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Quantum yield

Gustavo A Saenz, Goran Karapetrov, James Curtis, Anupama B Kaul
The design, fabrication, and characterization of ultra-high responsivity photodetectors based on mesoscopic multilayer MoS2 is presented, which is a less explored system compared to direct band gap monolayer MoS2 that has received increasing attention in recent years. The device architecture is comprised of a metal-semiconductor-metal (MSM) photodetector, where Mo was used as the contact metal to suspended MoS2 membranes. The photoresponsivity [Formula: see text] was measured to be ~1.4 × 104 A/W, which is > 104 times higher compared to prior reports, while the detectivity D* was computed to be ~2...
January 19, 2018: Scientific Reports
Marsel Z Shafikov, Alfiya Suleymanova, Alexander Schinabeck, Hartmut Yersin
The di-nuclear Ag(I) complex has been designed to show thermally activated delayed fluorescence (TADF) оf high efficiency. Strongly electron-donating terminal ligands are introduced to destabilize the d-orbitals of the Ag+ ions. Consequently, the orbitals distinctly contribute to the HOMO, whereas the LUMO is localized on the bridging ligand. This ensures charge transfer character of the lowest excited singlet S1 and triplet T1 state. Accordingly, a small energy gap ΔE(S1─T1) is obtained, being essential for TADF behavior...
January 19, 2018: Journal of Physical Chemistry Letters
Xiaoyu Zhao, Xiaoyu Song, Yang Li, Ze Chang, Long Chen
Metal-organic frameworks (MOFs) have emerged as promising light-harvesting platforms for energy transfer materials. However, the targeted construction of MOFs with desirable photophysical properties and pore structures is still a challenge. Herein, 1,1,2,2-tetrakis(4-(pyridin-4-yl) phenyl)ethene (tppe) is selected as ligand for the construction of light-harvesting MOFs due to its highly emissive and rigid backbone, which could benefit the light-harvesting performance of the MOFs. Three MOFs (MOFs 1-3) were obtained based on different metal centers (Zn2+ and Cd2+) and carboxylate building blocks...
January 19, 2018: ACS Applied Materials & Interfaces
Gang Wang, Qinglei Guo, Da Chen, Zhiduo Liu, Xiaohu Zheng, Anli Xu, Siwei Yang, Guqiao Ding
Recently, the biomass "bottom-up" approach for the synthesis of graphene quantum dots have attracted broad interest because of the outstanding features, including low-cost, rapid and environmentally friendly nature. However, the low crystalline quality of products, substitutional doping with heteroatoms in lattice and ambiguous reaction mechanism strongly challenge the further development of this technique. Herein, we proposed a facile and effective strategy to prepare controllable sulfur (S) doping in graphene quantum dots, occurring in a lattice substitution manner, by hydrothermal treatment of durian with platinum catalyst...
January 19, 2018: ACS Applied Materials & Interfaces
Ryota Yamano, Yu Shibata, Ken Tanaka
Dibenzo[7]helicenes were synthesized with up to 99% ee via the rhodium(I)/binap complex-catalyzed enantioselective intramolecular [2+2+2] cycloaddition of 2-phenylnaphthalene-linked tryines. Additionally, [2+1+2+1] cycloaddition products, twisted anthracenes, were also synthesized by using difluorphos as a ligand. Although this compound is not configurationally stable at elevated temperature, the Scholl reaction of which afforded a configurationally stable double dibenzo[6]helicene. The thus obtained dibenzo[7]helicene exhibited good circularly polarized luminescence property and the double dibenzo[6]helicene exhibited high fluorescence quantum yield...
January 18, 2018: Chemistry: a European Journal
Henrique Vieira Rivera Vila, Luiz Antônio Ribeiro, Luiz Guilherme Machado de Macedo, Ricardo Gargano
A thorough time-independent quantum scattering study is performed on a benchmark potential energy surface for the H+Li2 reaction at the fundamental electronic state. Integral and differential cross sections are calculated along with thermal rate coefficients until convergence is reached. Our findings show that vibrational and rotational excitations of the reactant hinder reactivity, though for the latter a considerable reaction promotion was spotted as we increase the reactant rotational quantum number until the critical value of j = 4...
January 18, 2018: Scientific Reports
Haifang Liu, Zhaohui Li, Yuanqiang Sun, Xin Geng, Yalei Hu, Hongmin Meng, Jia Ge, Lingbo Qu
Carbon dots (CDs) have a wide range of applications in chemical, physical and biomedical research fields. We are particularly interested in the use of CDs as fluorescence nanomaterials for targeted tumor cell imaging. One of the important aspects of success is to enhance the fluorescence quantum yields (QY) of CDs as well as increase their targetability to tumor cells. However, most of the reported CDs are limited by relative low QY. In the current study, for the first time, one-step synthesis of highly luminescent CDs by using folic acid (FA) as single precursor was obtained in natural water through hydrothermal method...
