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Quantum yield

Binbin Xie, Ganglong Cui, Wei-Hai Fang
In the present work, quantum trajectory mean-field (QTMF) approach is numerically implemented by ab initio calculation at the level of the complete active space self-consistent field, which is used to simulate photoisomerization of acetylacetone at ~265 nm. The simulated results shed light on the possible nonadiabatic pathways from the S2 state and mechanism of the photoisomerization. The in-plane proton transfer and the subsequent S2-S1 transition through the E-S2/S1-1 intersection region are the predominant route to the S1 state...
April 24, 2017: Journal of Chemical Theory and Computation
Angelo Giussani, Graham A Worth
Nitrobenzene is the simplest nitroaromatic compound and yet is characterized by a challenging and rich photophysics and photochemistry. In the present contribution the main decay paths undertaken by the system after UV absorption from both the brightest 1(La*) and the lowest 1(nA*) singlet excited states have been characterized by means of CASPT2//CASSCF computations. The obtained results match with the main photophysical properties experimentally reported: the lack of fluorescence and phosphorescence emission is justified by the presence of accessible conical intersections and intersystem crossing regions between respectively the 1(nA*) and 3(nA*) states with the ground state, while the high triplet quantum yield is attributable to the strong coupling between the 1(nA*) and 3(O*) states along the main decay path of the former...
April 24, 2017: Journal of Chemical Theory and Computation
Claudia Kleinlein, Shao-Liang Zheng, Theodore A Betley
Three ferric dipyrromethene complexes featuring different ancillary ligands were synthesized by one electron oxidation of ferrous precursors. Four-coordinate iron complexes of the type ((Ar)L)FeX2 [(Ar)L = 1,9-(2,4,6-Ph3C6H2)2-5-mesityldipyrromethene] with X = Cl or (t)BuO were prepared and found to be high-spin (S = (5)/2), as determined by superconducting quantum interference device magnetometry, electron paramagnetic resonance, and (57)Fe Mössbauer spectroscopy. The ancillary ligand substitution was found to affect both ground state and excited properties of the ferric complexes examined...
April 24, 2017: Inorganic Chemistry
Benoit Roubinet, Michael Weber, Heydar Shojaei, Mark Bates, Mariano L Bossi, Vladimir N Belov, Masahiro Irie, Stefan W Hell
A modular assembly of water soluble diarylethenes (DAEs), applicable as bio-markers for optical nanoscopy, is reported. Reversibly photoswitchable 1,2-bis(2-alkyl-6-phenyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentenes possessing a fluorescent "closed" form were decorated with one or two methoxy group(s) attached to the para-position(s) of phenyl ring(s) and two, four or eight carboxylic acid groups. Antibody conjugates of these DAEs feature low aggregation, efficient photoswitching in aqueous buffers, specific staining of cellular structures and photophysical properties (high emission efficiencies and low cycloreversion quantum yields) enabling their application in superresolution microscopy...
April 24, 2017: Journal of the American Chemical Society
Bess Vlaisavljevich, Johanna M Huck, Zeric Hulvey, Kyuho Lee, Jarad A Mason, Jeffrey B Neaton, Jeffrey R Long, Craig M Brown, Dario Alfè, Angelos Michaelides, Berend Smit
Small molecule binding in metal-organic frameworks (MOFs) can be accurately studied both experimentally and computationally, provided the proper tools are employed. Herein, we compare and contrast properties associated with guest binding by means of density functional theory (DFT) calculations using nine different functionals for the M2(dobdc) (dobdc4- = 2,5-dioxido,1,4-benzenedicarboxylate) series where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn. Additionally, we perform Quantum Monte Carlo (QMC) calculations for one system to determine if this method can be used to assess the performance of DFT...
April 24, 2017: Journal of Physical Chemistry. A
Ek Raj Thapaliya, Jaume Garcia-Amorós, Santi Nonell, Burjor Captain, Françisco M Raymo
Fluorescent 3H-indolium cations are valuable components for the realization of activatable fluorophores for bioimaging applications. Their relatively poor fluorescent quantum yields in organic solvents, however, appear to be in contradiction to their good performance in analytical methods based on single-molecule detection. The elucidation of the structural factors governing the excitation dynamics of these compounds is, therefore, essential to rationalize these effects and possibly guide the future design of activatable probes with improved performance...
April 24, 2017: Physical Chemistry Chemical Physics: PCCP
Qingqing Dou, Lu Jiang, Dan Kai, Cally Owh, Xian Jun Loh
Upconversion of light has attracted intensive studies for biomedical research, because it enables deeper [SB1] tissue analysis owing to the longer wavelength of incident light, compared with conventional downconversion fluorescent materials. Triplet-triplet annihilation (TTA), as a typical mechanism of upconversion, does not necessitate high power excitation and exhibits a higher quantum yield than rare earth upconversion owing to more sensitizer options with higher absorption coefficients. A desirable wavelength range of excitation and emission can be realized by careful selection of the combination of sensitizer and activator...
