Photoactive metallocyclodextrins: sophisticated supramolecular arrays for the construction of light activated miniature devices

The introduction of photoactive metal centres onto cyclodextrin receptors opens up new possibilities for the design of sensors, wires and energy conversion systems. This tutorial review focuses on strategies involving such metallocyclodextrins for the construction of supramolecular arrays with light-activated functions. The assembly procedures for building such arrays are presented, together with the features required for their functions both as sensors for ion or small molecule detection and as wires for photoinduced long-range energy or electron transport. Systems for metal ion sensing are described where the cyclodextrin plays a mediating role in influencing the luminescence properties of an organic probe, responsive to metal binding. Small molecule sensing by the cyclodextrin cavity is realised using luminescent lanthanide or transition metal functionalised cyclodextrins. The light signal of the photoactive metal is switched on or off upon binding an analyte in the cyclodextrin cavity. The metallocyclodextrin systems that function as wires are distinguished by the controlled assembly of transition metal polypyridine and metalloporphyrin units. These units have inherent photoactivity that defines the vectorial direction of energy or electron transfer processes through the wire.     

Magnetoluminescence in a Photostable,Brightly Luminescent Organic Radical in a Rigid Environment

We investigated the emission properties of a photostable luminescent organic radical, (3,5‐dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl radical (PyBTM), doped into host molecular crystals. The 0.05 wt %‐doped crystals displayed luminescence attributed to a PyBTM monomer with a room‐temperature emission quantum yield of 89 %, which is exceptionally high among organic radicals. The 10 wt %‐doped crystals exhibited both PyBTM monomer and excimer‐centered emission bands, and the intensity ratio of these two bands was modulated drastically by applying a magnetic field of up to 18 T at 4.2 K. This is the first observation of a magnetic field affecting the luminescence of organic radicals, and we also proposed a mechanism for this effect.     

Magnetoluminescence in a Photostable,Brightly Luminescent Organic Radical in a Rigid Environment

We investigated the emission properties of a photostable luminescent organic radical, (3,5‐dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl radical (PyBTM), doped into host molecular crystals. The 0.05 wt %‐doped crystals displayed luminescence attributed to a PyBTM monomer with a room‐temperature emission quantum yield of 89 %, which is exceptionally high among organic radicals. The 10 wt %‐doped crystals exhibited both PyBTM monomer and excimer‐centered emission bands, and the intensity ratio of these two bands was modulated drastically by applying a magnetic field of up to 18 T at 4.2 K. This is the first observation of a magnetic field affecting the luminescence of organic radicals, and we also proposed a mechanism for this effect.     

阳离子荧光敏感器的器件化问题研究

通过对石英玻片表面修饰, 制作了联有多氨基链萘基的超薄膜荧光敏感器件, 研究了它在镍、铜等金属离子水溶液及有机溶剂中的荧光猝灭现象. 发现其荧光光谱无论在水或其他有机溶剂中都存在着单体和激基缔合物(ex-cimer)的发射峰, 当处于镍离子水溶液中时, 其单体峰随离子浓度的增大出现了先增强后减弱的现象, 而激基缔合物的发光峰则仅略有减弱但变化不大. 在铜离子水溶液中其荧光的变化情况和镍离子有所不同, 对单体荧光只能观察到强度减弱的趋势, 而激基缔合物则变化不大. 比较了未联结的敏感器化合物分子在有机溶剂中荧光被铜离子猝灭的行为, 发现与其在器件表面时有很大的差别, 表明其分子结构和构象也有很大的不同.     

Overview of significant examples of electrochemical sensor arrays designed for detection of nitric oxide and relevant species in a biological environment

Ultramicroelectrode sensor arrays in which each electrode, or groups of electrodes, are individually addressable are of particular interest for detection of several species concomitantly, by using specific sensing chemistry for each analyte, or for mapping of one analyte to achieve spatio–temporal analysis. Microfabrication technology, for example photolitography, is usually used for fabrication of these arrays. The most widespread geometries produced by photolithography are thin-film microdisc electrode arrays with different electrode distributions (square, hexagonal, or random). In this paper we review different electrochemical sensor arrays developed to monitor, in vivo, NO levels produced by cultured cells or sliced tissues. Simultaneous detection of NO and analytes interacting with or released at the same time as NO is also discussed.     