January 18, 2018: Scientific Reports
Jason K Gurchiek, Han Bao, Maria Agustina Domínguez-Martín, Sarah E McGovern, Claire E Marquardt, Jerome D Roscioli, Soumen Ghosh, Cheryl A Kerfeld, Warren F Beck
The Orange Carotenoid Protein (OCP) mediates nonphotochemical quenching (NPQ) mechanisms in cyanobacteria. A bound ketocarotenoid serves as a sensor of mid-visible light intensity and as a quencher of phycocyanobilin excitons in the phycobilisome. The photochemical mechanism that triggers conversion of the protein from a resting, orange state (OCPO) to an active, red state (OCPR) after optical preparation of the S2 state of the carotenoid remains an open question. We report here that the fluorescence spectrum and quantum yield of the bound carotenoids in OCPO report important details of the motions that follow optical preparation of the S2 state...
January 18, 2018: Journal of Physical Chemistry. B
H De Raedt, F Jin, M I Katsnelson, K Michielsen
It is shown that by fitting a Markovian quantum master equation to the numerical solution of the time-dependent Schrödinger equation of a system of two spin-1/2 particles interacting with a bath of up to 34 spin-1/2 particles, the former can describe the dynamics of the two-spin system rather well. The fitting procedure that yields this Markovian quantum master equation accounts for all non-Markovian effects in as much the general structure of this equation allows and yields a description that is incompatible with the Lindblad equation...
November 2017: Physical Review. E
Akhilesh Pandey, Avanish Kumar, Sanjay Puri
Dyson demonstrated an equivalence between infinite-range Coulomb gas models and classical random matrix ensembles for the study of eigenvalue statistics. We introduce finite-range Coulomb gas (FRCG) models via a Brownian matrix process, and study them analytically and by Monte Carlo simulations. These models yield new universality classes, and provide a theoretical framework for the study of banded random matrices (BRMs) and quantum kicked rotors (QKRs). We demonstrate that, for a BRM of bandwidth b and a QKR of chaos parameter α, the appropriate FRCG model has the effective range d=b^{2}/N=α^{2}/N, for large N matrix dimensionality...
November 2017: Physical Review. E
Juan D Jaramillo, Jiawen Deng, Jiangbin Gong
A result of great theoretical and experimental interest, the Jarzynski equality predicts a free energy change ΔF of a system at inverse temperature β from an ensemble average of nonequilibrium exponential work, i.e., 〈e^{-βW}〉=e^{-βΔF}. The number of experimental work values needed to reach a given accuracy of ΔF is determined by the variance of e^{-βW}, denoted var(e^{-βW}). We discover in this work that var(e^{-βW}) in both harmonic and anharmonic Hamiltonian systems can systematically diverge in nonadiabatic work protocols, even when the adiabatic protocols do not suffer from such divergence...
October 2017: Physical Review. E
Raam Uzdin
The Clausius inequality form of the second law of thermodynamics relates information changes (entropy) to changes in the first moment of the energy (heat and indirectly also work). Are there similar relations between other moments of the energy distribution, and other information measures, or is the Clausius inequality a one of a kind instance of the energy-information paradigm? If there are additional relations, can they be used to make predictions on measurable quantities? Changes in the energy distribution beyond the first moment (average heat or work) are especially important in small systems which are often very far from thermal equilibrium...
September 2017: Physical Review. E
N Leibovich, E Barkai
We demonstrate that the measurement of 1/f^{α} noise at the single molecule or nano-object limit is remarkably distinct from the macroscopic measurement over a large sample. The single-particle measurements yield a conditional time-dependent spectrum. However, the number of units fluctuating on the time scale of the experiment is increasing in such a way that the macroscopic measurements appear perfectly stationary. The single-particle power spectrum is a conditional spectrum, in the sense that we must make a distinction between idler and nonidler units on the time scale of the experiment...
September 2017: Physical Review. E
Kaiyu Wang, Yuqing Huang, Pieter E S Smith, Zhiyong Zhang, Shuhui Cai, Zhong Chen
OBJECTIVE: A method is proposed to obtain high-resolution 2-D -resolved nuclear magnetic resonance (NMR) spectra in inhomogeneous magnetic fields. METHODS: The proposed experiment enables the acquisition of an entire 2-D spectrum in a single scan by utilizing intermolecular double-quantum coherences and the spatial encoding of NMR observables. RESULTS: Chemical shifts, coupling constants, and multiplet patterns are recovered even when field inhomogeneities are severe enough to completely obscure conventional NMR spectra...
