Yuming Yang,†,§ Qiang Zhao,‡,§ Wei Feng,† and Fuyou Li*,† †Department of Chemistry and State Key Laboratory of Molecular Engineering of Polymers and Institutes of Biomedical Sciences, Fudan University, Shanghai 200433, P. R. China ‡Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, Nanjing 210046, P. R. China.

Luminescent chemodosimeters for bioimaging.

Design strategies for water-soluble small molecular chromogenic and fluorogenic probes.

This paper reviews recent studies on the semiconductor photocatalysis based on surface-modified TiO2 of which application is mainly focused on environmental remediation. TiO2 photocatalysis that is based on the photoinduced interfacial charge transfer has been extensively studied over the past four decades. A great number of modification methods of semiconductor photocatalysts have been developed and investigated to accelerate the photoconversion, to enable the absorption of visible light, or to alter the reaction mechanism to control the products and intermediates. In this regard, various modification methods of TiO2 are classified according to the kind of surface modifiers (metal-loading, impurity doping, inorganic adsorbates, polymer coating, dye-sensitization, charge transfer complexation) and their effects on photocatalytic reaction mechanism and kinetics are discussed in detail. Modifying TiO2 in various ways not only changes the mechanism and kinetics under UV irradiation but also introduces visible light activity that is absent with pure TiO2. Each modification method influences the photocatalytic activity and mechanism in a way different from others and the observed modification effects are often different depending on the test substrates and conditions even for the same modification method. Better understanding of the modification effects on TiO2 photocatalysis is necessary to obtain reliable results, to assess the photoconversion efficiency more quantitatively, and to further improve the modification methods.

Surface modification of TiO2 photocatalyst for environmental applications

Coordination chemistry plays an essential role in the design of photoluminescent probes for metal ions. Metal coordination to organic dyes induces distinct optical responses which signal the presence of metal species of interest. Luminescent lanthanide (Ln(3+)) and transition metal complexes of d(6), d(8) and d(10) configurations often exhibit unique luminescence properties different from organic dyes, such as high quantum yield, large Stokes shift, long emission wavelength and emission lifetimes, low sensitivity to microenvironments, and can be explored as lumophores to construct probes for metal ions, anions and neutral species. In this review, the design principles and coordination chemistry of metal probes based on mechanisms of PeT, PCT, ESIPT, FRET, and excimer formation will be discussed in detail. Particular attention will be given to rationales for the design of turn-on and ratiometric probes. Moreover, phosphorescent probe design based on Ln(3+) and d(6), d(8) and d(10)-metal complexes are also presented via discussing certain factors affecting the phosphorescence of these metal complexes. A survey of the latest progress in photoluminescent probes for identification of essential metal cations in the human body or toxic metal cations in the environment will be presented focusing on their design rationales and sensing behaviors. Metal complex-based photoluminescent probes for biorelated anions such as PPi, and neutral biomolecules ATP, NO, and H(2)S will be discussed also in the context of their metal coordination-related sensing behaviors and design approaches.

Metal coordination in photoluminescent sensing

Principle has it that even the most advanced super-resolution microscope would be futile in providing biological insight into subcellular matrices without well-designed fluorescent tags/probes. Developments in biology have increasingly been boosted by advances of chemistry, with one prominent example being small-molecule fluorescent probes that not only allow cellular-level imaging, but also subcellular imaging. A majority, if not all, of the chemical/biological events take place inside cellular organelles, and researchers have been shifting their attention towards these substructures with the help of fluorescence techniques. This Review summarizes the existing fluorescent probes that target chemical/biological events within a single organelle. More importantly, organelle-anchoring strategies are described and emphasized to inspire the design of new generations of fluorescent probes, before concluding with future prospects on the possible further development of chemical biology.

Discerning the Chemistry in Individual Organelles with Small-Molecule Fluorescent Probes.

Rhodamine-based fluorescent sensor for mercury in buffer solution and living cells

A bulk-embedded TiO2-based nanohybrid material with WO3 clusters as the electron storage sites was designed and prepared. Conduction band electrons generated upon excitation of TiO2 were successfully stored in this nanohybrid material in the presence of O2, and the storage of electrons in WO3 clusters was further confirmed by the electron spin resonance (ESR) measurements. It is found that the reduction of oxygen on the surface of nanohybrid particles was much slower than that on pristine TiO2. Synthesis conditions were varied to optimize the storage behaviors of hybrid materials. The structure of the nanohybrid material was investigated using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), Raman, and X-ray diffraction. Potential environmental application of this nanohybrid material for the reduction treatment of poisonous heavy metal ions without in situ light irradiation was explored.

