Enhanced Squaraine Rotaxane Endoperoxide Chemiluminescence in Acidic Alcohols

Squaraine rotaxane endoperoxides (SREPs) are storable chemiluminescent compounds that undergo a clean cycloreversion reaction that releases singlet oxygen and emits near-infrared light when warmed to body temperature. This study examined the effect of solvent on SREP chemiluminescence intensity and found that acidic alcohols, such as 2,2,2-trifluoroethanol, α-(trifluoromethyl)benzyl alcohol, and 1,1,1,3,3,3-hexafluoroisopropanol, greatly increased chemiluminescence. In contrast, aprotic solvents, such as trifluoroethylmethyl ether, had no effect. The interlocked rotaxane structure was necessary as no chemiluminescence was observed when the experiments were conducted with samples containing a mixture of the two non-interlocked components (squaraine thread and macrocycle endoperoxide). Spectroscopic analyses of the enhanced SREP chemiluminescent reactions showed a mixture of products. In addition to the expected squaraine rotaxane product caused by cycloreversion of the endoperoxide, a diol derivative was isolated. The results are consistent with an endoperoxide O–O bond cleavage process that is promoted by the hydrogen bonding solvent and produces light emission from a squaraine excited state.

Magnetic field-induced self-assembly of iron oxide nanocubes

Self-assembly of inorganic nanoparticles has been studied extensively for particles having different sizes and compositions. However, relatively little attention has been devoted to how the shape and surface chemistry of magnetic nanoparticles affects their self-assembly properties. Here, we undertook a combined experiment–theory study aimed at better understanding of the self-assembly of cubic magnetite (Fe₃O₄) particles. We demonstrated that, depending on the experimental parameters, such as the direction of the magnetic field and nanoparticle density, a variety of superstructures can be obtained, including one-dimensional filaments and helices, as well as C-shaped assemblies described here for the first time. Furthermore, we functionalized the surfaces of the magnetic nanocubes with light-sensitive ligands. Using these modified nanoparticles, we were able to achieve orthogonal control of self-assembly using a magnetic field and light.

A fluorescent bistable [2]rotaxane molecular switch on SiO2 nanoparticles

A fluorescent bistable [2]rotaxane was immobilized onto the surface of SiO₂ nanoparticles through click reaction. The shuttling motion of the macrocycle component was driven by external acid–base stimuli both in solution and on SiO₂ nanoparticles, accompanied by visual fluorescence changes.

Molecular and supramolecular switches on mesoporous silica nanoparticles

This review summarizes the recent advances of molecular and supramolecular switches installed on mesoporous silica nanoparticles.

Mechanistic insight into the Z–E isomerization catalysis of azobenzenes mediated by bare and core–shell gold nanoparticles

We explored the catalytic effect of 15 nm diameter gold nanoparticles (AuNPs) upon the thermal Z–E isomerization reaction of azobenzene and nine 4 and 4-4′ substituted azobenzenes (ABs).

Nanoparticle characterization based on STM and STS

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can characterize intriguing nanoparticle properties towards solid-state nanodevices.

Synthesis of a double-stranded spiroborate helicate bearing stilbene units and its photoresponsive behaviour

The sodium ion-triggered extension and contraction motions along with photo-induced cis–trans isomerisation of a photoresponsive spiroborate-based double-stranded helicate were investigated.

Dual-responsive nanoparticles that aggregate under the simultaneous action of light and CO2

Metallic nanoparticles co-functionalised with monolayers of UV- and CO₂-sensitive ligands were prepared and shown to respond to these two types of stimuli reversibly and in an orthogonal fashion.

Multiphotochromic molecular systems

We review molecular compounds encompassing several photochromic units with a focus on their functionalities.

