Mechanical Training Enabled Reinforcement of Polyrotaxane-Containing Hydrogel.

Many strategies have been developed for constructing anisotropic hydrogels, however, it remains a challenge to fabricate hydrogels with anisotropic nanocrystalline domains from intrinsically soft networks. Here, we report a naphthotube-based polyrotaxane-containing hydrogel that can be reinforced via mechanical training. During the training process, the hydrogel can adopt reorientation of polymer chains to form anisotropic structures driven by external uniaxial force. Due to the multiple hydrogen bonding sites and movable feature of naphthotube, the sliding of naphthotube on PEG chains simultaneously inducing the zipping of adjacent polymer chains to form densely anisotropic nanocrystalline domains through hydrogen bonded networks. Thus, the trained hydrogel exhibits an enhanced tension stress of ≈110 kPa, which realize a remarkable enhancement of ≈10 times compare to initial state. This study provides a new tactic for improving the mechanical performance of soft materials.

Non-Equilibrium Kinetic States of a [2]Rotaxane-Based Molecular Shuttle Controlled by Acid Concentrations.

A [2]rotaxane-based molecular shuttle with an acid-responsive asymmetric macrocycle on a symmetric dumbbell axle is reported. Upon adding TFA, the macrocycle, namely the amine naphthotube, is protonated and translocates from the di(quaternary ammonium) station to the triazole stations because of electrostatic repulsion and weakened binding. The shuttling kinetics are slow due to the steric hindrance caused by the ethyl group on the quaternary ammonium center and can be followed by 1 H NMR spectroscopy. Interestingly, it was found that the shuttling kinetics depends on the concentration of TFA. A kinetic intermediate was detected and can even be captured in the presence of a high concentration of TFA. Extensive control experiments revealed that the shuttling kinetics and the capture of the kinetic intermediate are related to the different protonation states of the rotaxanes.

Molecular recognition and spectral tuning of organic dyes in water by amide naphthotubes.

Molecular recognition and spectral tuning of 13 organic dyes were achieved in water by amide naphthotubes. The association affinity to a styryl derivative is up to 4.5 × 107 M-1, which is the highest among all the known hosts. In addition, great fluorescence enhancement was observed for styryl derivatives. This would lay a basis for the potential analysis application.

Visible-Light-Triggered Selective Intermolecular [2+2] Cycloaddition of Extended Enones: 2-Oxo-3-enoates and 2,4-Dien-1-ones with Olefins.

Photosensitization has recently re-emerged owing to the current interest in visible-light catalysis. One of the photoreactions investigated in this context, namely, photo[2+2]cycloaddition of olefins, is established to show high selectivity and wide generality. Here, we describe the results of our studies on selective intermolecular cycloaddition between extended enones (2,4-dien-1-ones and 2-oxo-3-enoates) and olefins under visible-light sensitization. With Ru(bpy)3Cl2 as the triplet energy sensitizer, [2+2] addition of 2,4-dien-1-ones to olefins resulted in the addition to the "ene" part of enones with high efficiency. Generality and functional group tolerance were established by examining a number of enones. 2-Oxo-3-enoates also underwent addition to olefins in the presence of Ru(phen)3(PF6)2. Both additions were more efficient in the presence of the triplet sensitizer than upon direct irradiation. No Paternò-Büchi product was detected. Density functional theory calculations revealed the origin of high selectivity in the two extended enone systems. Together with spectroscopic studies and control experiments, the cycloaddition has been demonstrated to occur from the excited triplet state of these extended enones, which were generated via the energy transfer process.

General and Efficient Intermolecular [2+2] Photodimerization of Chalcones and Cinnamic Acid Derivatives in Solution through Visible-Light Catalysis.

[2+2] Photocycloaddition, for example, the dimerization of chalcones and cinnamic acid derivatives, is a unique strategy to construct cyclobutanes, which are building blocks for a variety of biologically active molecules and natural products. However, most attempts at the above [2+2] addition have focused on solid-state, molten-state, or host-guest systems under ultraviolet-light irradiation in order to overcome the competition of facile geometric isomerization of nonrigid olefins. We report a general and simple method to realize the intermolecular [2+2] dimerization reaction of these acyclic olefins to construct cyclobutanes in a highly regio- and diastereoselective manner in solution under visible light, which provides an efficient solution to a long-standing problem.

Photocatalysis with Quantum Dots and Visible Light: Selective and Efficient Oxidation of Alcohols to Carbonyl Compounds through a Radical Relay Process in Water.

Selective oxidation of alcohols to aldehydes/ketones has been achieved with the help of 3-mercaptopropionic acid (MPA)-capped CdSe quantum dot (MPA-CdSe QD) and visible light. Visible-light-prompted electron-transfer reaction initiates the oxidation. The thiyl radical generated from the thiolate anion adsorbed on a CdSe QD plays a key role by abstracting the hydrogen atom from the C-H bond of the alcohol (R1 CH(OH)R2 ). The reaction shows high efficiency, good functional group tolerance, and high site-selectivity in polyhydroxy compounds. The generality and selectivity reported here offer a new opportunity for further applications of QDs in organic transformations.

The singlet excited state of BODIPY promoted aerobic cross-dehydrogenative-coupling reactions under visible light.

In contrast to previous studies, we disclose for the first time that the singlet excited state ((1)PS*) of BODIPY rather than the triplet excited state ((3)PS*) can drive C-H bond activation to form C-C and C-P bonds smoothly, which offers new methods to promote organic transformation under visible light irradiation.

A unique 1,2-acyl migration for the construction of quaternary carbon by visible light irradiation of platinum(II) polypyridyl complex and molecular oxygen.

A unique 1,2-acyl migration for the construction of quaternary carbon in a one-pot reaction under visible light is described. By irradiating a platinum(II) polypyridyl complex with visible light, enamine 1 is able to react with alcohol 2 to yield compound 3 featuring a quaternary carbon via 1,2-acyl migration and concurrent esterification. Studies on the mechanism reveal that the platinum(II) complex is able to generate singlet oxygen ((1)O2) that is responsible for this unprecedented intramolecular 1,2-acyl migration transformation.