April 19, 2017: Drug Discovery Today
Derya Topkaya, Serap Alp
Coumarin-oxazol-5-one (COX), 3a-d, were synthesized with 7-methoxy-2-oxo-2H-chromene-4-carbaldehyde and benzoylglycine derivatives. The characterizations of the COX derivatives by (1)H NMR, FT-IR and elemental analysis were achieved. To obtain the photophysical data of the synthesized COX derivatives were used spectrophotometric and spectrofluorimetric methods. Evaluation of the absorption and emission properties of the structures was carried out in six different solvents. Maximum absorption and emission wavelengths (λ; nm), molar extinction coefficients (ε; cm(-1) M(-1)), Stoke's shifts (ΔλST; nm) and quantum yields (ϕF), of the COX derivatives were declared...
April 22, 2017: Journal of Fluorescence
Bogumil Zelent, Chris Bialas, Ignacy Gryczynski, Pan Chen, Rahul Chib, Karina Lewerissa, Maria G Corradini, Richard D Ludescher, Jane M Vanderkooi, Franz M Matschinsky
Five variants of glucokinase (ATP-D-hexose-6-phosphotransferase, EC including wild type and single Trp mutants with the Trp residue at positions 65, 99, 167 and 257 were prepared. The fluorescence of Trp in all locations studied showed intensity changes when glucose bound, indicating that conformational change occurs globally over the entire protein. While the fluorescence quantum yield changes upon glucose binding, the enzyme's absorption spectra, emission spectra and fluorescence lifetimes change very little...
April 22, 2017: Journal of Fluorescence
Wei Huang, Ying-Jie Yang, Jiao-Lin Zhang, Hong Hu, Shi-Bao Zhang
Our previous studies indicated that high light induced significant photoinhibition of photosystem I (PSI) in the shade-establishing tree species Psychotria henryi. However, the underlying mechanism has not been fully clarified. In the present study, in order to investigate the mechanism of PSI photoinhibition in P. henryi, we treated detached leaves with constant high light in the presence of methyl viologen (MV) or a soluble α-tocopherol analog, 2,2,5,7,8-pentamethyl-6-chromanol (PMC). We found that MV significantly depressed photochemical quantum yields in PSI and PSII when compared to PMC...
April 21, 2017: Photosynthesis Research
Adam Levi, Ehud Eilon, Amos Ori, Maarten van de Meent
We provide the first calculation of the renormalized stress-energy tensor (RSET) of a quantum field in Kerr spacetime (describing a stationary spinning black hole). More specifically, we employ a recently developed mode-sum regularization method to compute the RSET of a minimally coupled massless scalar field in the Unruh vacuum state, the quantum state corresponding to an evaporating black hole. The computation is done here for the case a=0.7M, using two different variants of the method: t splitting and φ splitting, yielding good agreement between the two (in the domain where both are applicable)...
April 7, 2017: Physical Review Letters
Yuezhi Mao, Yihan Shao, Jacek Dziedzic, Chris-Kriton Skylaris, Teresa Head-Gordon, Martin Head-Gordon
The importance of incorporating solvent polarization effects into the modeling of solvation processes has been well-recognized, and therefore a new generation of hybrid quantum mechanics/molecular mechanics (QM/MM) approaches that accounts for this effect is desirable. We present a fully self-consistent, mutually polarizable QM/MM scheme using the AMOEBA force field, in which the total energy of the system is variationally minimized with respect to both the QM electronic density and the MM induced dipoles. This QM/AMOEBA model is implemented through the Q-Chem/LibEFP code interface and then applied to the evaluation of solute-solvent interaction energies for various systems ranging from the water dimer to neutral and ionic solutes (NH3, NH4(+) , CN(-)) surrounded by increasing numbers of water molecules (up to 100)...
April 21, 2017: Journal of Chemical Theory and Computation
Bahram Ghanbari, Morteza Zarepour-Jevinani
The noticeable enhancement in fluorescence emission of O2N2-donor naphthodiaza-crown macrocyclic ligand (L) in the presence of Hg(2+) was observed in which the fluorescence quantum yield of free ligand L as well as L/Hg(2+) complex were found to be as 0.29 and 0.49, respectively. The observed ultra-low limit of detection (LOD) for Hg(2+) by L was determined as low as 1.0 × 10(-11) M in water. A 1:1 stoichiometry was also established for L/Hg(2+) together with a binding constant K BH = 66,543 by employing fluorescence spectrophotometry...
April 20, 2017: Journal of Fluorescence
Hanyang Gao, Chen Xue, Guoxin Hu, Kunxu Zhu
In this research, three kinds of graphene quantum dots (GQDs)-pristine graphene quantum dots (PGQDs), expanded graphene quantum dots (EGQDs) and graphene oxide quantum dots (GOQDs)-were produced from natural graphite, expanded graphite, and oxide graphite respectively in an ultrasound-assisted supercritical CO2 (scCO2)/H2O system. The effects of aqueous solution content ratio, system pressure, and ultrasonic power on the yields of different kinds of GQDs were investigated. According to these experiment results, the combination of the intense knocking force generated from high-pressure acoustic cavitation in a scCO2/H2O system and the superior penetration ability of scCO2 was considered to be the key to the successful exfoliation of such tiny pieces from bulk graphite...
