A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single-electron-transfer (SET) processes with organic substrates upon photoexcitation with visible light.

Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2′-bipyridine) ruthenium(II), or Ru(bpy)32+ (Figure 1). These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long-lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+) that it may engage in bimolecular electron-transfer reactions in competition with deactivation pathways.3 Although these species are poor single-electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single-electron-transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.






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Figure 1


Ruthenium polypyridyl complexes: versatile visible light photocatalysts.

/pdf/visible-light-photoredox-catalysis-with-transition-metal-5d1oxrsczo.pdf

Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

/pdf/high-k-gate-dielectrics-current-status-and-materials-zjvba0c4u8.pdf

High-κ gate dielectrics: Current status and materials properties considerations

In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.

Organic Photoredox Catalysis

This Review covers recent progress on near-infrared fluorescence imaging for preclinical animal studies and clinical diagnostics and interventions.

Near-infrared fluorophores for biomedical imaging

Upconversion luminescent materials: advances and applications.

Methylmercury (MeHg+) is a strong liposoluble ion, which can be accumulated in the organs of animals and can cause prenatal nervous system and visceral damage. Therefore, the efficient and sensitive monitoring of MeHg+ in organisms is of great importance. Upconversion luminescence (UCL) detection based on rare-earth upconversion nanophosphors (UCNPs) as probes has been proved to exhibit a large anti-Stokes shift, no autofluorescence from biological samples, a remarkably deep penetration depth, and no photobleaching. In this study, a hydrophobic heptamethine cyanine dye (hCy7) modified by two long alkyl moieties and amphiphilic polymer (P-PEG)-modified nanophosphors (hCy7-UCNPs) was fabricated as a highly sensitive water-soluble probe for UCL monitoring and bioimaging of MeHg+. Further application of hCy7-UCNPs for sensing MeHg+ was confirmed by an optical titration experiment and upconversion luminescence live cell imaging. Using the ratiometric upconversion luminescence as a detection signal, which provi...

A cyanine-modified nanosystem for in vivo upconversion luminescence bioimaging of methylmercury

Lanthanide upconversion nanophosphors (UCNPs) show unique upconversion luminescence where lower-energy photons (such as near-infrared (NIR) excitation) are converted into higher-energy photons covering the NIR to the UV region, and are considered to have a bright future in clinical translation. As UCNPs are used in a significant number of potential bio-applications, their biosafety is important and has attracted significant attention. In this critical review, recent reports regarding the cellular internalization, biodistribution, excretion, cytotoxicity and in vivo toxic effects of UCNPs are reviewed. In particular, the studies which evaluated the association between the chemical and physical properties of UCNPs and their biodistribution, excretion, and toxic effects are presented in detail. Finally, we also discuss the challenges of ensuring the biosafety of UCNPs in vivo.

The biosafety of lanthanide upconversion nanomaterials

ConspectusResonance energy transfer (RET) describes the process that energy is transferred from an excited donor to an acceptor molecule, leading to a reduction in the fluorescence emission intensity of the donor and an increase in that of the acceptor. By this technique, measurements with the good sensitivity can be made about distance within 1 to 10 nm under physiological conditions. For this reason, the RET technique has been widely used in polymer science, biochemistry, and structural biology. Recently, a number of RET systems incorporated with nanoparticles, such as quantum dots, gold nanoparticles, and upconversion nanoparticles, have been developed. These nanocrystals retain their optical superiority and can act as either a donor or a quencher, thereby enhancing the performance of RET systems and providing more opportunities in excitation wavelength selection.Notably, lanthanide-doped upconversion nanophosphors (UCNPs) have attracted considerable attention due to their inherent advantages of large ...

Resonance Energy Transfer in Upconversion Nanoplatforms for Selective Biodetection.

Temperature is an essential factor that counts for living systems where complicated vital activities are usually temperature dependent. In vivo temperature mapping based on non-contact optical approach will be beneficial for revealing the physiological phenomena behind with minimized influence to the organism. Herein, a highly thermal-sensitive upconversion system based on triplet–triplet annihilation (TTA) mechanism is pioneered to indicate body temperature variation sensitively over the physiological temperature range. The temperature-insensitive NaYF4: Nd nanophosphors with NIR emission was incorporated into the temperature-responsive TTA-upconversion system to serve as an internal calibration unit. Consequently, a ratiometric thermometer capable of accurately monitoring the temperature changes in vivo was developed with high thermal sensitivity (~7.1% K−1) and resolution (~0.1 K). Though luminescence imaging is a promising approach for contactless thermometry in vivo, the low thermal sensitivity of existing thermometers limits its potential. Here, the authors develop a high-sensitivity ratiometric nanothermometer based on triplet-sensitized upconversion.

/pdf/ratiometric-nanothermometer-in-vivo-based-on-triplet-59u827ficl.pdf

Wei Feng

Papers

Upconversion luminescent materials: advances and applications.

A cyanine-modified nanosystem for in vivo upconversion luminescence bioimaging of methylmercury

The biosafety of lanthanide upconversion nanomaterials

Resonance Energy Transfer in Upconversion Nanoplatforms for Selective Biodetection.

Ratiometric nanothermometer in vivo based on triplet sensitized upconversion