Photoinduced Electron Storage in WO3/TiO2 Nanohybrid Material in the Presence of Oxygen and Postirradiated Reduction of Heavy Metal Ions

After several decades of development, fluorescent sensors have been recognised as indispensable and efficient molecular tools that can help monitor and visualise cations or biomolecules with high sensitivity and spatial resolution in live cells or tissues. Undoubtedly, our understanding of metal ion homeostasis in biology has significantly benefited from advancements of fluorescent sensors for metal ions. Zn has attracted significant attention because of its critical role in many biological processes. In spite of worthy attentions on cytosolic Zn , the function of Zn in subcellular compartments, such as mitochondria, endoplasmic reticulum, and Golgi, and underlying dependence between these Zn and cellular processes are still not established well. Hence, developing targetable fluorescent sensors for monitoring the zinc level in specific organelles will contribute significantly to addressing these issues. Since the fluorescent sensor TSQ was first applied to in vitro imaging of Zn , numerous Zn sensors have been archived in the past few years. However, only a few smallmolecule fluorescent or genetically encoded zinc sensors have been designed to target organelles. Moreover, most of these sensors read out the ion-binding event by emission intensity changes based on the photoinduced electron transfer (PeT) mechanism. Theoretically, this type of sensor can provide quantitative measurements of Zn , but it is infeasible to quantify Zn in live cells by these zinc fluorescent sensors because their emission intensity is significantly influenced by many other factors, such as the sample environment, sensor concentration, bleaching, and instrumental efficiency. A ratiometric sensor with self-calibration with dual emission maxima can eliminate most or all ambiguities and could be an ideal solution for quantitatively measuring intracellular ions. So far, various ratiometric Zn-selective sensors are available, but unfortunately, only several examples of ratiometric and targetable sensors have been realised. Design of targetable and ratiometric sensors for quantification of Zn in specific organelles is, therefore, important, yet remains as one of the greatest challenges. To this end, we designed a fluorescent sensor, DQZn2, for ratiometric detection of mitochondrial Zn (Scheme 1). On

A Ratiometric and Targetable Fluorescent Sensor for Quantification of Mitochondrial Zinc Ions

The hydroxylation process is the primary, and even the rate-determining step of the photocatalytic degradation of aromatic compounds. To make clear the hydroxylation pathway of aromatics, the TiO2 photocatalytic hydroxylation of several model substrates, such as benzoic acid, benzene, nitrobenzene, and benzonitrile, has been studied by an oxygen-isotope-labeling method, which can definitively assign the origin of the O atoms (from oxidant O2 or solvent H2O) in the hydroxyl groups of the hydroxylated products. It is found that the oxygen source of the hydroxylated products depends markedly on the reaction conditions. The percentage of the products with O2-derived hydroxyl O atoms increases with the irradiation time, while it decreases with the increase of substrate concentration. More intriguingly, when photogenerated valence-band holes (hvb+) are removed, nearly all the O atoms (>97 %) in the hydroxyl groups of the hydroxylated products of benzoic acid come from O2, whereas the scavenging of conduction-band electrons (ecb−) makes almost all the hydroxyl O atoms (>95 %) originate from solvent H2O. In the photocatalytic oxidation system with benzoic acid and benzene coexisting in the same dispersion, the percentage of O2-derived hydroxyl O atoms in the hydroxylated products of strongly adsorbed benzoic acid (ca. 30 %) is much less than in that of weakly adsorbed benzene (phenol) (>60 %). Such dependences provide unique clues to uncover the photocatalytic hydroxylation pathway. Our experiments show that the main O2-incorporation pathway involves the reduction of O2 by ecb− and the subsequent formation of free .OH via H2O2, which was usually overlooked in the past photocatalytic studies. Moreover, in the hydroxylation initiated by hvb+, unlike the conventional mechanism, the O atom in O2 cannot incorporate into the product through the direct coupling between molecular O2 and the substrate-based radicals.

Pathway of Oxygen Incorporation from O2 in TiO2 Photocatalytic Hydroxylation of Aromatics: Oxygen Isotope Labeling Studies

The study of the micelle-to-vesicle transition (MVT) is of great importance from both theoretical and practical points of view. Herein, we studied the effect of compressed CO 2 on the aggregation behavior of dodecyltrimethylammonium bromide (DTAB)/sodium dodecyl sulfate (SDS) mixed surfactants in aqueous solution by means of direct observation, turbidity and conductivity measurements, steady-state fluorescence, time-resolved fluorescence quenching (TRFQ), fluorescence quantum yield, and template methods. Interestingly, all these approaches showed that compressed CO 2 could induce the MVT in the surfactant system, and the vesicles returned to the micelles simply by depressurization; that is, CO 2 can be used to switch the MVT reversibly by controlling pressure. Some other gases, such as methane, ethylene, and ethane, could also induce the MVT of the surfactant solution. A possible mechanism is proposed on the basis of the packing-parameter theory and thermodynamic principles. It is shown that the mechanism of the MVT induced by a nonpolar gas is different from the MVT induced by polar and electrolyte additives.

Cailan Yu

Papers

Rhodamine-based fluorescent sensor for mercury in buffer solution and living cells

Photoinduced Electron Storage in WO3/TiO2 Nanohybrid Material in the Presence of Oxygen and Postirradiated Reduction of Heavy Metal Ions

A Ratiometric and Targetable Fluorescent Sensor for Quantification of Mitochondrial Zinc Ions

Pathway of Oxygen Incorporation from O2 in TiO2 Photocatalytic Hydroxylation of Aromatics: Oxygen Isotope Labeling Studies

Reversible switching of a micelle-to-vesicle transition by compressed CO2.