Shuangqing Wang

A Rapid Aqueous Fluoride Ion Sensor with Dual Output Modes

The development of sensors and receptors for biologically important anions is currently of great interest because of their indispensable roles in vital (or physiological) processes. Among the anions, fluoride ions are one of the most attractive targets because of their considerable significance for health and environmental issues. As an essential element of the body, the U.S. Public Health Service affirmed the optimal level to be 1 mg of consumed fluoride per day. On the other hand, unnecessary and inappropriate fluoride ingestion can result in fluorosis, urolithiasis, or even cancer. The EPA (United States Environmental Protection Agency) gives an enforceable drinking water standard for fluoride of 4 mg L 1 to prevent osteofluorosis and a secondary fluoride standard of 2 mgL 1 to protect against dental fluorosis. Hence, the accurate determination of the levels of fluoride in drinking water is necessary. To date, the ion-selective electrode, ion chromatography, and standard Willard and Winter methods are generally used for quantitative fluoride analysis. However, all these methods involve disadvantages, such as complicated procedures, high costs, or low mobility. Therefore, it is important to develop highly selective, sensitive, convenient, and rapid fluoride detection methods. Fluorescent chemosensors with high specificity and sensitivity, ease, and safety of handling have received considerable attention, and a number of fluorescence sensors have been reported that are capable of detecting fluoride ions. The recognition proceeded mostly through hydrogen bonding or Lewis acid coordination, and the sensors could only be operated in organic solvents to detect tetrabutylammonium (TBA) fluoride rather than inorganic fluoride salts. This incompatibility with aqueous environments is one of the main drawbacks that restrict the application of these sensors. Unavoidable interference from H2PO4 , AcO , or CN ions is the other disadvantage. To improve the performance of fluoride sensors, another strategy based on the chemical affinity between fluoride and silicon was developed. tertButyldimethylsilyl (TBDMS) and tert-butyldiphenylsilyl (TBDPS) were chosen as additional substituents for the dye molecule, and rendered the dye unreactive to potentially interfering compounds and thus sensitive only to fluoride ions. This approach was pioneered by Kim and Swager, who developed a fluorescent fluoride receptor in organic solvents. Subsequently, several research groups reported different chemodosimeters that can probe NaF in mixtures of organic solvents and water or even pure water. However, several tens of minutes or even hours are needed to complete the detection process because low concentrations of these chemodosimeters severely reduce the reaction rate between the fluoride ions and the silyl moieties. However, the low concentration is necessary for general organic dyes to avoid fluorescence quenching induced by concentration effects, such as self-absorption and self-quenching. To date, most fluorescent sensors were based on the specific fluoride ion dependence of the emission intensity and could be significantly influenced by the excitation power and the detector sensitivity. More importantly, fluorescence intensity changes are not suitable for direct observation with the naked eye. To develop a more convenient fluorescence sensor, it is essential to make use of other fluoridedependent measurable signals other than intensity. The fluorescence color change, which can be measured directly with a colorimeter or even distinguished easily by eye, is thus a good choice. Herein we describe a rapid and portable sensor for fluoride ions in aqueous solution. The sensor, which has a high sensitivity, operates through the special affinity between fluoride ions and silicon, and provides two independent modes of signal transduction based on fluoride-dependent changes of fluorescence color (color metric mode) or intensity (power metric mode), respectively. For the design of the sensor, we chose N-(3-(benzo[d]thiazol-2-yl)-4-(hydroxyphenyl) benzamide (3-BTHPB) as an excited-state intramolecular proton transfer (ESIPT) compound. Just like other ESIPT compounds, 3-BTHPB shows two emission bands, which originate from the enol and keto forms at 418 and 560 nm, respectively. The ratio of the two bands is determined by the number of molecules that could undergo ESIPT reactions. We coupled the tert-butyldiphenylchlorosilane with the sodium salt of 3-BTHPB to afford a derivative N-(3(benzo[d]thiazol-2-yl)-4-(tert-butyldiphenyl silyloxy)phenyl)benzamide (BTTPB). As expected, BTTPB shows only blueviolet fluorescence, which was almost identical to the emission of the enol form of 3-BTHPB (see the Supporting [*] R. Hu, J. Feng, D. H. Hu, Dr. S. Q. Wang, Dr. S. Y. Li, Prof. Dr. G. Q. Yang Beijing National Laboratory for Molecular Sciences Key Laboratory of Photochemistry, Institute of Chemistry Chinese Academy of Sciences Beijing 100190 (China) Fax: (+ 86)10-8261-7315 E-mail: shayuli@iccas.ac.cn gqyang@iccas.ac.cn

