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Quantum yield

Franziska Krieg, Stefan T Ochsenbein, Sergii Yakunin, Stephanie Ten Brinck, Philipp Aellen, Adrian Süess, Baptiste Clerc, Dominic Guggisberg, Olga Nazarenko, Yevhen Shynkarenko, Sudhir Kumar, Chih-Jen Shih, Ivan Infante, Maksym V Kovalenko
Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules such as 3-( N , N -dimethyloctadecylammonio)propanesulfonate, resulting in much improved chemical durability...
March 9, 2018: ACS Energy Letters
Luis Angel Martínez-Martínez, Matthew Du, Raphael Florentino Ribeiro, Stéphane Kéna-Cohen, Joel Yuen-Zhou
Singlet fission is an important candidate to increase energy conversion efficiency in organic pho- tovoltaics; it provides a pathway to increase the quantum yield of excitons per photon absorbed in select materials. We investigate the dependence of exciton quantum yield for acenes in the strong light-matter interaction (polariton) regime, where the materials are embedded in optical microcavi- ties. Starting from an open-quantum-systems approach, we build a kinetic model for time-evolution of species of interest in the presence of quenchers and show that polaritons can decrease or increase exciton quantum yields compared to the cavity-free case...
March 18, 2018: Journal of Physical Chemistry Letters
Chan Wang, Tantan Hu, Zhuoqi Wen, Jingdan Zhou, Xioajie Wang, Qian Wu, Chuanxi Wang
Nitrogen doping can effectly adjust the compositions and structures of carbon dots and hence enhance their fluorescence. In this work, we report a fast and low-cost route for synthesis of nitrogen-doped carbon dots (N-CDs) by microwave pyrolysis of citric acid and ammonium within 7 min. The as-prepared N-CDs contain plentiful oxygen and nitrogen functional groups, and dispaly intense fluorescence with high quantum yield of ca. 44.3% and have an average size of 1.8 nm. The obtained N-CDs exhibit highly stable against photobleaching, ionic strengths, and can be used for selective and sensitive detection of Fe(III)...
March 8, 2018: Journal of Colloid and Interface Science
Daniel Amgar, Tal Binyamin, Vladimir Uvarov, Lioz Etgar
One of the most attractive features of perovskite materials is their chemical flexibility. Due to innovative chemical compositions of perovskites, their optical and structural properties, and functionalities have become more advanced, enabling better solar performance in photovoltaics, as well as robustness and excellent properties in the nanoscale for optoelectronics. The quest for novel perovskite compositions in the nano-scale is significantly important. This paper reports on a mixed-cation system of RbxCs1-xPbX3 (where X = Cl or Br) nanoparticles...
March 16, 2018: Nanoscale
Matthew S Church, Timothy J H Hele, Gregory S Ezra, Nandini Ananth
We extend the Mixed Quantum-Classical Initial Value Representation (MQC-IVR), a semiclassical method for computing real-time correlation functions, to electronically nonadiabatic systems using the Meyer-Miller-Stock-Thoss (MMST) Hamiltonian in order to treat electronic and nuclear degrees of freedom (dofs) within a consistent dynamic framework. We introduce an efficient symplectic integration scheme, the MInt algorithm, for numerical time evolution of the phase space variables and monodromy matrix under the non-separable MMST Hamiltonian...
March 14, 2018: Journal of Chemical Physics
Xuecheng Tao, Philip Shushkov, Thomas F Miller
We describe a path-integral approach for including nuclear quantum effects in non-adiabatic chemical dynamics simulations. For a general physical system with multiple electronic energy levels, a corresponding isomorphic Hamiltonian is introduced such that Boltzmann sampling of the isomorphic Hamiltonian with classical nuclear degrees of freedom yields the exact quantum Boltzmann distribution for the original physical system. In the limit of a single electronic energy level, the isomorphic Hamiltonian reduces to the familiar cases of either ring polymer molecular dynamics (RPMD) or centroid molecular dynamics Hamiltonians, depending on the implementation...
March 14, 2018: Journal of Chemical Physics
Minah Han, Byeongjoon Kim, Jongduk Baek
We investigate the detectability of breast cone beam computed tomography images using human and model observers and the variations of exponent, β, of the inverse power-law spectrum for various reconstruction filters and interpolation methods in the Feldkamp-Davis-Kress (FDK) reconstruction. Using computer simulation, a breast volume with a 50% volume glandular fraction and a 2mm diameter lesion are generated and projection data are acquired. In the FDK reconstruction, projection data are apodized using one of three reconstruction filters; Hanning, Shepp-Logan, or Ram-Lak, and back-projection is performed with and without Fourier interpolation...
