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Quantum yield

Marissa L Weichman, Jessalyn A DeVine, Mark C Babin, Jun Li, Lifen Guo, Jianyi Ma, Hua Guo, Daniel M Neumark
The transition state governs how chemical bonds form and cleave during a chemical reaction and its direct characterization is a long-standing challenge in physical chemistry. Transition state spectroscopy experiments based on negative-ion photodetachment provide a direct probe of the vibrational structure and metastable resonances that are characteristic of the reactive surface. Dynamical resonances are extremely sensitive to the topography of the reactive surface and provide an exceptional point of comparison with theory...
October 2017: Nature Chemistry
Hujun Xie, Yang Li, Lihong Wang, Jian Kuang, Qunfang Lei, Wenjun Fang
Quantum chemistry calculations have been employed to study the mechanisms of nickel-catalyzed Suzuki-Miyaura cross-coupling reactions of benzylic carbamates with arylboronic esters, and the energy profiles have been computed to evaluate possible origins for the generation of different stereochemistry products. It has been demonstrated that the mechanism can be divided into three steps: oxidative addition, transmetallation and reduction elimination. Transmetallation is the rate-limiting step for the whole reaction cycle, and oxidative addition controls the stereoselectivity of the resulting products...
September 22, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Vladimir V Zarubaev, Tatyana C Kris'ko, Elelna V Kriukova, Tatyana D Muraviova
BACKGROUND: Among modern methods of diagnostics of tumors, the fluorescent methods are considered ones of the most prospective. Diagnostic agents (DAs) spread throughout the body by the bloodstream, so, the DA molecules are often transported by albumins and can be affected by these proteins. In our study we evaluate the effect of complex formation between bovine serum albumin (BSA) and three fluorescence DA's (Photolon, Photoditazin and Dimegin) on their fluorescent quantum yields. METHODS: Electron absorption spectroscopy and fluorescence spectroscopy were carried out to calculate fluorescence quantum yields of the DAs using Rhodamine 6G as a standard fluorescent dye...
September 18, 2017: Photodiagnosis and Photodynamic Therapy
Adewale O Adeloye, Malose J Mphahlele, Abolanle S Adekunle, Lydia Rhyman, Ponnadurai Ramasami
This study reports the synthesis and comparative investigation of the substituent effects of a new series of highly luminescent homoleptic tris-cyclometalated iridium(III) complexes of the type [Ir(N(˄)C)₃]. These are based on two ligand type derivatives comprising of 4-fluorophenylvinylquinolines and 4-methoxyphenylvinylquinolines with electron-donating and/or electron-withdrawing groups as aryl substituents at 2-position. The structures of the ligands and their complexes were characterized by means of FT-IR, UV-Vis and NMR spectrometry complemented with photoluminescence and cyclic voltammetry...
September 21, 2017: Materials
Meiting Wang, Pengfei Li, Xiangyu Jia, Wei Liu, Yihan Shao, Wenxin Hu, Jun Zheng, Bernard R Brooks, Ye Mei
The partitioning of solute molecules between immiscible solvents with significantly different polarities is of great importance. The polarization between the solute and solvent molecules plays an essential role in determining the solubility of the solute, which makes computational studies utilizing molecular mechanics (MM) rather difficult. In contrast, quantum mechanics (QM) can provide more reliable predictions. In this work, the partition coefficients of the side chain analogs of some amino acids between water and chloroform were computed...
September 21, 2017: Journal of Chemical Information and Modeling
Henrik Gustmann, Daniel Lefrancois, Andreas J Reuss, Dnyaneshwar B Gophane, Markus Braun, Andreas Dreuw, Snorri Th Sigurdsson, Josef Wachtveitl
The spin label Çm and the fluorophore Çmf are close isosteric relatives: the secondary amine Çmf can be easily oxidized to a nitroxide group to form Çm. Thus, both compounds can serve as EPR and fluorescence labels, respectively, and their high structural similarity allows direct comparison of EPR and fluorescence data, e.g. in the context of investigations of RNA conformation and dynamics. Detailed UV/vis-spectroscopic studies demonstrate that the fluorescence lifetime and the quantum yield of Çmf are directly affected by intermolecular interactions, which makes it a sensitive probe of its microenvironment...
September 21, 2017: Physical Chemistry Chemical Physics: PCCP
Jong Jin Ro, Gui Han Go, Marcus Wilhelmsson, Byeang Hyean Kim
2´-Deoxyfuranouridine derivatives presenting various aryl groups have been synthesized through Cu(I)-catalyzed intramolecular cyclizations. Moreover, corresponding pyrrolo-dC derivatives have been synthesized and both families of compounds thoroughly characterized using UV/vis and fluorescence spectroscopy as well as time-dependent density functional theory calculations. The photophysical characterization, show that our newly synthesized derivatives of the important pyrrolo-dC family have high fluorescence quantum yields and brightness values...
