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

Abstract

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.

Dynamic Macromolecular Material Design—The Versatility of Cyclodextrin‐Based Host–Guest Chemistry

“…Nanotubes or nanoparticles were obtained by photoswitching the azobenzene units to change the geometry of the linker.AHBPO decorated with b-CD complexed with adamantyl-functionalized alkyl compounds was utilized by Zhou and co-workers to form nanotubes. [120] Moreover,t he addition of rhodamine B and 4-(2-hydroxyethylamino)-7-nitro-2,1,3-benzoxadiazole led to ah igh-efficiency artificial light harvesting system with effective distances of donor and acceptor molecules as aresult of the geometry and host/guest features of the nanotubes.…”

Artificial light-harvesting systems fabricated by supramolecular host–guest interactions

“…In 2016, Zhou et al reported the hierarchical self-assembly of a dandelion-like supramolecular polymer (DSP) into nanotubes for application in LHSs (Fig. 8) [45]. The DSPs possess a "sphere-starparachute" topological structure consisting of a spherical hyperbranched core and many parachute-like arms.…”

Hierarchical Assembly of Peptoid‐Based Cylindrical Micelles Exhibiting Efficient Resonance Energy Transfer in Aqueous Solution

“…[14] Thea dsorbed photon energy is eventually resonantly transferred to an active site at the center of the complex where it is converted into chemically stored energy.W hile many studies have been aimed at mimicking this natural light-harvesting process by achieving efficient and rapid energy transfer from donors to acceptors, [15] doing so in aqueous solution rather than in an organic environment has remained am ajor challenge. [16] Thea bility of Pep-cd cylindrical micelles to assemble and be stable in aqueous environments suggests they may offer ap latform from which to address this challenge due to several structural characteristics.F irst, they possess ahydrophobic core,w hich can serve as the "host" to accommodate hydrophobic "guest" molecules.T hus,hydrophobic donor molecules can be encapsulated inside the core and remain separated from one another to avoid p-p interactions.Second, the empty CD groups on the surface of Pep-cd cylindrical micelles can capture acceptors via ah ost-guest interaction. Third, the distance from the hydrophobic core to the surface CD groups is about 2.5 nm, which is well matched to the Fçrster radius for resonant energy transfer.…”

“…Hydrophobic NBD with af luorescence quantum yield f = 0.3 and Rhodamine Bw ith f = 0.9 were selected as donors and acceptors (Figure 7a). [16] RB was selected as the acceptor because its absorption band exhibits significant overlap with the fluorescence emission peak of NBD,t hus fulfilling one of the requirements for high FRET efficiency.I n addition, RB is an early ideal guest molecule for the host of b-CD. [17] To create the FRET-active micelles,w ei ncubated am ixture of NBD and Pep-cd monomers,l eading to co-assembly into cylindrical micelles with NBD encapsulate inside the hydrophobic core (Figure 7a).…”

“…About 2NBD molecules on average were estimated to load each 6.5 nm length of cylindrical micelles. [16,18] Afterwards,a na queous solution of RB was added into the aqueous suspension of NBD-cylindrical micelles.T he fluorescence emission spectra of the resulting structures in aqueous suspension were observed under af luorescent microscope using blue light (l = 450 nm) for ar ange of RB concentrations (Figure 7b). Ther esults show that upon addition of RB solution, the emission at 526 nm assigned to NBD donors gradually decreased, while the emission at 580 nm attributed to RB acceptors gradually increased.…”