Development and Application of Liquid Crystals as Stimuli-Responsive Sensors

This focused review presents various approaches or formats in which liquid crystals (LCs) have been used as stimuli-responsive sensors. In these sensors, the LC molecules adopt some well-defined arrangement based on the sensor composition and the chemistry of the system. The sensor usually consists of a molecule or functionality in the system that engages in some form of specific interaction with the analyte of interest. The presence of analyte brings about the specific interaction, which then triggers an orientational transition of the LC molecules, which is optically discernible via a polarized optical image that shows up as dark or bright, depending on the orientation of the LC molecules in the system (usually a homeotropic or planar arrangement). The various applications of LCs as biosensors for glucose, protein and peptide detection, biomarkers, drug molecules and metabolites are extensively reviewed. The review also presents applications of LC-based sensors in the detection of heavy metals, anionic species, gases, volatile organic compounds (VOCs), toxic substances and in pH monitoring. Additionally discussed are the various ways in which LCs have been used in the field of material science. Specific attention has been given to the sensing mechanism of each sensor and it is important to note that in all cases, LC-based sensing involves some form of orientational transition of the LC molecules in the presence of a given analyte. Finally, the review concludes by giving future perspectives on LC-based sensors.     

Luminescence behavior as a probe for phase transitions and excimer formation in liquid crystals: dodecylcyanobiphenyl

The luminescence behavior of a liquid crystal, dodecylcyanobiphenyl, as a function of temperature, is reported. The fluorescence intensity exhibits discontinuities at temperatures which correspond to the phase transitions: crystalline — smectic — isotropic. The results are interpreted in terms of singlet monomer and excimer formation.     

Immobilization of pyrene on quartz plate surface via a flexible long spacer and its sensing properties to dicarboxylic acids

It is known that polycyclic aromatic hydrocar-bons (PAHs) form excimer easily, and show both monomer and excimer emission in polar medium[1]. This character comes from their hydrophobic nature and plane structures. The ratio of the intensity of ex-cimer emission to that of monomer emission is a func-tion of distance between neighbouring PAHs in a sys-tem. It is not difficult to understand that many factors, such as the concentration of PAHs, temperature, pres-ence and concentration of othe…     

Circularly Polarized Luminescence of Chiral Pt(pppb)Cl (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene) Aggregate in the Excited State

We prepared enantiomers of chiral Pt^II complexes, Pt(pppb)Cl and Pt(pppb)CN (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene), and measured their CPL (circularly polarized luminescence) spectra for excimer and trimer emission. The contribution of the pinene moiety to CPL was considerably low for the π–π* emission of the monomer but large for MMLCT (metal‐metal‐to‐ligand charge‐transfer) of the excimer and trimer which had a helical structure induced in a face‐to‐face stacking fashion. The trimer CPL for (+)‐Pt(pppb)Cl was larger in intensity than that of excimer CPL; on the other hand, that for (+)‐Pt(pppb)CN was opposite in sign compared with that of excimer CPL. We conclude that differences in the excited‐state structure of the aggregate between Pt(pppb)Cl and Pt(pppb)CN account for the variation in the CPL spectra. By the aid of TD‐DFT calculations it was predicted that the dihedral angle θ(Cl‐Pt‐Pt‐Cl) was 50–60° or 110–140° for Pt(pppb)Cl aggregates and 160° for Pt(pppb)CN aggregates.     

Luminescent Sensing with Quantum Dots

Summary This review highlights recent advances in the use of quantum dots (QD’s) as luminescent sensors. The bulk of the study concentrates on systems that possess organic ligands bound to the surface of QD’s. These ligands vary from low molecular weight thiols to larger molecules such as maltose binding protein. All have one thing in common: when a target analyte binds to the ligand/receptor, a perturbation of the system occurs, that registers itself as a change in the luminescence intensity of the QD. Two main mechanisms are prevalent in controlling the luminescent intensity in such systems. The first is Photoinduced Electron Transfer (PET) and the second energy transfer. This review looks at current sensors that operate by using these mechanisms. Two component systems are also investigated where a quencher is first added to a solution of the QD, followed by addition of the target analyte that interacts with the quencher to influence the luminescence intensity.     