September 21, 2017: Methods and Applications in Fluorescence
Guangxue Feng, Jie Liu, Rongrong Liu, Duo Mao, Nikodem Tomczak, Bin Liu
Fluorescent and biocompatible organic nanoparticles have attracted great interest in cancer detection and imaging, but the nonspecific cellular uptake has limited the detection specificity and sensitivity. Herein, the authors report the ultrasmall conjugated polymer nanoparticles (CPNs) with bright far-red/near-infrared emission for targeted cancer imaging with high specificity. The sizes of the ultrasmall CPNs are around 6 nm (CPN6), while large CPNs show sizes around 30 nm (CPN30). Moreover, CPN6 exhibits largely improved fluorescence quantum yield (η) of 41% than CPN30 (25%)...
September 2017: Advanced Science (Weinheim, Baden-Wurttemberg, Germany)
Carolin M Sutter-Fella, Yanbo Li, Nicola Cefarin, Aya Buckley, Quynh Phuong Ngo, Ali Javey, Ian D Sharp, Francesca M Toma
Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH3NH3I) and methylammonium bromide (CH3NH3Br) from methylamine and the corresponding halide acid (HI or HBr)...
September 8, 2017: Journal of Visualized Experiments: JoVE
Tsung-Rong Kuo, Shih-Ting Hung, Yen-Ting Lin, Tzu-Lin Chou, Ming-Cheng Kuo, Ya-Pei Kuo, Chia-Chun Chen
Quantum dot light-emitting diodes (QD-LEDs) have been considered as potential display technologies with the characterizations of high color purity, flexibility, transparency, and cost efficiency. For the practical applications, the development of heavy-metal-free QD-LEDs from environment-friendly materials is the most important issue to reduce the impacts on human health and environmental pollution. In this work, heavy-metal-free InP/ZnS core/shell QDs with different fluorescence were prepared by green synthesis method with low cost, safe, and environment-friendly precursors...
September 19, 2017: Nanoscale Research Letters
T Papalia, A Barattucci, S Campagna, F Puntoriero, T Salerno, P Bonaccorsi
The synthesis of an efficient energy donor-acceptor system is reported, together with its photophysical properties. The bichromophoric species has been conceived to show potentialities for biological applications since a biocompatible disaccharide spacer, constituted of d-galactose and d-glucose derivatives, was used in compound 12 to connect two BODIPY units with different absorption/emission properties. The luminescence spectrum in acetonitrile of 12 shows an intense fluorescence band with a maximum at about 770 nm that is almost identical to that of the lowest-energy BODIPY, regardless of the excitation wavelength used...
September 20, 2017: Organic & Biomolecular Chemistry
Mihaela N Mocanu, Fei Yan
The interaction between chlorin e6 (Ce6) and human serum albumin (HSA) in the presence and absence of ultrasound have been investigated by ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy. Ce6 is found to bind strongly to HSA at or near physiological pH conditions, but the strength of the binding is significantly weakened at lower pHs. The intrinsic fluorescence of HSA is incrementally quenched with increasing concentration of Ce6, and the quenching is enhanced after exposure to high-frequency ultrasound...
September 13, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Ko Takase, Keiichi Noguchi, Koji Nakano
Chiral spiro polycyclic aromatic compounds with thiophene and/or thiophene S,S-dioxide units were synthesized as a new family of circularly polarized luminescence (CPL) materials. Oxidation of the thiophene unit to its S,S-dioxide provided significant changes in photophysical properties such as much higher fluorescence quantum yield and positive solvatochromism in photoluminescence spectra. Density functional theory calculations qualitatively demonstrated the observed absorption properties. The prepared chiral spiro compounds exhibit intense CPL signals with a relatively large dissymmetry factor for small organic molecules...
September 19, 2017: Organic Letters
Hongzhou Lian, Qingming Huang, Yeqing Chen, Kai Li, Sisi Liang, Mengmeng Shang, Manman Liu, Jun Lin
Narrow band red-emitting A2GeF6:Mn(4+) (A = Na, K, Rb, Cs) phosphors were prepared through a two-step precipitation-cation exchange route using a K2MnF6 precursor as the Mn(4+) source. The phase purity, morphology, and constituent were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectric spectroscopy (XPS), and electron paramagnetic resonance (EPR) examination. Optical properties were investigated by photoluminescence spectra (PL and PLE) and high-resolution PL. A temperature-dependent PL examination was performed to investigate the electron-phonon coupling emission mechanism of Mn(4+) in these alkali fluorogermanates...