Probing a hidden world of molecular self-assembly: concentration-dependent, three-dimensional supramolecular interconversions

A terpyridine-based, concentration-dependent, facile self-assembly process is reported, resulting in two three-dimensional metallosupramolecular architectures, a bis-rhombus and a tetrahedron, which are formed using a two-dimensional, planar, tris-terpyridine ligand. The interconversion between these two structures is concentration-dependent: at a concentration higher than 12 mg mL(-1), only a bis-rhombus, composed of eight ligands and 12 Cd(2+) ions, is formed; whereas a self-assembled tetrahedron, composed of four ligands and six Cd(2+) ions, appears upon sufficient dilution of the tris-terpyridine-metal solution. At concentrations less than 0.5 mg mL(-1), only the tetrahedron possessing an S4 symmetry axis is detected; upon attempted isolation, it quantitatively reverts to the bis-rhombus. This observation opens an unexpected door to unusual chemical pathways under high dilution conditions.

Light-responsive polymer surfaces via postpolymerization modification of grafted polymer-brush structures

Light-induced, spatially well-defined, reversible switching of surface properties enables the creation of remote-controlled smart surfaces. We have taken advantage of the unique high-resolution structuring capabilities of extreme ultraviolet (EUV) interference lithography to produce nanostructured photoresponsive polymer brushes. Patterns of poly(glycidyl methacrylate) (PGMA) and poly(methacrylic acid) (PMAA) were grafted from two different 100 μm thick fluoropolymer substrates by means of a radiation-initiated, grafting-from approach based on free-radical polymerization (FRP). Photochromic properties were introduced via novel one- or two-step postpolymerization modifications with spiropyran (SP) derivatives, which allowed us to control the number of photochromic groups on the polymer brushes. Depending on the degree of functionalization and the local chemical environment, the SP moieties can open upon UV-light exposure to form zwitterionic, deeply colored, and fluorescent merocyanines (MCs) and reclose to the colorless SP configuration via thermal or visible light-induced relaxation. Switching kinetics were studied by means of time-resolved fluorescence microscopy and compared with kinetic measurements of the SP moiety in solution. The results indicated the importance, for the intensity of the switching, of the local chemical environment provided by both the polymer brush and added solvents, and showed the predominant influence on the ring-closing kinetics of polar solvents, which stabilize the MC form. To allow further characterization of the polymer-brush arrangements on a macroscopic scale, similar, but unstructured brush systems were grafted from fluoropolymers after large-area activation using EUV radiation or argon plasma. All steps of the postpolymerization modification were characterized in detail using attenuated total reflection infrared (ATR-IR) spectroscopy. Furthermore, a light-induced reversible static-contact-angle switch with a range of up to 15° for PGMA-SP brushes and up to 30° for PMA-SP brushes was demonstrated upon alternating UV- and visible-light irradiation.

Fluorescent, MRI, and colorimetric chemical sensors for the first-row d-block metal ions

Transition metals (d-blocks) are recognized as playing critical roles in biology, and they most often act as cofactors in diverse enzymes; however, improper regulation of transition metal stores is also connected to serious disorders. Therefore, the monitoring and imaging of transition metals are significant for biological research as well as clinical diagnosis. In this article, efforts have been made to review the chemical sensors that have been developed for the detection of the first-row d-block metals (except Cu and Zn): Cr, Mn, Fe, Co, and Ni. We focus on the development of fluorescent sensors (fall into three classes: "turn-off", "turn-on", and ratiometric), colorimetric sensors, and responsive MRI contrast agents for these transition metals (242 references). Future work will be likely to fill in the blanks: (1) sensors for Sc, Ti, and V; (2) MRI sensors for Cr, Mn, Co, Ni; (3) ratiometric fluorescent sensors for Cr(6+), Mn(2+), and Ni(2+), explore new ways of sensing Fe(3+) or Cr(3+) without the proton interference, as well as extend applications of MRI sensors to living systems.

Spontaneous organization of inorganic nanoparticles into nanovesicles triggered by UV light

A novel versatile light-triggered strategy is developed to organize inorganic nanoparticles (NPs) into nanovesicles with single or multiple layers in mixed solvents. This strategy constitutes a new assembly mechanism based on the photo-oxidation of thiol ligands. Compared with currently-used individual semiconductor NPs, the prepared CdSe QD vesicles exhibit an improved catalytic activity and unprecedented catalytic stability towards solar-driven hydrogen production. This light-triggered approach to functional nanoarchitectures would lead to new opportunities in various applications.

