Precision Chemistry of Metallofullerenes and Graphene: Recent Advances.

Precision chemistry of synthetic carbon allotropes including fullerene and graphene, characterized by a well-controlled and spatially resolved addends bonding, has received widespread attention owing to its capability to tailor their physicochemical properties for high-end applications. In the context of fullerene, particularly endohedral metallofullerenes (EMFs), precision chemistry emphasizes the regioselective binding of a specific number of moieties to the fullerene cage. In the case of graphene, precision chemistry focuses on achieving precise patterning and tailored modifications. Inspired by their intriguing advantages, the precision chemistry of these two members has witnessed rapid advancements. While existing reviews have outlined advancements in the precision chemistry of EMFs and graphene, this review uniquely concentrates on the most recent progress. Finally, the prospects in this field, with a special focus on the potential for creating functional materials through strategically patterned binding of fullerene and graphene networks are envisioned.

Controlled Self-Assembly of Multiple-Responsive Superamphiphilc Polymers Based on Host-Guest Inclusions of a Modified PEG with ß-Cyclodextrin.

Superamphiphilic polymers (SAPs) constructed by host-guest inclusion can self-assemble into various nanostructures in solution, which can find applications in many fields such as nanodevices, drug delivery, and template synthesis. Herein, we report the controlled self-assembly of multiple-responsive SAP based on a selective host-guest inclusion of ß-cyclodextrin (ß-CD) with a modified poly(ethylene glycol) (PEG) (FcC11AzoPEG) consisting of a ferrocene (Fc) end group, a C11 alkyl chain, an azobenzene (Azo) block, and a poly(ethylene glycol)methyl ether (PEG) chain. These SAPs can self-assemble into interesting nanostructures in water upon exposure to different stimuli because ß-CD can be selectively included with different guests, such as Fc, Azo, and C11 alkyl chain, under different stimuli. The inclusion complex of Fc with ß-CD (Fc@ß-CD SAP) can form nanowire micelles in aqueous solution. The nanowire micelles can be transformed into spindle micelles with the addition of oxidant because the majority of ß-CDs dissociated from the complex Fc@ß-CD SAP due to a conversion of Fc to Fc+ and will preferentially include with Azo group to form another dominant inclusion complex (Azo@ß-CD SAP). After UV irradiation, the spindle micelles can be further transformed into spherical micelles because most of ß-CDs are excluded from the complex Azo@ß-CD SAP due to a trans- to cis-Azo conversion and then form a dominant inclusion complex with C11 alkyl chains (C11@ß-CD SAP). This work not only demonstrates the selective host-guest inclusion of stimuli-responsive groups modified PEG with ß-CD but also provides a useful approach for construction of diverse morphologies.

Ferrocene-Functionalized Hydrophobically Modified Ethoxylated Urethane: Redox-Responsive Controlled Self-Assembly and Rheological Behavior in Aqueous Solution.

In this work, we present a novel redox-responsive ferrocene-functionalized hydrophobically modified ethoxylated urethane (Fc-HEUR) model polymer. The effects of a redox-induced hydrophobicity change of ferrocenyl hydrophobes on the self-assembly and rheological properties of Fc-HEUR in aqueous solution were investigated. In view of the redox-induced change in the hydrophilic-lipophilic balance of polymers, the Fc-HEUR polymer in aqueous solution can reversibly self-assemble into spherical micelles and larger micellar aggregates of different nanoscales and also disassemble by redox reactions immediately. Moreover, we have demonstrated that a rearrangement of micellar junctions takes place through a bridge-loop or loop-bridge transition in the concentrated polymer solution followed by redox reactions, which induces a great change in the rheological properties of the polymer solution: a viscoelastic liquid for the reduction state Fc-HEUR and a viscous liquid for the oxidation state Fc+-HEUR, owing to their different relaxation behaviors. Particularly, the associative structures and rheological properties of the Fc-HEUR aqueous solution can be reversibly controlled by redox reactions. This work will be useful not only for understanding of the thickening mechanism of stimuli-responsive HEURs but also for the development of reversible self-assembly and controlled rheological fluids, which may have some special application in drug delivery systems, catalyst supports, sensors, and microfluidic devices.

Spiropyran-Decorated SiO2-Pt Janus Micromotor: Preparation and Light-Induced Dynamic Self-Assembly and Disassembly.