2018: PloS One
Niels Vandenberk, Anders Barth, Doortje Borrenberghs, Johan Hofkens, Jelle Hendrix
Förster resonance energy transfer (FRET) is a powerful tool to probe molecular interactions, activity, analytes, forces and structure. Single-molecule (sm) FRET additionally allows real-time quantifications of conformation and conformational dynamics. SmFRET robustness critically depends on the employed dyes, yet a systematic comparison of different dye pairs is lacking. Here, we evaluated blue (Atto488 and Alexa488) and far-red (Atto647N, Alexa647, StarRed and Atto655) dyes using confocal smFRET spectroscopy on freely diffusing dsDNA molecules...
March 15, 2018: Journal of Physical Chemistry. B
Matthew P Kroonblawd, Fabio Pietrucci, Antonino Marco Saitta, Nir Goldman
We demonstrate the capability of creating robust density functional tight binding (DFTB) models for chemical reactivity in prebiotic mixtures through force matching to short time scale quantum free energy estimates. Molecular dynamics using density functional theory (DFT) is a highly accurate approach to generate free energy surfaces for chemical reactions, but the extreme computational cost often limits the time scales and range of thermodynamic states that can feasibly be studied. In contrast, DFTB is a semi-empirical quantum method that affords up to a thousandfold reduction in cost and can recover DFT-level accuracy...
March 15, 2018: Journal of Chemical Theory and Computation
Jun Zhang, Alexander Sandberg, Audun Konsmo, Xiongyu Wu, Sofie Nyström, K Peter Nilsson, Peter Konradsson, Harry LeVine, Mikael Lindgren, Per Hammarström
We revisited the Congo red analogue 2,5-bis(4'-hydroxy-3'-carboxy-styryl)benzene (X-34) to develop this highly fluorescent amyloid dye for imaging Alzheimer's disease (AD) pathology comprising Aβ and Tau fibrils. A selection of ligands with distinct optical properties were synthesized by replacing the central benzene unit of X-34, with other heterocyclic moieties. Full photophysical characterization was performed determining absorbance and fluorescence spectra, Stokes shift, quantum yield and fluorescence lifetimes...
March 15, 2018: Chemistry: a European Journal
Claus Hierlinger, David B Cordes, Alexandra M Z Slawin, Denis Jacquemin, Véronique Guerchais, Eli Zysman-Colman
This study concerns an assessment of the impact of the interruption of the electronic crosstalk between the pyridine rings in the ancillary ligand on the photoluminescence properties of the corresponding iridium(iii) complexes. Two new cationic Ir(iii) complexes, [Ir(dFmesppy)2 (pmdp)]PF6 , 1, and [Ir(mesppy)2 (pmdp)]PF6 , 2, [where dFmesppy is 2-(2,4-difluorophenyl)-4-mesitylpyridinato, mesppy is 4-mesityl-2-phenylpyridinato and pmdp is 2,2'-(phenylmethine)dipyridine, L1] possessing sterically congested cyclometalating ligands combined with the nonconjugated diimine ancillary N^N ligand are reported and their solution-state and thin film photophysical properties analyzed by both experimental and theoretical methods...
March 15, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Guilin Wu, Shaowei Jiang, Hui Liu, Shidan Zhu, Duoduo Zhou, Ying Zhang, Qi Luo, Jun Li
In riparian zones along the Tarim River in northeastern China, the co-dominance by Populus euphratica and Tamarix ramosissima at the early succession stage shifts to P. euphratica dominance in the late stages. However, little is known about how this shift is mediated by the highly variable water conditions in riparian zones. Here we conducted a mesocosm experiment in which we measured the physiological and morphological traits of these two co-occuring species grown in mixtures under simulated favorable groundwater condition and no groundwater availability...
March 14, 2018: Scientific Reports
Christoph Helling, Christoph Wölper, Stephan Schulz
Cp*AsCl2 (Cp* = C5Me5) reacts with one equivalent of LGa (L = HC[C(Me)N(2,6-i-Pr2C6H3)]2) with formation of L(Cl)GaAs(Cl)Cp* 1, whereas the reaction with two equivalents of LGa yielded gallaarsene LGaAsCp* 2 containing a Ga=As double bond and (η1-Ga(Cp*)L(η2-GaL)(μ-As3) 3. 2 and 3 were structural-ly characterized by single crystal X-ray diffraction and the π-bonding contribution in 2 was analyzed by temperature-dependent 1H NMR spectroscopy (9.65 kcal mol-1) and by quantum mechani-cal computation.
March 14, 2018: Journal of the American Chemical Society
Miguel A Esteruelas, Ana M López, Enrique Oñate, Ainhoa San-Torcuato, Jui-Yi Tsai, Chuanjun Xia
The preparation and photophysical properties of heteroleptic iridium(III) complexes containing a dianionic C,C,C,C-tetradentate ligand and a cyclometalated phenylpyridine group are described. Complex [Ir(μ-OMe)(COD)]2 (1, COD = 1,5-cyclooctadiene) reacts with 1,1-diphenyl-3,3-butylenediimidazolium iodide ([PhIm(CH2 )4 ImPh]I2 ), in the presence NaOt Bu, to give [Ir(μ-I){κ4 - C, C, C, C-[C6 H4 Im(CH2 )4 ImC6 H4 ]}]2 (2), which leads to {[Ir{κ4 - C, C, C, C-[C6 H4 Im(CH2 )4 ImC6 H4 ]}]2 (μ-OH)(μ-OMe)} (3) by treatment first with silver trifluoromethanesulfonate (AgOTf) in acetone-dichloromethane and subsequently with KOH in methanol...