Photophysics of carbazole-containing systems. 1. Dilute solution behavior of poly(N-vinyl carbazole) and N-vinyl carbazole/methyl acrylate copolymers

Steady-state and time-resolved fluorescence techniques have been used to study the photophysical behaviors of poly(N-vinyl carbazole), PNVCz and a series of N-vinyl carbazole-methyl acrylate (NVCz-co-MA) copolymers in dilute solution as a function of both NVCz composition and temperature. A kinetic scheme, intended to describe intramolecular excimer formation across the entire NVCz composition range, is proposed. In low aromatic content copolymers, two monomer species (unquenched and quenched monomer) and two excimer species (the sandwich-like excimer and a higher energy excimer) exist. The contribution from monomer emission to the overall fluorescence decreases with increasing NVCz content through increased excimer formation: this is likely to be consequent upon (1) an increase in the number of excimer forming sites, and (2) increasing efficiency of energy transfer from the excited monomers to the excimer forming sites. In the homopolymer, PNVCz, the only emission that can be observed on a nanosecond timescale is excimeric. This fluorescence appears to originate from three excimer species (the sandwich-like excimer, and two higher energy forms). For the homopolymer, the current observations are consistent with the model proposed by Vandendriessche and De Schryver [Polym. Photochem. 7 , 153 (1986)]. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 963–978, 1997     

Excited-state energy transfers in single-walled carbon nanotubes functionalized with tethered pyrenes

Single-walled carbon nanotubes were co-functionalized with pyrenemethanol and 3,5-dihexadecanyloxybenzyl alcohol in different ratios with the purpose of altering the content of pyrene moieties tethered to the nanotube surface. The functionalized nanotube samples were characterized by using established instrumental techniques. The absorption and emission results of the samples suggest that there are significant “intramolecular” excited-state energy transfers from both pyrene monomer and excimer to the linked nanotube, though the energy transfer efficiencies may be different between the monomer and excimer. The excimer formation can be limited by reducing the pyrenemethanol fraction to simplify the excited state processes, but contributions from the luminescence of the well-functionalized carbon nanotubes in the same wavelength region becomes an additional complication. Mechanistic implications of the photophysical results are discussed.     

Materials for capacitive carbon dioxide microsensors capable of operating at ambient temperatures

The responses of alkylamine functionalized organic bridged polysilsesquioxanes on chemicapacitive sensors to carbon dioxide (CO₂) are described operating at temperatures ranging from 15 to 50°C. These hybrid organic–inorganic network materials were synthesized by the sol–gel polymerization of a mixture of a matrix monomer and functional monomer at various ratios followed by aging and ink-jet deposition of the sol on each capacitive sensor. During exposure of the sensor to known concentrations of analyte, the material’s capacitance was measured. From these changes in capacitance, detection limits ranging from 40 to 100 ppm were calculated. Furthermore, a correlation was observed with increasing length of the alkyl chain in the amine monomer correlating with an increase in CO₂ sensitivity and a decrease in water sensitivity. These materials offer a new method for CO₂ detection for building control systems or other low-power applications using low operating temperatures.     

Selective optical trapping and deposition of polymer and aromatic molecules from binary mixed solution

We have demonstrated size-selective optical trapping and deposition of polymer and aromatic molecules from binary mixed solution. As a near-infrared laser beam is tightly focused in polystyrene and perylene mixed solution and dropped on a glass substrate, a molecular assembly is deposited at the laser focus and fixed on the substrate. The fluorescence spectrum of the deposited microassembly depends on the laser power; perylene monomer fluorescence is dominant in the case of high laser power, whereas excimer emission of perylene crystal is observed in the case of low laser power. This suggests that polystyrene molecules are preferentially deposited by focusing a higher laser power so that the ratio of polystyrene and perylene in the assembly can be controlled by laser power. This mechanism can be explained in view of the molecular size selectivity in optical trapping.     

A long-lived luminescence and EPR bimodal lanthanide-based probe for free radicals

We developed a novel spin-labeled terbium complex Tb(3+)/cs124-DTPA-TEMPO (1) by covalently labeling a nitroxide radical on the terbium complex for monitoring free radicals of various areas. This lanthanide complex probe shows a high EPR signal which resulted from the nitroxide radical moiety, and is weakly luminescent which resulted from the intramolecular quenching effect of the nitroxide radical on sensitised terbium luminescence. The intensity of both the EPR and luminescence can be modulated by eliminating the paramagnetism of the nitroxide radical through recognition of a carbon-centered radical analyte and thus gives a quantification of the analyte. We have preliminarily applied this probe in the luminescent detection of model carbon-centered radicals and hydroxyl radicals (·OH). This probe is water-soluble and contains lanthanide-luminescence properties, favorable for the time-resolved luminescence technique. The investigation of the intramolecular quenching process has showed that the labeled nitroxide radical quenches multiple excited states of the terbium complex, resulting in highly efficient quenching of terbium luminescence. This probe is the first example of intramolecular modulation of lanthanide luminescence by a nitroxide radical.     

