Decoupling optical properties in metallo-supramolecular poly(p-phenylene ethynylene)s

The self-assembly polymerization of ditopic macromolecules through metal-ligand binding is an attractive framework for the preparation of high-molecular-weight metallo-supramolecular polymers. This approach was utilized here for the polymerization of a conjugated macromonomer (1) that was derived by functionalizing a low-molecular-weight poly(2,5-dialkoxy-p-phenylene ethynylene) (PPE) core with 2,6-bis(1′-methylbenzimi-dazolyl)pyridine (Mebip) ligands on the two terminal positions. To minimize electronic interactions between the PPE moieties and the metal-ligand complexes, nonconjugated hexamethylene spacers were introduced between the PPE and Mebip building blocks. The supramolecular polymerization of macromonomer 1 with equimolar amounts of Zn²⁺ or Fe²⁺ resulted in polymers, which exhibit appreciable mechanical properties (loss moduli of [1·Zn(ClO₄)₂]_n and [1·Fe(ClO ₄)₂]_n at 25 °C are ca. 450 and 610 MPa, respectively), but on account of their dynamic, reversible nature offer the ease of processing of low-molecular-weight compounds. The optoelectronic properties of these metallopolymers are similar to those of the parent PPE and demonstrate that the functionalities of semiconducting building blocks and coordination chain extenders can be effectively decoupled by a short, nonconjugated spacer.