Exploiting Hydrophobic Interactions at the Nanoscale

Hydrophobic effects are ubiquitous and manifest themselves in everyday processes such as solubilizing oil, precipitating molecules, and formation of particles or foam. Although this phenomenon is often intuitively recognized, it is not straightforward to predict it and, in particular, to control it experimentally. Hydrophobic effects are however progressively gaining recognition as an important tool providing control at the nanoscale, which may ultimately lead to the design of responsive metamaterials with unprecedented functionalities under nonequilibrium conditions.

Switchable host-guest systems on surfaces

CONSPECTUS: For device miniaturization, nanotechnology follows either the "top-down" approach scaling down existing larger-scale devices or the "bottom-up' approach assembling the smallest possible building blocks to functional nanoscale entities. For synthetic nanodevices, self-assembly on surfaces is a superb method to achieve useful functions and enable their interactions with the surrounding world. Consequently, adaptability and responsiveness to external stimuli are other prerequisites for their successful operation. Mechanically interlocked molecules such as rotaxanes and catenanes, and their precursors, that is, molecular switches and supramolecular switches including pseudorotaxanes, are molecular machines or prototypes of machines capable of mechanical motion induced by chemical signals, biological inputs, light or redox processes as the external stimuli. Switching of these functional host-guest systems on surfaces becomes a fundamental requirement for artificial molecular machines to work, mimicking the molecular machines in nature, such as proteins and their assemblies operating at dynamic interfaces such as the surfaces of cell membranes. Current research endeavors in material science and technology are focused on developing either a new class of materials or materials with novel/multiple functionalities by shifting host-guest chemistry from solution phase to surfaces. In this Account, we present our most recent attempts of building monolayers of rotaxanes/pseudorotaxanes on surfaces, providing stimuli-induced macroscopic effects and further understanding on the switchable host-guest systems at interfaces. Biocompatible versions of molecular machines based on synthetic macrocycles, such as cucurbiturils, pillararenes, calixarenes, and cyclodextrins, have been employed to form self-assembled monolayers of gates on the surfaces of mesoporous silica nanoparticles to regulate the controlled release of cargo/drug molecules under a range of external stimuli, such as light, pH variations, competitive binding, and enzyme. Rotaxanes have also been assembled onto the surfaces of gold nanodisks and microcantilevers to realize active molecular plasmonics and synthetic molecular actuators for device fabrication and function. Pillararenes have been successfully used to control and aid the synthesis of gold nanoparticles, semiconducting quantum dots, and magnetic nanoparticles. The resulting organic-inorganic hydrid nanomaterials have been successfully used for controlled self-assembly, herbicide sensing and detection, pesticide removal, and so forth, taking advantage of the selective binding of pillarenes toward target molecules. Cyclodextrins have also been successfully functionalized onto the surface of gold nanoparticles to serve as recycling extractors for C60. Many interesting prototypes of nanodevices based on synthetic macrocycles and their host-guest chemistry have been constructed and served for different potential applications. This Account will be a summary of the efforts made mainly by us, and others, on the host-guest chemistry of synthetic macrocyclic compounds on the surfaces of different solid supports.

Supramolecular chemistry at interfaces: host-guest interactions for fabricating multifunctional biointerfaces