February 2018: IEEE Transactions on Bio-medical Engineering
Kifle Z Aregahegn, Michael J Ezell, Barbara J Finlayson-Pitts
The environmental fates of nitenpyram (NPM), a widely used neonicotinoid insecticide, are not well known. A thin solid film of NPM deposited on a germanium attenuated total reflectance (ATR) crystal was exposed to radiation from a low-pressure mercury lamp at 254 nm, or from broadband low pressure mercury photolysis lamps centered at 350 or 313 nm. The loss during photolysis was followed in time using FTIR. The photolysis quantum yields (), defined as the number of NPM molecules lost per photon absorbed, were determined to be (9...
January 18, 2018: Environmental Science & Technology
Prabhat K Upadhyay, Sreekar B Marpu, Erin N Benton, Corshai L Williams, Ameya Telang, Mohammad A Omary
We report a phosphorescent chemosensor based on a trinuclear Au(I) pyrazolate complex or [Au(3-CH3,5-COOH)Pz]3, (aka Au3Pz3) stabilized in aqueous chitosan (CS) polymer media. Au3Pz3 is synthesized in situ within aqueous CS media at pH ~ 6.5 and room temperature (RT). Au3Pz3 exhibits strong red emission (λmax ~690 nm) in such solutions. The Au3Pz3 emission is found to be sensitive to sub-ppm/nM levels of silver ions. On addition of silver salt to Au3Pz3/CS aqueous media, a bright-green emissive adduct (Au3Pz3/Ag+) with peak maximum within 475-515 nm is developed...
January 17, 2018: Analytical Chemistry
Piotr Cmoch, Piotr Krzeczyński, Andrzej Leś
The molecular structure of capecitabine (a widely applied prodrug of 5-fluorouracil) was studied by multinuclear NMR measurements and DFT quantum mechanical calculations. One or two tautomeric forms in a solution were detected depending on the solvent used. In the organic solvents, a mixture of two forms of capecitabine was observed: carbamate and imine tautomers. In the aqueous solution, only the carbamate form was found. The methylation of capecitabine yields mainly two products in different proportions: N³-methylcapecitabine and N⁷-methylcapecitabine...
January 13, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Xiaoyi Sun, Lele Zhao, Xiao Han, Hui Liu, Yu Gao, Yanchun Tao, Haiquan Zhang, Bing Yang, Ping Lu
Creation of organic luminescent materials with high solid-state efficiency is of vital importance for their applications in optoelectronic fields. Here, a series of AIE luminogens (AIE gens), (Z)-2,3-bis(4-(9,9-bis(6-(9H-carbazol-9-yl)hexyl)-9H-fluoren-2-yl)phenyl)-3-phenylacrylonitrile (SFC), and 2,3-bis(4-(9,9-bis(6-(9H-carbazol-9-yl)hexyl)-9H-fluoren-2-yl)phenyl)fumaronitrile (DFC), utilizing 2,3,3-triphenylacrylonitrile and 2,3-diphenylfumaronitrile as respective centers, are designed and synthesized by Suzuki coupling reactions with high yields...
January 17, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Timothy Proctor, Kenneth Rudinger, Kevin Young, Mohan Sarovar, Robin Blume-Kohout
Randomized benchmarking (RB) is widely used to measure an error rate of a set of quantum gates, by performing random circuits that would do nothing if the gates were perfect. In the limit of no finite-sampling error, the exponential decay rate of the observable survival probabilities, versus circuit length, yields a single error metric r. For Clifford gates with arbitrary small errors described by process matrices, r was believed to reliably correspond to the mean, over all Clifford gates, of the average gate infidelity between the imperfect gates and their ideal counterparts...
September 29, 2017: Physical Review Letters
Joji Nasu, Junki Yoshitake, Yukitoshi Motome
In conventional insulating magnets, heat is carried by magnons and phonons. In contrast, when the magnets harbor a quantum spin liquid state, emergent quasiparticles from the fractionalization of quantum spins can carry heat. Here, we investigate unconventional thermal transport yielded by such exotic carriers, in both longitudinal and transverse components, for the Kitaev model, whose ground state is exactly shown to be a quantum spin liquid with fractional excitations described as itinerant Majorana fermions and localized Z_{2} fluxes...
September 22, 2017: Physical Review Letters
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