Aqueous Self-Assembly of an Electroluminescent Double-Helical Metallopolymer

Abstract

A new type of water-soluble copper-containing polymer has been synthesized using the technique of subcomponent self-assembly. Copper(I)-directed imine bond formation between triethylene glycol functionalized 1,2-phenylenediamine and 2,9-diformylphenanthroline subcomponents resulted in the formation of a chain in which two conjugated helical ligand strands wrap around a linear array of metal ions. Characterization data from a variety of analytical methods are consistent with our formulation of this material. After purification by dialysis, the polymer was shown to possess several properties of conceptual and practical interest. (1) Individual double-helical strands appear to further aggregate through entanglement of their side chains to form well-defined superstructures such as nanoscale bow ties and macrocycles, which can be imaged on a surface. (2) The material's copper(I) ions underwent reversible electrochemical oxidation in solution, whereas analogous model compounds were observed to decompose upon oxidation: the polymer's greater length appeared to stabilize oxidized states through delocalization or entrapment. (3) Photophysical measurements reveal this material to be photo- and electroluminescent. It has been successfully used for the fabrication of electroluminescent devices and shows a weak emission of white-blue light with CIE coordinates of (0.337, 0.359). This study further demonstrates the utility of the technique of subcomponent self-assembly for the straightforward generation of materials with useful properties.