CONSPECTUS: Host-guest chemistry can greatly improve the selectivity of biomolecule-ligand binding on account of recognition-directed interactions. In addition, functional structures and the actuation of supramolecular assemblies in molecular systems can be controlled efficiently through various host-guest chemistry. Together, these highly selective, strong yet dynamic interactions can be exploited as an alternative methodology for applications in the field of programmable and controllable engineering of supramolecular soft materials through the reversible binding between complementary components. Many processes in living systems such as biotransformation, transportation of matter, and energy transduction begin with interfacial molecular recognition, which is greatly influenced by various external stimuli at biointerfaces. Detailed investigations about the molecular recognition at interfaces can result in a better understanding of life science, and further guide us in developing new biomaterials and medicines. In order to mimic complicated molecular-recognition systems observed in nature that adapt to changes in their environment, combining host-guest chemistry and surface science is critical for fabricating the next generation of multifunctional biointerfaces with efficient stimuli-responsiveness and good biocompatibility. In this Account, we will summarize some recent progress on multifunctional stimuli-responsive biointerfaces and biosurfaces fabricated by cyclodextrin- or cucurbituril-based host-guest chemistry and highlight their potential applications including drug delivery, bioelectrocatalysis, and reversible adsorption and resistance of peptides, proteins, and cells. In addition, these biointerfaces and biosurfaces demonstrate efficient response toward various external stimuli, such as UV light, pH, redox chemistry, and competitive guests. All of these external stimuli can aid in mimicking the biological stimuli evident in complex biological environments. We begin by reviewing the current state of stimuli-responsive supramolecular assemblies formed by host-guest interactions, discussing how to transfer host-guest chemistry from solution onto surfaces required for fabricating multifunctional biosurfaces and biointerfaces. Then, we present different stimuli-responsive biosurfaces and biointerfaces, which have been prepared through a combination of cyclodextrin- or cucurbituril-based host-guest chemistry and various surface technologies such as self-assembled monolayers or layer-by-layer assembly. Moreover, we discuss the applications of these biointerfaces and biosurfaces in the fields of drug release, reversible adsorption and release of some organic molecules, peptides, proteins, and cells, and photoswitchable bioelectrocatalysis. In addition, we summarize the merits and current limitations of these methods for fabricating multifunctional stimuli-responsive biointerfaces in a dynamic noncovalent manner. Finally, we present possible strategies for future designs of stimuli-responsive multifunctional biointerfaces and biosurfaces by combining host-guest chemistry with surface science, which will lead to further critical development of supramolecular chemistry at interfaces.

The role of size and coating in Au nanoparticles incorporated into bi-component polymeric thin-film transistors

We describe the effect of blending poly(3-hexylthiophene) (P3HT) with Au nanoparticles (AuNPs) on the performance of organic thin-film transistors. To this end we have used AuNPs of two different sizes coated with chemisorbed SAMs of oligophenyl-thiols possessing increasing lengths. The electrical characteristics of the hybrid materials revealed changes in the field-effect mobility depending primarily on the AuNP size, as a result of the variable energy level of the coated metallic nanocluster and by the degree of modification of the P3HT crystalline structure.

Azobenzene-derived surfactants as phototriggered recyclable templates for the synthesis of ordered mesoporous silica nanospheres

An azobenzene-derived surfactant behaves as a "smart" molecule. Not only is it used as the structure-directing agent to synthesize unique mesoporous silica nanospheres, but it can also be quickly released from the silica framework with UV light and subsequently recycled.

TiO2-assisted photoisomerization of azo dyes using self-assembled monolayers: case study on para-methyl red towards solar-cell applications

The optical and electronic properties of a TiO2 nanoparticle-assisted photo-isomerizable surface, prepared by an azo dye/TiO2 nanocomposite film, are examined experimentally and computationally. The azo dye, para-methyl red, undergoes photoisomerization at room temperature, catalyzed by the TiO2 nanoparticle supports, while it exhibits negligible photoisomerization in solvents under otherwise identical conditions. Density functional theory and time-dependent density functional theory are employed to explain the origin of this photoisomerization in these dye···TiO2 nanoparticle self-assembled monolayers (SAMs). The device performance of these SAMs when embedded into dye-sensitized solar cells is used to further elucidate the nature of this azo dye photoisomerization and relate it to the ensuing optoelectronic properties.

Gold nanoparticles bifunctionalized by chemiluminescence reagent and catalyst metal complexes: synthesis and unique chemiluminescence property

Despite much progress in functionalized gold nanomaterial (GNMs), chemiluminescent (CL) functionalized GNMs with high CL efficiency are far from fully developed. In this work, we report a general strategy for the synthesis of gold nanoparticles (GNPs) bifunctionalized by CL reagent and catalyst metal complexes (BF-GNPs) by taking N-(aminobutyl)-N-(ethylisoluminol) (ABEI) as a model of CL reagents. The complexes of 2-[bis[2-[carboxymethyl-[2-oxo-2-(2-sulfanylethylamino)ethyl]amino]ethyl]amino]acetic acid (DTDTPA) with various metal ions, including Co(2+), Cu(2+), Pb(2+), Ni(2+), Hg(2+), Cr(3+), Eu(3+), La(3+), Gd(3+), Sm(3+), Er(3+), Dy(3+), Ce(4+), and Ce(3+), were grafted on the surface of ABEI functionalized GNPs (ABEI-GNPs) to form a series of BF-GNPs. These BF-GNPs exhibited excellent CL activity. In particular, the CL intensity of DTDTPA/Co(2+)-ABEI-GNPs was over 3 orders of magnitude higher than ABEI-GNPs. This work demonstrates for the first time that metal complexes grafted on the surface of GNPs have unique catalytic activity on the CL reaction, superior to that in the liquid phase. Such BF-GNPs may find future applications in bioassays, microchips, and molecular/cellular imaging.