Normal and second excimers in macromolecules—I: Poly(1-methoxy-4-vinylnaphthalene) in fluid solution

The emission properties of poly(1-methoxy-4-vinylnaphthalene) (PMVN) in 2-methyltetrahydrofuran solution have been investigated over the range 77–350 K. It exhibits, in addition to the monomer fluorescence (348 and 360 nm), two structureless emissions derived from two different types of excimer, viz. the normal excimer (420 nm) and the second excimer (380 nm), the latter having a partially overlapping structure of aromatic rings. The intensity of second excimer emission of PMVN increases with decreasing temperature, while the normal excimer emission shows a maximum at 215 K. Kinetic analysis of transient decay curves for the fluorescence of PMVN gave results consistent with the previously reported kinetic scheme for the dimer model, 1,3-bis(4-methoxy-1-naphthyl)propane, showing that the second excimer is not formed from or converted to the normal excimer and that two types of excimer are formed independently from the excited monomer.     

The DNA three-way junction as a mould for tripartite chromophore assembly

The DNA three-way junction serves as a scaffold for the molecular organization of non-nucleosidic alkynylpyrene and perylenediimide chromophores located at the branch point of the structure. Depending on the composition of the tripartite assembly, the constructs possess distinct spectroscopic properties, ranging from monomer or excimer fluorescence to completely quenched tripartite aggregates.     

Pyrene-Capped CdSe@ZnS Nanoparticles as Sensitive Flexible Oxygen Sensors in Non-Aqueous Media

A flexible, highly sensitive sensor of oxygen in non-aqueous solvents is described. It consists of CdSe/ZnS nanoparticles decorated with a considerable number of pyrene units, thus making the formation of the pyrene excimer possible. The emission of the pyrene excimer and that of the nanoparticle are suitably separated from each other and also from the excitation wavelength. This sensor can be applied as a ratiometric oxygen sensor by using the linear response of the pyrene excimer lifetime combined with the linear response of the nanoparticle excited state lifetime. This nanohybrid has been assayed in seven media with different dielectric constants and viscosities over the whole oxygen concentration range. In addition, the sensor versatility provides an easy way for monitoring oxygen diffusion through systems.     

Excitation-Dependent Multicolour Luminescence of Organic Materials: Internal Mechanism and Potential Applications

Excitation-dependent emission (Ex-de) materials have been of considerable academic interest and have potential applications in real life. Such multicolour luminescence is a characteristic exception to the ubiquitously accepted Kasha's rule. This phenomenon has been increasingly presented in some studies on different luminescence systems; however, a systematic overview of the mechanisms underlying this phenomenon is currently absent. Herein, we resolve this issue by classifying multicolour luminescence from single chromophores and dual/ternary chromophores, as well as multiple emitting species. The underlying processes are described based on electronic and/or geometrical conditions under which the phenomenon occurs. Before we present it in categories, related photophysical and photochemical foundations are introduced. This systematic overview will provide a clear approach to designing multicolour luminescence materials for special applications.     

Supramolecular assembly system depended on guest species based on bis-naphthane modified β-cyclodextrin dimer

The supramolecular assembly system based on bis naphtahlene modified β-cyclodextrin dimer linked with ethylenediamine unit was studied. The synthesis of the titled compound (β-1) was succeeded in a 7% synthetic yield. It was observed that β-1 showed monomer emission, which was decreased concurrently with appearance of excimer emission in an addition of guest species such as 1-adamantanol or ursodeoxycholic acid. When γ-CyD was added to the system, two types of fluorescent spectra were obtained, which was depended on guest species. It was indicated that both of naphthalene units of β-1 were included in the γ-CyD cavity in the presence of 1-adamantanol in a fashion of 2:1 complex. On the other hand, an addition of ursodeoxycholic acid gave disappearance of the excimer emission as well as increase of monomer emission. In the system, each of the appended units was trapped by the each of two γ-CyDs, which is 2:2 complex formation.