Consecutive complex aggregation pathway in covalent helical polymer-metal complexes: nanospheres with controlled P/M macroscopic chirality

Abstract

Kinetically trapped and thermodynamic nanospheres with opposite macroscopic P/M chirality and opposite circularly polarized luminescence (CPL) can be obtained from a single helical polymer-metal complex under the same environmental conditions. To prepare these nanospheres, a chiral poly(diphenylacetylene) (PDPA) [poly-(L)-1] with a large energy barrier between the P and M helical senses is chosen as source of chirality, while Ba2+ metal ions are selected as crosslinking agents. As a result, the poly-(L)-1/Ba2+ complex can generate both kinetically trapped (Agg1, M nanospheres) and thermodynamic (Agg2, P nanospheres) aggregates, which can be dispersed in the same solvent. Due to the high energy barrier of the helix inversion process for poly-(L)-1, the complete evolution from the kinetically trapped aggregate (Agg1, M nanospheres) to the thermodynamic one (Agg2, P nanospheres) takes more than 75 days at room temperature, which can be accelerated at higher temperatures. These nanospheres are stable and remain dispersed in solution for up to 8 months without further aggregation.