Ultrasensitive photoreversible molecular sensors of azobenzene-functionalized plasmonic nanoantennas

This Letter describes an unprecedentedly large and photoreversible localized surface plasmon resonance (LSPR) wavelength shift caused by photoisomerization of azobenzenes attached to gold nanoprisms that act as nanoantennas. The blue light-induced cis to trans azobenzene conformational change occurs in the solid state and controls the optical properties of the nanoprisms shifting their LSPR peak up to 21 nm toward longer wavelengths. This shift is consistent with the increase in thickness of the local dielectric environment (0.6 nm) surrounding the nanoprism and perhaps a contribution from plasmonic energy transfer between the nanoprism and azobenzenes. The effects of the azobenzene conformational change and its photoreversibility were also probed through surface-enhanced Raman spectroscopy (SERS) showing that the electronic interaction between the nanoprisms and bound azobenzenes in their cis conformation significantly enhances the intensity of the Raman bands of the azobenzenes. The SERS data suggests that the isomerization is controlled by first-order kinetics with a rate constant of 1.0 × 10(-4) s(-1). Our demonstration of light-induced photoreversibility of this type of molecular machine is the first-step toward removing present limitations on detection of molecular motion in solid-state devices using LSPR spectroscopy with nanoprisms. Modulating the LSPR peak position and controlling energy transfer across the nanostructure-organic molecule interface are very important for the fabrication of plasmonic-based nanoscale devices.

Guest dependent dielectric properties of nickel(ii)-based supramolecular networks

Nickel-based supramolecular compounds exhibit interesting guest dependent dielectric behaviour and high thermal stability. This study serves as a motivation to expand our research to create both high and low-κmaterials with a judicious selection of guest molecules.

SCO@SiO2@Au core–shell nanomaterials: enhanced photo-thermal plasmonic effect and spin-crossover properties

[Fe(Htrz)₂(trz)](BF₄)@SiO₂@Au core–shell spin-crossover nanocomposites have been successfully synthesized, and Au nanoparticles caused an efficient photo-thermal heating in the nanocomposites and influenced the spin-transition behaviors.

Ultra-small gold nanoparticles synthesized in aqueous solution and their application in fluorometric collagen estimation using bi-ligand functionalization

Ultra-small hydrosol LBH-AuNPs were synthesized, and their application in the FRET based estimation of collagen investigated using bi-ligand functionalised LBH-AuNPs.

Chemical consequences of mechanical bonding in catenanes and rotaxanes: isomerism, modification, catalysis and molecular machines for synthesis

We highlight some of the less discussed consequences of mechanical bonding for the chemical behaviour of catenanes and rotaxanes, including striking recent examples where molecular motion controls chemical reactions.

Photocontrol of luminescent inorganic nanocrystals via an organic molecular switch

The photoluminescence of ZnO nanocrystals is reversibly modulated via a diarylethene photoswitch, and the photophysics mechanism was unraveled.

Photochromic–fluorescent–plasmonic nanomaterials: towards integrated three-component photoactive hybrid nanosystems

Silica-coated gold nanorods functionalized with grafted fluorescent and photochromic derivatives were synthesized and cross-coupled interactions between plasmonic, photochromic, and fluorescence properties have been demonstrated.

Cytochrome C capped mesoporous silica nanocarriers for pH-sensitive and sustained drug release

Drug nanocarriers with pH-sensitive and sustained drug release properties were constructed by using cytochrome C as a pore blocker to achieve high therapeutic efficacy for cancer.