Stimuli-Responsive Self-Sorting Hybrid Hydrogen-Bonded/Metal-Coordinated Cage

The self-assembly of a unique molecular container is reported: a hybrid hydrogen-bonded/metal-coordinated cage where both hydrogen-bonding and metal-coordination form the crucial part of the topology. The hybrid cage was prepared combining hydrogen-bonded rosette motif and palladium(II)/platinum(II) coordination to a pyridine ligand. It was also shown that the hybrid cage could be prepared by integrative self-sorting from simple components. For the first time the genuine dual character of the hybrid cage was manifested as both self-assembling parts responded selectively to different stimuli (such as phosphine and cyanurate), which resulted in the disassembly of the cage.     

Stimuli-Responsive Resorcin[4]arene Cavitands: Toward Visible-Light-Activated Molecular Grippers

Resorcin[4]arene cavitands, equipped with diverse quinone ( Q ) and [Ru(bpy)₂dppz]²⁺ (bpy=2,2′-bipyridine, dppz=dipyrido[3,2-a:2′,3′-c]phenazine) photosensitizing walls in different configurations, were synthesized. Upon visible-light irradiation at 420 nm, electron transfer from the [Ru(bpy)₂dppz]²⁺ to the Q generates the semiquinone ( SQ ) radical anion, triggering a large conformational switching from a flat kite to a vase with a cavity for the encapsulation of small guests, such as cyclohexane and heteroalicyclic derivatives, in CD₃CN. Depending on the molecular design, the SQ radical anion can live for several minutes (≈10 min) and the vase can be generated in a secondary process without need for addition of a sacrificial electron donor to accumulate the SQ state. Switching can also be triggered by other stimuli, such as changes in solvent, host–guest complexation, and chemical and electrochemical processes. This comprehensive investigation benefits the development of stimuli-responsive nanodevices, such as light-activated molecular grippers.     

Light on the Structural Evolution of Photoresponsive Molecular Switches in Electronically Excited States

Stimuli-responsive materials are attracting extensive interest as they offer the opportunity to transform external inputs such as light into a functionality by control at the molecular level. As a result, a large number of molecular building units have been developed that enable switching between two or more states. Since the trajectory describing the transition between the various states defines the efficiency of the usually immobilized unit and the resulting functionality, it does not suffice to merely consider the initial and final states of the switching process. A key challenge is in fact to decipher at the atomic scale the actual motion that takes place after photoexcitation. Understanding and being able to manipulate this trajectory is crucial for an efficient implementation of photoactive molecular switches into functional materials, as well as to rationally develop novel tailor-made materials. In this Concept article, we highlight the potential to characterize in detail photoinitiated switching mechanisms by combining quantum chemical calculations with advanced laser spectroscopic techniques that probe the vibrational manifold of electronically excited states and its evolution.     

Remote control grubbs catalysts that modulate ring-opening metathesis polymerizations

A broad range of stimuli, including light, heat, mechanical force, or changes in chemical potential, may be used to toggle Ru-based catalysts between multiple distinct states of activity. Catalysts with such features offer a means to temporally- and, in some cases, spatially-control a variety of polymerizations, and thus should facilitate access to synthetic macromolecular materials with tunable structures and properties. Due to the intrinsic versatility and robustness of the Grubbs-type catalyst platforms, numerous remotely controlled ring-opening metathesis polymerizations have been introduced. Herein, selected examples of stimuli-responsive catalysts that have been recently used for such purposes are surveyed and discussed. Perspectives on potential opportunities for development and growth as well as an outlook for the field are also provided. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2949–2960     

刺激响应降解型聚合物水凝胶

作为一类重要的高分子材料,聚合物水凝胶由于其优良的理化性能和生物学特性而被广泛应用于生物医药领域,降解特性是其作为生物医用材料的重要性能指标。刺激响应降解型水凝胶是指在环境因素刺激下凝胶网络发生响应性断裂,进而产生凝胶-溶胶或溶胀-降解转变的一类智能高分子材料。这一响应降解特性可通过将环境敏感性断裂基团引入到聚合物凝胶网络中来实现。与水凝胶常规的水解、酶解相比,刺激响应降解因具有空间或时间上的可控特性而引起人们的广泛关注。本文重点介绍了pH响应、光响应以及氧化还原响应降解型聚合物水凝胶的设计方法、降解机理及其最新研究进展,并对刺激响应降解型水凝胶未来的研究方向进行了展望。     

