Hierarchical Self-Assembly of a Dandelion-Like Supramolecular Polymer into Nanotubes for use as Highly Efficient Aqueous Light-Harvesting Systems

A dandelion-like supramolecular polymer (DSP) with a sphere-star-parachute topological structure consisting of a spherical hyperbranched core and many parachute-like arms is constructed by the non-covalent host-guest coupling between a cyclodextrin-endcapped hyperbranched multi-arm copolymer (host) and many functionalized adamantanes with each having three alkyl chain arms (guests). The obtained DSPs can further self-assemble into nanotubes in water in a hierarchical way from vesicles to nanotubes through sequential vesicle aggregation and fusion steps. The nanotubes have a bilayer structure consisting of multiple hydrophobic-hyperbranched-hydrophilic layers. Such a structure is very useful for constructing a chlorosome-like artificial aqueous light-harvesting system, as demonstrated here, via the incorporation of hydrophobic 4-(2-hydroxyethylamino)-7-nitro-2,1,3-benzoxadiazole as donors inside the hyperbranched cores of the nanotubes and the hydrophilic Rhodamine B as the acceptors immobilized on the nanotube surfaces. This as-prepared nanotube light harvesting system demonstrates unexpectedly high energy transfer efficiency (above 90%) in water. This extends supramolecular polymers with more complex topological structure, special self-assembly behavior, and new functionality.