Tunable self-assembly of triazole-linked porphyrin-polymer conjugates

Abstract

The convergence of supramolecular chemistry and polymer science offers many powerful approaches for building functional nanostructures with well-defined dynamic behaviour. Herein we report the efficient "click" synthesis and self-assembly of AB2 - and AB4 -type multitopic porphyrin-polymer conjugates (PPCs). PPCs were prepared using the copper(I)-catalysed azide-alkyne cycloaddition (CuAAC) reaction, and consisted of linear polystyrene, poly(butyl acrylate), or poly(tert-butyl acrylate) arms attached to a zinc(II) porphyrin core via triazole linkages. We exploit the presence of the triazole groups obtained from CuAAC coupling to direct the self-assembly of the PPCs into short oligomers (2-6 units in length) via intermolecular porphyrinatozinc-triazole coordination. By altering the length and grafting density of the polymer arms, we demonstrate that the association constant of the porphyrinatozinc-triazole complex can be systematically tuned over two orders of magnitude. Self-assembly of the PPCs also resulted in a 6 K increase in the glass transition temperature of the bulk material compared to a non-assembling PPC. The modular synthesis and tunable self-assembly of the triazole-linked PPCs thus represents a powerful supramolecular platform for building functional nanostructured materials.

Keywords: click chemistry; cycloaddition; polymerization; porphyrins; supramolecular chemistry.