A Triarylboron‐Based Fluorescent Thermometer: Sensitive Over a Wide Temperature Range

Feeling blue: the luminescence of a triarylboron compound has a high quantum yield (at least 0.64) over a wide temperature range (-50 to +100 °C) and changes from green to blue as the temperature is increased. The luminescence color was determined by the population of the two distinct excited-state conformations-a local excited state (high temperature) and a twisted intramolecular charge-transfer state (low temperature).

Understanding Solvent Effects on Luminescent Properties of a Triple Fluorescent ESIPT Compound and Application for White Light Emission

A triple fluorescent compound, N-salicylidene-3-hydroxy-4-(benzo[d]thiazol-2-yl)phenylamine (SalHBP), was dispersed in solid polymers and was developed as a white-light-emitting source in LED by using it as the first simple single compound with different configurations. The CIE coordinates were at (0.29, 0.35), close to those of pure white light. To explore speciation mechanisms in this single compound white light, SalHBP was dissolved in protic, nonpolar, and moderate polar solvent, respectively. Upon excitation, blue, green, and yellowish green emissions were observed from the three solutions at various temperatures. The conformation of SalHBP at room temperature was described by a Car-Parrinello molecular dynamics simulation. With the aid of hybrid density functional theory at the B3LYP/TZVP and PBE0/TZVP levels, three observed emission bands of SalHBP were assigned from the five most probable excited state conformations that were derived from four ground state conformations. The effect of solvent on the emission of SalHBP was summarized as a possibility for forming intermolecular hydrogen bonds between solvent and SalHBP molecules and competition between intra- and intermolecular hydrogen bonds.

Synthesis, spectroscopic and thermal properties of a series of azo metal chelate dyes

A series of azo metal chelate dyes have been synthesized. The UV-Vis absorption spectra of the azo dye and its metal complexes were measured. The stoichiometry of the complex was determined by the spectroscopic titration method to be 1:2 (ML2), and the formation constants of the complexes were evaluated. Thermal decomposition with a sharp exothermic peak was observed by TG-DT Analysis.

Engineering and geological characteristics of granite weathering profiles in South China

Granite weathering profiles are widely distributed in South China. Their engineering and geological characteristics are major geotechnical subjects that are important in the design and construction of civil engineering projects. This paper presents a summary of the weathering characteristics and zoning of granite weathering profiles in South China and discusses their engineering and geological properties. A five-grade scheme has been adopted in the zoning of a granite weathering profile. Studies have shown that the completely weathered granites (CWG) in South China have the following characteristics: low moisture content, low to medium plasticity (W-L = 22.5-39.0%; I-p = 6.5-11.8%), medium void ratio (0.36-1.29), weak shrinkage and medium compressibility (a(1-2) = 0.24-0.8 MPa-1) and high shear strength (phi = 20-30degrees; c = 20-40 KPa). The CWGs are usually at a low or high plastic state and most of them are over-consolidated soils. A majority of the physical and mechanical properties have good statistical correlations with the degree of weathering. The data presented in the paper are important in geotechnical engineering projects such as slope stability evaluation in China

Sensing in 15 s for Aqueous Fluoride Anion by Water-Insoluble Fluorescent Probe Incorporating Hydrogel

Anion recognition and sensing via artificial receptors have attracted a great deal of attention since they play a fundamental and important role in chemical, biological, medical, and environmental processes. Fluoride, as one of the smallest anions, is of particular interest because of its role in dental care and the analysis of drinking water. Herein, we invented a new method for F(-) detection by adopting the hydrogel as the supporter of reaction between a water insoluble fluorescent probe and F(-) in the water environment. This method is highly rapid, selective, and sensitive, which can determine F(-) levels in 15 s at the drinking water standard. A novel compound N-(3-(benzo[d]thiazol-2-yl)-4-(tert-butyldiphenylsilyloxy)phenyl) acetamide (BTBPA) was synthesized as the fluorescent probe because of the significant fluorescent color change from blue to green after the reaction with F(-). This method does not require the probe substances to be water-soluble, which greatly expands the range of the specific fluorescent molecules used in ion detection. Additionally, just a few microliter samples were required in the analysis procedures with this method.