March 14, 2018: Inorganic Chemistry
Luca Malfatti, Plinio Innocenzi
Carbon dots are an emerging class of carbon-based nanostructures produced by low-cost raw materials which exhibit a widely-tunable photoluminescence and a high quantum yield. The potential of these nanomaterials as a substitute of semiconductor quantum dots in optoelectronics and biomedicine is very high, however they need a customized chemistry to be integrated in host-guest systems or functionalized in core-shell structures. This review is focused on recent advances of the sol-gel chemistry applied to the C-dots technology...
March 14, 2018: Chemical Record: An Official Publication of the Chemical Society of Japan ... [et Al.]
Shuang Yang, Feng Zhang, Jia Tai, Yang Li, Yang Yang, Hui Wang, Jianxu Zhang, Zhigang Xie, Bin Xu, Haizheng Zhong, Kun Liu, Bai Yang
Perovskite quantum dots (PQDs) exhibit remarkable photoluminescence properties; however, their use in biological applications is hindered by their extreme sensitivity to water. We report a facile and general strategy for the preparation of aqueous colloidally stable polystyrene-b-poly(ethyl oxide) (PS-b-PEO) grafted MAPbBr3 QDs (MA = methylammonium): transferring the as-synthesized PQD@PS-b-PEO from toluene into water using precipitation in hexane as a critical intermediate step. When rehydrating the precipitate in water, the PQDs can be dispersed well individually or self-assembled into well-defined vesicular nanostructures with high photoluminescence quantum yields of up to 43%, high color purity (full width at half maximum down to 18 nm), and long average photoluminescence lifetimes up to 164 ns...
March 14, 2018: Nanoscale
L Basso, F Gorrini, M Cazzanelli, N Bazzanella, A Bifone, A Miotello
Nanodiamonds (NDs) containing negatively charged Nitrogen-Vacancy (NV) centers are promising materials for applications in photonics, quantum computing, and sensing of environmental parameters like temperature, strain and magnetic fields. However, the production of fluorescent NDs remains a technological challenge, requiring a complex multi-step process involving controlled introduction of substitutional nitrogen into the diamond lattice, annealing and fragmentation from macrocrystals to nanocrystals. Here, we report on a single-step, all-optical process for the production of nanometric-sized fluorescent diamonds based on laser ablation of a carbon substrate at low temperature (100 °C) under a nitrogen atmosphere...
March 14, 2018: Nanoscale
Daiki Kato, Hayato Sakai, Yasuyuki Araki, Takehiko Wada, Nikolai V Tkachenko, Taku Hasobe
Photophysical control and switching on organic-inorganic hybrid interfaces are of great interest in diverse fundamental and applicative research areas. 6,13-Bis(triisopropylsilylethynyl)pentacene (TP) is well-known to exhibit efficient singlet fission (SF) for generation of high-yield triplet excited states in aggregated forms, whereas perylenediimide (PDI) ensembles show the characteristic excimer formation. Additionally, a combination of pentacene (electron donor: D) and PDI (electron acceptor: A) is expected to undergo an efficient photoinduced electron transfer (PET), and absorption of two chromophores combined covers the entire visible region...
March 14, 2018: Physical Chemistry Chemical Physics: PCCP
N N Subrahmanyeswara Rao, Parag A Deshpande
Computational investigation of orotate phosphoribosyltransferase (OPRT) action, an enzymatic reaction between phosphoribosyl pyrophosphate (PRPP) and orotic acid (OA) to yield orotidine 5'-monophosphate (OMP), was carried out. Insights into the pathways of the substrate attack step of the reaction were developed under the quantum mechanics/molecular mechanics framework with S. cerevisiae strain as the representative enzyme bearer. Four pathways were proposed for PRPP and OA binding differing in the sequence of PRPP, OA and Mg2+ ion complexation with OPRT...
February 24, 2018: Computational Biology and Chemistry
Leon Buschbeck, Jens Christoffers
The 2,5-diaminoterephthalate structural motif is a powerful chromophore with remarkable fluorescence properties. Containing two carboxylate and two amino functions it defines a colored molecular scaffold which allows for orthogonal functionalization with different functional units. Therefore, different applications in Life Sciences and Materials Science could be addressed. In this study, the two amino functions were alkylated by reductive amination with side chains carrying amino (orthogonally protected as Boc or Alloc) and carboxylate functions (orthogonally protected as tBu or allyl ester)...
March 13, 2018: Journal of Organic Chemistry
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