The controlled self-assembly of self-propelled Janus micromotors may give the micromotors some potential applications in many fields. In this work, we design a kind of SiO2-Pt Janus catalytic micromotor functionalized by spiropyran (SP) moieties on the surface of the SiO2 hemisphere. The spiropyran-modified SiO2-Pt Janus micromotor exhibits autonomous self-propulsion in the presence of hydrogen peroxide fuel in N,N-dimethylformamide (DMF)/H2O (1:1 in volume) mixture. We demonstrate that the self-propelled Janus micromotors can dynamically assemble into multiple motors because of the electrostatic attractions and π-π stacking between MC molecules induced by UV light irradiation (λ = 365 nm) and also quickly disassemble into mono motors when the light is switched to green light (λ = 520 nm) for the first time. Furthermore, the assembled Janus motors can move together automatically with different motion patterns propelled by the hydrogen peroxide fuels upon UV irradiation. The work provides a new approach not only to the development of the potential application of Janus motors but also to the fundamental science of reversible self-assembly and disassembly of Janus micromotors.

Voltage-responsive reversible self-assembly and controlled drug release of ferrocene-containing polymeric superamphiphiles.

A new type of voltage-responsive comb-like superamphiphilic block polymer PEG113-b-PAA30/FTMA was prepared by the electrostatic interactions of an ionic ferrocenyl surfactant (FTMA) and an oppositely charged double-hydrophilic block polyelectrolyte poly-(ethylene glycol)-b-poly(acrylic acid) (PEG113-b-PAA30) in aqueous solution. An in situ electrochemical redox system was designed to research its electrochemical activity in aqueous solution. The polymeric superamphiphile PEG113-b-PAA30/FTMA could reversibly aggregate to form spherical micelles of 20-30 nm diameter in aqueous solution, and also disaggregate into irregular fragments by an electrochemical redox reaction when its concentration is in the range of the critical aggregation concentration (cacred) of the reduction state to its cacox of the oxidation state. Interestingly, above cacox, the superamphiphile can aggregate into spherical micelles of 20-30 nm diameter, which can be transformed into larger spherical micelles of 40-120 nm diameter after electrochemical oxidation, and reversibly recover initial sizes after electrochemical reduction. Moreover, this reversible self-assembly process can be electrochemically controlled just by changing its electrochemical redox extent without adding any other chemical reagent. Further, rhodamine 6G (R6G)-loaded polymeric superamphiphile aggregates have been successfully used for the voltage-controlled release of loaded molecules based on their voltage-responsive self-assembly, and the release rate of R6G could be mediated by changing electrochemical redox potentials and the concentrations of polymeric superamphiphiles. Our observations witness a new strategy to construct a voltage-responsive reversible self-assembly system.

Novel ferrocenyl-terminated linear-dendritic amphiphilic block copolymers: synthesis, redox-controlled reversible self-assembly, and oxidation-controlled release.

Novel linear-dendritic amphiphilic block copolymers with hydrophilic poly(ethylene glycol) (PEG) block and hydrophobic Percec-type dendrons containing ferrocenyl terminals were synthesized by the esterification reaction of poly(ethylene glycol) methyl ether with ferrocenyl-terminated alkyl-substituted benzoic acid dendrons. On the basis of the results that the critical aggregation concentration (CACox) of the oxidation state polymer is much higher than CACred of the corresponding reduction state, these polymers can reversibly self-assemble into various aggregates, such as spherical, wormlike micelles, and vesicles, and also disassemble into irregular fragments in aqueous solution by redox reaction when changing the polymer concentrations. Copolymer PEG45-b-Fc3 (3) with 3,4,5-tris(11-ferrocenylundecyloxy) benzoic acid (2) can self-assemble into nanoscale wormlike micelles when the polymer concentration in aqueous solution is above its CACox. These wormlike micelles can be transformed into nanosized vesicles by Fe2(SO4)3 and regained by vitamin C. Interestingly, copolymer PEG45-b-Fc2 (5) with 3,5-bis(11-ferrocenylundecyloxy) benzoic acid (4) can reversibly self-assemble into spherical micelles with two different sizes by redox reaction above the CACox, indicating that the terminal hydrophobic tail number of dendrons plays a key role in determining the self-assembled structures. Furthermore, rhodamine 6G (R6G)-loaded polymer aggregates have been successfully used for the oxidation-controlled release of loaded molecules, and the release rate can be mediated by the concentrations of oxidant and copolymers. The results provide an effective approach to the reversible self-assembly of linear-dendritic amphiphilic block copolymers and also promise the potential of these novel redox-responsive amphiphilic block copolymers in drug delivery systems, catalyst supports, and other research fields.