September 19, 2017: Inorganic Chemistry
Meiling Zhang, Yan Zhao, Jinjun Cheng, Xiaoman Liu, Yongzhi Wang, Xin Yan, Yue Zhang, Fang Lu, Qingguo Wang, Huihua Qu
Schizonepetae Herba Carbonisata (SHC) has been used in traditional Chinese medicine (TCM) to treat haemorrhagic diseases for more than 1000 years. However, little information is available on its haemostatic components and mechanism. In this study, we developed novel water-soluble carbon dots (CDs) in aqueous extracts of SHC for the first time and a modified pyrolysis method was used to prepare the SHC using Schizonepetae Herba (SH) as the sole precursor. The SHC-CDs were characterized using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis) and fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and high-performance liquid chromatography (HPLC)...
September 19, 2017: Artificial Cells, Nanomedicine, and Biotechnology
Sushil Ranjan Bhatta, Bijan Mondal, Gonela Vijaykumar, Arunabha Thakur
A unique turn-on fluorescent device based on a ferrocene-aminonaphtholate derivative specific for Hg(2+) cation was developed. Upon binding with Hg(2+) ion, the probe shows a dramatic fluorescence enhancement (the fluorescence quantum yield increases 58-fold) along with a large red shift of 68 nm in the emission spectrum. The fluorescence enhancement with a red shift may be ascribed to the combinational effect of C═N isomerization and an extended intramolecular charge transfer (ICT) mechanism. The response was instantaneous with a detection limit of 2...
September 19, 2017: Inorganic Chemistry
Li Wang, Gang Wang, Congdi Shang, Rui Kang, Yu Fang
A naphthalimide-based low-molecular mass fluorophore (NA) was designed and synthesized by introducing an azetidine unit onto the aromatic ring of the compound as an electron-donating structure, and a hydrophilic (2-(2-aminoethylamino)ethanol) moiety into the 'N-imide site' of the core structure. UV-vis absorption and fluorescence measurements revealed that the fluorophore is soluble in water, and shows a fluorescent quantum yield of ~20% and lifetime of ~3.7 ns in the solvent within a wide pH range. Moreover, the fluorescence emission and anisotropy of the fluorophore as produced are both dependent upon the viscosity and polarity of the medium...
September 19, 2017: ACS Applied Materials & Interfaces
Thomas Müller, Crispin Reinhold, Zhaowen Dong, Jan Winkler, Henning Steinert, Marc Schmidtmann
An unusual germole-to-silole transformation is described. As key intermediates hetero-fulvenes are formed which rearrange to more stable bicyclic carbene analogues. The so-formed germylenes undergo a reductive elimination yielding elemental germanium and siloles. In contrast, the analogous silylenes are stable at ambient conditions and were identified by MS spectrometry and NMR spectroscopy supported by the results of quantum mechanical calculations. These bicyclic silylenes are stable derivatives of the global minimum of the C4Si2H6 potential energy surface...
September 19, 2017: Chemistry: a European Journal
Jie Fu, Sara Elizabeth Skrabalak
There are few methods yielding oxynitride crystals with defined shape, yet shape-controlled crystals often render enhanced photoactivity. Here, single-crystalline SrTaO2N nanoplates and polyhedra are achieved selectively. Central to these synthetic advances is the crystallization pathways used, where single-crystalline SrTaO2N nanoplates form by topotactic nitridation of aerosol-prepared Sr2Ta2O7 nanoplates and SrTaO2N polyhedra form by flux-assisted nitridation of the nanoplates. Evaluation of these materials for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) showed improved performance for the SrTaO2N nanoplates, with a record apparent quantum efficiency (AQE) of 6...
September 18, 2017: Angewandte Chemie
Nengjie Huo, Gerasimos Konstantatos
Two-dimensional transition metal dichalcogenide-based photodetectors have demonstrated potential for the next generation of 2-dimensional optoelectronics. However, to date, their sensitivity has not been superior to that of other technologies. Here we report an ultrasensitive two-dimensional photodetector employing an in-plane phototransistor with an out-of-plane vertical MoS2 p-n junction as a sensitizing scheme. The vertical built-in field is introduced for the first time in the transport channel of MoS2 phototransistors by facile chemical surface doping, which separates the photo-excited carriers efficiently and produces a photoconductive gain of >10(5) electrons per photon, external quantum efficiency greater than 10%, responsivity of 7 × 10(4) A W(-1), and a time response on the order of tens of ms...
September 18, 2017: Nature Communications
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