界面超分子化学与响应性功能表面

超分子化学和界面的结合有效地促进了超分子化学和胶体与界面科学的发展。刺激响应性超分子界面,因在外界刺激作用下能够引起界面物理化学性质的改变并带来新的界面功能,而受到广泛的关注。近年来,溶液中基于偶氮苯 环糊精主客体相互作用的超分子组装体已经得到了广泛的研究。我们将溶液中基于偶氮苯环糊精主客体作用的可控可逆超分子组装体转移到界面上,构筑了具有刺激响应性的功能化超分子界面,并实现了表面浸润性的可逆调控、生物大分子的可控吸附与脱附、光可控的生物电化学催化等功能。我们期待类似的概念可以拓展到其他超分子体系,构筑具有特定结构的功能界面。     

Rational Construction of a Responsive Azo-Functionalized Porous Organic Framework for CO2 Sorption

An azo-functionalized porous organic framework (denoted as JJU-1) was synthesized via FeCl₃-promoted oxidative coupling polymerization. By virtue of a porous skeleton and a light/heat responsive azo functional group, this task-specific JJU-1 displays a reversible stimuli-responsive adsorption property triggered by UV irradiation and heat treatment. The initial Brunauer–Emmet–Teller (BET) surface area of this porous material is 467 m² g^–1. The CO₂ sorption isotherms exhibit a slight decrease after UV irradiation because of the trans to cis conversion of the azo functional skeleton. It is worth mentioning that the responsive CO₂ adsorption performance can be recycled for three cycles via alternating external stimuli, confirming the excellently reversible switchability of trans-to-cis isomerization and controllable CO₂ adsorption.     

Aggregation‐Induced Emission‐Active 1,4‐Dihydropyridine‐Based Dual‐Phase Fluorescent Sensor with Multiple Functions

A N‐2‐phenylethyl‐substituted 1,4‐dihydropyridine derivative (NDHP) containing 5,5‐dimethylcyclohexane‐1,3‐dione and naphthylethylene was designed and synthesized. NDHP acts as a multifunctional fluorescent sensor in dual phases. The crystal structure analysis confirms that the NDHP molecules have highly twisted conformations. The twisted conformation results in aggregation‐induced emission properties and solid‐state emission, by restricting the intramolecular free rotation in the aggregated or solid state. In the solid state, NDHP exhibits reversible mechanochromic properties as a result of the transition between the amorphous and crystalline states. NDHP also exhibits a rare phenomenon of acid‐fumed solid‐state emission enhancement owing to the change in packing mode from a zigzag arrangement to J‐aggregation. The solid‐state stimuli‐responsive fluorescence switching is applied to realize a rewritable optical recording media and a multiple output combinational logic system. In solution, NDHP shows a selective fluorescence response for environmentally harmful Hg²⁺, with a limit of detection of 2.7 nm . This results from the “turn‐on” responsive behavior owing to the Hg²⁺‐triggered aggregation of the NDHP molecules. NDHP is also used in the imaging of intracellular Hg²⁺ in HeLa cells. These findings provide a feasible and attractive route for developing multifunctional fluorescent sensors for use in dual phases.     

Construction of a Luminogen Exhibiting High Contrast and Multicolored Emission Switching through Combination of a Bulky Conjugation Core and Tolyl Groups

Stimuli‐responsive luminogens may find application in highly sensitive sensors, memories and security inks. However, few examples exhibiting both high contrast and multi‐colored emission switching have been reported due to the absence of a molecular design strategy. Through combination of large conjugation core and peripheral phenyl rings, we obtained ditolyldibenzofulvene ( 1 ). Luminogen 1 is AIE active and exhibits tetracolored emission depending on its morphology. Its three single crystals emit blue, yellow and dark orange light upon excitation, exhibiting a maximal emission of 461 nm, 545 nm and 586 nm, respectively, and its amorphous solid emits at 557 nm. All the four aggregates exhibit enhanced emission intensity at lower temperature, but only the orange‐emissive crystals exhibit blue‐shifted emission. The emission of 1 can be switched reversibly between any two of the four states through morphology tuning. Finally, the potential application of 1 in optical data storage was also investigated.