A gold-nanoparticle stoppered [2]rotaxane

Curved Nanographenes as Stoppers in a [2]Rotaxane with Two-Photon Excited Emission

Heptagon-containing distorted nanographenes are used as stoppers for the capping of a [2]rotaxane through a Michael-type addition reaction to vinyl sulfone groups. These curved aromatics are bulky enough to prevent the disassembly of the rotaxane but also give emissive and nonlinear (two-photon absorption and emission) optical properties to the structure.

Rotaxane nanomachines in future molecular electronics

As the electronics industry is integrating more and more new molecules to utilize them in logic circuits and memories to achieve ultra-high efficiency and device density, many organic structures emerged as promising candidates either in conjunction with or as an alternative to conventional semiconducting materials such as but not limited to silicon. Owing to rotaxane's mechanically interlocked molecular structure consisting of a dumbbell-shaped molecule threaded through a macrocycle, they could be excellent nanomachines in molecular switches and memory applications. As a nanomachine, the macrocycle of rotaxane can move reversibly between two stations along its axis under external stimuli, resulting in two stable molecular configurations known as "ON" and "OFF" states of the controllable switch with distinct resistance. There are excellent reports on rotaxane's structure, properties, and function relationship and its application to molecular electronics (Ogino, et al., 1984; Wu, et al., 1991; Bissell, et al., 1994; Collier, et al., 1999; Pease, et al., 2001; Chen, et al., 2003; Green, et al., 2007; Jia, et al., 2016). This comprehensive review summarizes [2]rotaxane and its application to molecular electronics. This review sorts the major research work into a multi-level pyramid structure and presents the challenges of [2]rotaxane's application to molecular electronics at three levels in developing molecular circuits and systems. First, we investigate [2]rotaxane's electrical characteristics with different driving methods and discuss the design considerations and roles based on voltage-driven [2]rotaxane switches that promise the best performance and compatibility with existing solid-state circuits. Second, we examine the solutions for integrating [2]rotaxane molecules into circuits and the limitations learned from these devices keep [2]rotaxane active as a molecular switch. Finally, applying a sandwiched crossbar structure and architecture to [2]rotaxane circuits reduces the fabrication difficulty and extends the possibility of reprogrammable [2]rotaxane arrays, especially at a system level, which eventually promotes the further realization of [2]rotaxane circuits.

Investigation of the Complexation between 4-Aminoazobenzene and Cucurbit[7]uril through a Combined Spectroscopic, Nuclear Magnetic Resonance, and Molecular Simulation Studies

Cucurbiturils are well known for their ability to form supramolecular systems with ultrahigh affinities binding. Inclusion complex between 4-aminoazobenzene and cucurbit[7]uril has been investigated in aqueous solution by ultraviolet (UV)-spectroscopy, ¹H NMR, and molecular simulations. 4-aminoazobenzene shows high affinity in acidic solutions while no association was detected in neutral solutions. The thermodynamic properties of complex formation are investigated using both UV spectroscopy and nuclear magnetic resonance (NMR) measurements. Our results highlight that the high binding constant between CB7 and 4AA (log K = 4.9) is the result of a large negative change in Δ_r H° (-19 kJ/mol) and a small positive change in TΔ_r S° (9 kJ/mol). The analysis of the experimental data lead to hypothesis on the structure of the complex. We have used molecular dynamics simulation to interpret experiments. Interestingly, the cis-trans isomerization of aminoazobenzene is considered. All the results are discussed and compared with those previously obtained with other host molecules.

Constructing a library of metal and metal-oxide nanoparticle heterodimers through colloidal assembly

Nanoparticle dimers composed of different metals or metal oxides, as well as different shapes and sizes, are of wide interest for applications ranging from nanoplasmonic sensing to nanooptics to biomedical engineering. Shaped nanoparticles, like triangles and nanorods, can be particularly useful in applications due to the strong localized plasmonic hot-spot that forms at the tips or corners. By placing catalytic, but traditionally weakly- or non-plasmonic nanoparticles, such as metal oxides and metals like palladium, in these hot-spots, an enhanced function for sensing, photocatalysis or optical use is predicted. Here, we present an electrostatic colloidal assembly strategy for nanoparticles, incorporating different sizes, shapes and metal or metal oxide compositions into heterodimers with smaller gaps than are achievable using nanofabrication techniques. This versatile method is demonstrated on 14 combinations, including a variety of shaped gold nanoparticles as well as palladium, iron oxide, and titanium oxide nanoparticles. These colloidal nanoparticles are stabilized with traditional surfactants, such as citrate, CTAB, PVP and oleic acid/oleylamines, indicating the wide applicability of our approach. Heterodimers of gold and palladium are further analyzed using cathodoluminescence to demonstrate the tunability of these "plasmonic molecules". Since systematically altering the absorption and emission of the plasmonic nanoparticles dimers is crucial to extending their functionality, and small gap sizes produce the strongest hot-spots, this method indicates that the electrostatic approach to heterodimer assembly can be useful in creating new nanoparticle dimers for many applications.

Electrochemically switchable rotaxanes: recent strides in new directions

Are they still electrifying? Electrochemically switchable rotaxanes are well known for their ability to efficiently undergo changes of (co-)conformation and properties under redox-control. Thus, these mechanically interlocked assemblies represent an auspicious liaison between the fields of molecular switches and molecular electronics. Since the first reported example of a redox-switchable molecular shuttle in 1994, improved tools of organic and supramolecular synthesis have enabled sophisticated new architectures, which provide precise control over properties and function. This perspective covers recent advances in the area of electrochemically active rotaxanes including novel molecular switches and machines, metal-containing rotaxanes, non-equilibrium systems and potential applications.

Photo-responsive cyclodextrin/anthracene/Eu3+ supramolecular assembly for a tunable photochromic multicolor cell label and fluorescent ink

A photo-responsive supramolecular assembly was successfully constructed through the stoichiometric 2 : 1 non-covalent association of two 4-(anthracen-2-yl)pyridine-2,6-dicarboxylic acid (1) units in one γ-cyclodextrin (γ-CD) cavity, followed by the subsequent coordination polymerization of the γ-CD·1 2 (1 2 = two 1) inclusion complex with Eu(iii). Interestingly, owing to the photodimerization behavior of anthracene units and the excellent luminescence properties of Eu(iii), the Eu3+⊂γ-CD·1 2 system showed multicolor fluorescence emission from cyan to red by irradiation for 0-16 minutes. Moreover, white light emission with CIE coordinates (0.32 and 0.36) was achieved at 4 min. Importantly, white light-containing multicolor emission could be obtained in water, solid films and living cells. Especially, the Eu3+⊂γ-CD·1 2 system could tag living cells with marvelous white fluorescence and display no obvious cytotoxicity. Thus, this supramolecular assembly offers a new pathway in the fields of tunable photochromic fluorescent ink and cell labelling.