Upconversion luminescent materials: advances and applications.

Specific labeling of biomolecules with bright fluorophores is the keystone of fluorescence microscopy. Genetically encoded self-labeling tag proteins can be coupled to synthetic dyes inside living cells, resulting in brighter reporters than fluorescent proteins. Intracellular labeling using these techniques requires cell-permeable fluorescent ligands, however, limiting utility to a small number of classic fluorophores. Here we describe a simple structural modification that improves the brightness and photostability of dyes while preserving spectral properties and cell permeability. Inspired by molecular modeling, we replaced the N,N-dimethylamino substituents in tetramethylrhodamine with four-membered azetidine rings. This addition of two carbon atoms doubles the quantum efficiency and improves the photon yield of the dye in applications ranging from in vitro single-molecule measurements to super-resolution imaging. The novel substitution is generalizable, yielding a palette of chemical dyes with improved quantum efficiencies that spans the UV and visible range.

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A general method to improve fluorophores for live-cell and single-molecule microscopy

Luminescence techniques are among the most widely used detection methods in the life and material sciences. At the core of these methods is an ever-increasing variety of fluorescent reporters (i.e., simple dyes, fluorescent labels, probes, sensors and switches) from different fluorophore classes ranging from small organic dyes and metal ion complexes, quantum dots and upconversion nanocrystals to differently sized fluorophore-doped or fluorophore-labeled polymeric particles. A key parameter for fluorophore comparison is the fluorescence quantum yield (Φf), which is the direct measure for the efficiency of the conversion of absorbed light into emitted light. In this protocol, we describe procedures for relative and absolute determinations of Φf values of fluorophores in transparent solution using optical methods, and we address typical sources of uncertainty and fluorophore class-specific challenges. For relative determinations of Φf, the sample is analyzed using a conventional fluorescence spectrometer. For absolute determinations of Φf, a calibrated stand-alone integrating sphere setup is used. To reduce standard-related uncertainties for relative measurements, we introduce a series of eight candidate quantum yield standards for the wavelength region of ∼350-950 nm, which we have assessed with commercial and custom-designed instrumentation. With these protocols and standards, uncertainties of 5-10% can be achieved within 2 h.

Relative and absolute determination of fluorescence quantum yields of transparent samples

Transition metal complexes are of increasing interest as photosensitizers in photodynamic therapy (PDT) and, more recently, for photochemotherapy (PCT). In recent years, Ru(II) polypyridyl complexes have emerged as promising systems for both PDT and PCT. Their rich photochemical and photophysical properties derive from a variety of excited-state electronic configurations accessible with visible and near-infrared light, and these properties can be exploited for both energy- and electron-transfer processes that can yield highly potent oxygen-dependent and/or oxygen-independent photobiological activity. Selected examples highlight the use of rational design in coordination chemistry to control the lowest-energy triplet excited-state configurations for eliciting a particular type of photoreactivity for PDT and/or PCT effects. These principles are also discussed in the context of the development of TLD1433, the first Ru(II)-based photosensitizer for PDT to enter a human clinical trial. The design of TLD1433 arose from a tumor-centered approach, as part of a complete PDT package that includes the light component and the protocol for treating non-muscle invasive bladder cancer. Briefly, this review summarizes the challenges to bringing PDT into mainstream cancer therapy. It considers the chemical and photophysical solutions that transition metal complexes offer, and it puts into context the multidisciplinary effort needed to bring a new drug to clinical trial.

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Transition Metal Complexes and Photodynamic Therapy from a Tumor-Centered Approach: Challenges, Opportunities, and Highlights from the Development of TLD1433

Recently, the use of transition metal based chromophores as photo-induced single-electron transfer reagents in synthetic organic chemistry has opened up a wealth of possibilities for reinventing known reactions as well as creating new pathways to previously unattainable products. The workhorses for these efforts have been polypyridyl complexes of Ru(ii) and Ir(iii), compounds whose photophysics have been studied for decades within the inorganic community but never extensively applied to problems of interest to organic chemists. While the nexus of synthetic organic and physical-inorganic chemistries holds promise for tremendous new opportunities in both areas, a deeper appreciation of the underlying principles governing the excited-state reactivity of these charge-transfer chromophores is needed. In this Tutorial Review, we present a basic overview of the photophysics of this class of compounds with the goal of explaining the concepts, ground- and excited-state properties, as well as experimental protocols necessary to probe the kinetics and mechanisms of photo-induced electron and/or energy transfer processes.

The photophysics of photoredox catalysis: a roadmap for catalyst design

We reevaluate the absolute fluorescence and phosphorescence quantum yields of standard solutions by using a novel instrument developed for measuring the absolute emission quantum yields of solutions. The instrument consists of an integrating sphere equipped with a monochromatized Xe arc lamp as the light source and a multichannel spectrometer. By using a back-thinned CCD (BT-CCD) as the detector, the sensitivity for spectral detection in both the short and long wavelength regions is greatly improved compared with that of an optical detection system that uses a conventional photodetector. Using this instrument, we reevaluate the absolute fluorescence quantum yields (Φf) of some commonly used fluorescence standard solutions by taking into account the effect of reabsorption/reemission. The value of Φf for 5 × 10−3 M quinine bisulfate in 1 N H2SO4 is measured to be 0.52, which is in good agreement with the value (0.508) obtained by Melhuish by using a modified Vavilov method. In contrast, the value of Φf for 1.0 × 10−5 M quinine bisulfate in 1 N H2SO4, which is one of the most commonly used standards in quantum yield measurements based on the relative method, is measured to be 0.60. This value is significantly larger than Melhuish’s value (0.546), which was estimated by extrapolating the value of Φf for 5 × 10−3 M quinine bisulfate solution to infinite dilution using the self-quenching constant. The fluorescence quantum yield of 9,10-diphenylanthracene in cyclohexane is measured to be 0.97. This system can also be used to determine the phosphorescence quantum yields (Φp) of metal complexes that emit phosphorescence in the near-infrared region: the values of Φp for [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) are estimated to be 0.063 in water and 0.095 in acetonitrile under deaerated conditions at 298 K, while that in aerated water, which is frequently used as a luminescent reference in biological studies, is reevaluated to be 0.040.

Reevaluation of absolute luminescence quantum yields of standard solutions using a spectrometer with an integrating sphere and a back-thinned CCD detector.

Synthesis of ruthenium tris(2,2′-bipyridine)-type complexes tethered to peptides at 5,5′-positions

In order to establish a safety evaluation method of a steam generator of sodium-cooled fast reactors, a computer program called SERAPHIM has been developed to calculate compressible multicomponent multiphase flow with sodium-water chemical reaction under tube failure accident. In this study, a numerical model for liquid droplet entrainment from an interface of the gaseous jet and its transport was validated through the analysis of experiment on vertical discharging of high-pressure air in a water pool. This model considers the mass, momentum, and energy conservation equations including the correlation of liquid droplet entrainment velocity. The numerical result showed the entrained liquid droplet phase was accelerated by the air jet. The calculated velocity of the liquid droplet falls within the dispersion of the measured data. 

Yoshimi Shiina

Papers

Reevaluation of absolute luminescence quantum yields of standard solutions using a spectrometer with an integrating sphere and a back-thinned CCD detector.

Synthesis of ruthenium tris(2,2′-bipyridine)-type complexes tethered to peptides at 5,5′-positions

Validation of Liquid Droplet Entrainment and Transport Model in Sodium-water Reaction Analysis Code, SERAPHIM