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Principles Of Fluorescence Spectroscopy

The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

An overview of N-heterocyclic carbenes

Organic reactions that involve the direct functionalization of non-activated C–H bonds represent an attractive class of transformations which maximize atom- and step-economy, and simplify chemical synthesis. Due to the high stability of C–H bonds, these processes, however, have most often required harsh reaction conditions, which has drastically limited their use as tools for the synthesis of complex organic molecules. Following the increased understanding of mechanistic aspects of C–H activation gained over recent years, great strides have been taken to design and develop new protocols that proceed efficiently under mild conditions and duly benefit from improved functional group tolerance and selectivity. In this review, we present the current state of the art in this field and detail C–H activation transformations reported since 2011 that proceed either at or below ambient temperature, in the absence of strongly acidic or basic additives or without strong oxidants. Furthermore, by identifying and discussing the major strategies that have led to these improvements, we hope that this review will serve as a useful conceptual overview and inspire the next generation of mild C–H transformations.

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Mild metal-catalyzed C–H activation: examples and concepts

Supramolecular Chirality in Self-Assembled Systems

Fluorine has received great attention in all fields of science. “Small atom with a big ego” was the title of the Symposium at the ACS meeting in San Francisco in 2000, where a number of the current scientific and industrial aspects of fluorine chemistry made possible by the small size and high electronegativity of the atom were discussed. This small atom has provided mankind with significant benefits in special products such as poly(tetrafluroethylene) (PTFE), freon, fluoro-liquid crystals, optical fiber, pharmaceutical and agrochemical compounds, and so on, all of which have their own unique properties that are otherwise difficult to obtain.1 For instance, at present, up to 30% of agrochemicals and 10% of pharmaceuticals currently used contain fluorine atoms. Therefore, organic fluorine compounds have received a great deal of interest and attention from the scientists involved in diverse fields of science and technology. Now, not only C-F bond formation but also selective C-F bond activation have become current subjects of active investigation from the viewpoint of effective synthesis of fluoroorganic compounds. The former is highlighted by designing a sophisticated fluorinating reagent for regioand stereocontrolled fluorination and developing versatile multifunctional and easily prepared building blocks. C-F bond formation has been treated extensively in several reviews2 and books.3 The latter is a subject that has been less explored but would be promising for selective defluorination of aliphatic fluorides, cross-coupling with aryl fluorides, and * To whom correspondence should be addressed. Phone: 81-78-803-5799. Fax: 81-78-803-5799. E-mail: amii@kobe-u.ac.jp and uneyamak@cc.okayamau.ac.jp. † Kobe University. ‡ Okayama University. Chem. Rev. 2009, 109, 2119–2183 2119

C-F bond activation in organic synthesis.

Chiroptical spectroscopies, such as electronic circular dichroism (ECD) and vibrational circular dichroism (VCD), are highly sensitive techniques to probe molecular conformation, configuration, solvation, and aggregation. Here we report the application of these techniques to study the fungal metabolite brevianamide B. Comparison of the experimental ECD and VCD spectra with the density functional theory simulated counterparts establishes that VCD is the more reliable technique to assign absolute configuration due to the larger functional and dispersion dependence of computed ECD spectra. Despite a low amount of available material and a relatively unusual example of using VCD carbonyl multiplets, the absolute configuration could be reliably predicted, strengthening the case for application of VCD in the study of complex natural products. Spectral and crystallographic evidence for or against the formation of a dimeric aggregate is discussed; in solution, the VCD spectra strongly suggest only monomeric specie...

https://biblio.ugent.be/publication/5952071/file/5952081.pdf

Chiroptical studies on brevianamide B: vibrational and electronic circular dichroism confronted.

Differentially substituted Cr(CO)3-complexed aryl pyridines have been shown to readily undergo stoichiometric palladation and subsequent arylation using boronic acid nucleophiles. The positioning of the aryl substituents has been shown to be key in governing substrate reactivity, whereby sterically congested compounds prevent the geometry required for cyclometallation.

Stoichiometric C–H arylation of tricarbonyl(arene)chromium complexes bearing pyridine directing groups

The elucidation of protein/drug interactions remains a major challenge in drug discovery. Liquid chromatography–tandem mass spectrometry has emerged as a tremendously powerful technology for this e...

/pdf/unbiased-mass-spectrometry-elucidation-of-the-targets-and-3duak93cyi.pdf

Unbiased Mass Spectrometry Elucidation of the Targets and Mechanisms of Activity-Based Probes: A Case Study Involving Sulfonyl Fluorides

1,8-Diarylnaphthalenes show interesting potential as chiral sensors, environment sensors and stereodynamic switches. The kinetics and thermodynamics of the conformational equilibria of two such compounds are described. These compounds, along with others reported previously, show that several features can be used to tune the conformational behaviour of these compounds, giving the possibility to design molecules for specific applications in the future.

ortho-Substituted 1,8-Diarylnaphthalenes: Conformational Thermodynamics and Kinetics

Tuning halide composition in perovskites is a powerful approach demonstrated to enhance the performance of perovskite photovoltaic devices where such compositional modifications drive improvements in open‐circuit voltage (Voc) and a reduction in nonradiative voltage losses. Similarly, photodetectors (PDs) operate as light to current conversion devices hence it is relevant to investigate whether performance enhancements can be achieved by similar strategies. Herein, perovskite PDs are fabricated with an inverted photodiode configuration based on a MAPb(I1‐xBrx)3 perovskite (MA = methylammonium) active layer over the x = 0–0.25 composition range. Interestingly, it has been found that increasing the Br content up to 0.15 (15%) leads to a significant reduction in dark current (Jd), with values as low as 1.3 × 10−9 A cm−2 being achieved alongside a specific detectivity of 8.7 × 1012 Jones. Significantly, it has been observed an exponential relationship between the Jd of devices and their Voc over the 0–15% Br range. The superior performances of the 15% Br‐containing devices are attributed to the reduction of trap states, a better charge extraction of photogenerated carriers, and an improvement in photoactive layer morphology and crystallinity.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/adom.202201816

Matthew J. Fuchter

Papers

Chiroptical studies on brevianamide B: vibrational and electronic circular dichroism confronted.

Stoichiometric C–H arylation of tricarbonyl(arene)chromium complexes bearing pyridine directing groups

Unbiased Mass Spectrometry Elucidation of the Targets and Mechanisms of Activity-Based Probes: A Case Study Involving Sulfonyl Fluorides

ortho-Substituted 1,8-Diarylnaphthalenes: Conformational Thermodynamics and Kinetics

Tuning Halide Composition Allows Low Dark Current Perovskite Photodetectors With High Specific Detectivity