid polymeric backbone so that the optoelectronic properties can be tuned