July 2017: Ultrasonics Sonochemistry
Lena Grimmelsmann, Alireza Marefat Khah, Christian Spies, Christof Hättig, Patrick Nuernberger
Many synthetic DNA minor groove binders exhibit a strong increase in fluorescence when bound to DNA. The pharmaceutical-relevant berenil (diminazene aceturate) is an exception with an extremely low fluorescence quantum yield (on the order of 10(-4)). We investigate the ultrafast excited-state dynamics of this triazene by femtosecond time-resolved fluorescence experiments in water, ethylene glycol, and buffer and bound to the enzyme β-trypsin, the minor groove of AT-rich DNA, and G-quadruplex DNA. Ab initio calculations provide additional mechanistic insight...
April 20, 2017: Journal of Physical Chemistry Letters
Kun-You Chung, Yi-Han Chen, Yi-Ting Chen, Yen-Hao Hsu, Jiun-Yi Shen, Chi-Lin Chen, Yi-An Chen, Pi-Tai Chou
3-Me-2,6-diazaindole ((2,6-aza)Ind) was strategically designed and synthesized to probe water molecule catalyzed excited-state proton transfer in aqueous solution. Upon electronic excitation (λmax ~ 300 nm), (2,6-aza)Ind undergoes N(1)-H to N(6) long-distance proton transfer in neutral H2O, resulting in normal (340 nm) and proton-transfer tautomer (480 nm) emissions with an overall quantum yield of 0.25. The rate of the water-catalyzed proton transfer shows a prominent H/D kinetic isotope effect, which is determined to be 8...
April 20, 2017: Journal of the American Chemical Society
Donghyeop Shin, Tong Zhu, Xuan Huang, Oki Gunawan, Volker Blum, David B Mitzi
In recent years, Cu2 ZnSn(S,Se)4 (CZTSSe) materials have enabled important progress in associated thin-film photovoltaic (PV) technology, while avoiding scarce and/or toxic metals; however, cationic disorder and associated band tailing fundamentally limit device performance. Cu2 BaSnS4 (CBTS) has recently been proposed as a prospective alternative large bandgap (~2 eV), environmentally friendly PV material, with ~2% power conversion efficiency (PCE) already demonstrated in corresponding devices. In this study, a two-step process (i...
April 20, 2017: Advanced Materials
Kenji Kanazawa, Yuta Komiya, Kazuki Nakamura, Norihisa Kobayashi
The electroresponsive switching of red photoluminescence based on the electrochemical coloration of cyan-magenta-green (CMG) viologen components was achieved by combining a luminescent Eu(3+) chelate and viologen derivatives, resulting in CMG coloration in a single cell. The cell coloration was controlled by an electrochromic (EC) reaction, which also modulated the photoluminescence of the Eu(3+) chelate with high contrast, by transferring energy from the excited state of the Eu(3+) ion to the colored states of EC molecules...
April 20, 2017: Physical Chemistry Chemical Physics: PCCP
Salah E El-Hendawy, Wael M Hassan, Nasser A Al-Suhaibani, Yahya Refay, Kamel A Abdella
Field-based trials are crucial for successfully achieving the goals of plant breeding programs aiming to screen and improve the salt tolerance of crop genotypes. In this study, simulated saline field growing conditions were designed using the subsurface water retention technique (SWRT) and three saline irrigation levels (control, 60, and 120 mM NaCl) to accurately appraise the suitability of a set of agro-physiological parameters including shoot biomass, grain yield, leaf water relations, gas exchange, chlorophyll fluorescence, and ion accumulation as screening criteria to establish the salt tolerance of the salt-tolerant (Sakha 93) and salt-sensitive (Sakha 61) wheat cultivars...
2017: Frontiers in Plant Science
Hiroki Tanimoto, Junta Mori, Shunichiro Ito, Yasuhiro Nishiyama, Tsumoru Morimoto, Kazuo Tanaka, Yoshiki Chujo, Kiyomi Kakiuchi
This report describes the synthesis and characterization of arene-inserted type extended (ArEx) germa[N]pericyclynes composed of germanium and 1,4-diethynylbenzene units. These novel cyclic germanium-π unit materials were synthesized with diethynylbenzene and germanium dichloride. X-ray crystallographic analysis revealed their structures and the planar conformation of ArEx germa[4]pericyclyne along with the regulated aromatic rings. UV-vis absorption spectra and fluorescence emission spectra showed considerably unique and highly improved characters compared to previous germapericyclynes...
April 19, 2017: Chemistry: a European Journal
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