Photophysical properties and optical limiting property of a soluble chloroaluminum-phthalocyanine

A chloroaluminum-phthalocyanine (AlCl-Pc) with tetra-alpha-butoxy chains (AlCl-Pc-OC4) has been synthesized and the photophysical parameters have been determined using steady-state and time-resolved absorption as well as emission spectroscopy. A luminescence from S2 excited state with long lifetime (5.71ns) is observed. A multi level model has been proposed to explain the photophysical processes after Soret-band excitation (lambdaex=355nm). The optical limiting performance for 532nm-7ns laser pulses of AlCl-Pc-OC4 has been investigated in THF solution. The sigmaex and ratio of sigmaex/sigma0 has been calculated. The good optical limiting performance is attributed to a reverse saturable absorption mechanism. It indicates that AlCl-Pc-OC4 could be promising candidates for optical limiting material.

A nonpolymeric highly emissive ESIPT organogelator with neither dendritic structures nor long alkyl/alkoxy chains

A highly fluorescent excited state intramolecular proton transfer (ESIPT) small molecular organic gelator based on 2-(2′-hydroxy)phenylbenzoxazole, N,N′-bis(4-(benzo[d]oxazol-2-yl)-3-hydroxyphenyl)-5-tert-butylisophthalamide, is developed in the present study. The ESIPT organogelator does not have a dendritic structure or long alkyl chains, but has a specific bent molecular structure. The intermolecular H-bonding (N–H⋯OC) between the J-aggregated dimers is the main driving force in the formation of the subsequent long-range one-dimensional assemblies in gel. The ESIPT gelator shows characteristics of aggregation-induced enhanced emission (AIEE). With its AIEE characteristics, ESIPT properties, simple and scalable fabrication of elongated nanobelts, as well as easy synthetic procedures, the versatile multifunctional fluorescent gelator has good prospects for future application in photoelectrical nanodevices.

Investigation of third-order nonlinearity of an azo dye and its metal-substituted compounds

Abstract The real part of third-order optical nonlinearity of an azo dye (2-(2-thiazolylazo)-5-diethylaminophenol, TAEP) and those of its copper- and cobalt-substituted compounds are measured by using femtosecond optical heterodyne optical Kerr gate technique at the wavelength of 647 nm. All the values are found to be negative. Those of Cu- and Co-substituted compounds are found to be larger than that of the metal-free dye by two and three orders of magnitude, respectively. A negative γ eff as large as 10 −29 esu is found in Co complex. We use a three-level model to characterize the nonlinear process, and suggest that π-electron delocalization in metal complex leads to an enhancement.

Intracellular Fluorescent Temperature Probe Based on Triarylboron Substituted Poly N-Isopropylacrylamide and Energy Transfer

A novel hydrophilic fluorescence temperature probe (PNDP) based on polarity-sensitive triarylboron compound (DPTB) and PNIPAM is designed and synthesized. In order to overcome the shortcomings of the single-intensity-based sensing mechanism and obtain more robust signals, ratiometric readout is achieved by designing an efficient FRET system (PNDP-NR) between DPTB and Nile Red (NR). PNDP-NR possesses some excellent features, including wide temperature range, good linear relationship, high temperature resolution, excellent reversibility, and stability. Within a sensing temperature range of 30-55 °C, the fluorescence color of PNDP-NR experiences significant change from red to green-blue. PNDP-NR is also introduced into NIH/3T3 cells to sense the temperature at the single-cell level. It gave excellent photostability and low cytotoxicity in vivo.