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Quantum yield

H Zimmermann, S Patchkovskii, M Ivanov, U Eichmann
Excitation and ionization in strong laser fields lies at the heart of such diverse research directions as high-harmonic generation and spectroscopy, laser-induced diffraction imaging, emission of femtosecond electron bunches from nanotips, self-guiding, filamentation and mirrorless lasing during propagation of light in atmospheres. While extensive quantum mechanical and semiclassical calculations on strong-field ionization are well backed by sophisticated experiments, the existing scattered theoretical work aiming at a full quantitative understanding of strong-field excitation lacks experimental confirmation...
January 6, 2017: Physical Review Letters
Sandesh Pai, Michael Moos, Maximilian H Schreck, Christoph Lambert, Dirk G Kurth
The structure and properties of metallo-supramolecular polyelectrolytes (MEPEs) self-assembled from rigid 2,6-bis(2-pyridyl)pyrimidine and the metal ions Fe(II) and Co(II) are presented. While FeL1-MEPE (L1 = 1,4-bis[2,6-bis(2-pyridyl)pyrimidin-4-yl]benzene) is deep blue, FeL2- and CoL2-MEPE (L2 = 5,5'-bis[2,6-bis(2-pyridyl)pyrimidin-4-yl]-2,2'-bithiophene) are intense green and red in color, respectively. These novel MEPEs display a high extinction coefficient and solvatochromism. Ligand L2 shows a high absolute fluorescence quantum yield (Φf = 82%)...
January 20, 2017: Inorganic Chemistry
T F Abelha, T W Phillips, J H Bannock, A M Nightingale, C A Dreiss, E Kemal, L Urbano, J C deMello, M Green, L A Dailey
This study compares the performance of a microfluidic technique and a conventional bulk method to manufacture conjugated polymer nanoparticles (CPNs) embedded within a biodegradable poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG5K-PLGA55K) matrix. The influence of PEG5K-PLGA55K and conjugated polymers cyano-substituted poly(p-phenylene vinylene) (CN-PPV) and poly(9,9-dioctylfluorene-2,1,3-benzothiadiazole) (F8BT) on the physicochemical properties of the CPNs was also evaluated. Both techniques enabled CPN production with high end product yields (∼70-95%)...
January 20, 2017: Nanoscale
Dharmendar Kumar Sharma, Shuzo Hirata, Lukasz Bujak, Vasudevanpillai Biju, Tatsuya Kameyama, Marino Kishi, Tsukasa Torimoto, Martin Vacha
We study the effect of Zn on the photophysical properties of a family of group I-III-VI nanocrystals (NCs), namely in solid solutions of (AgIn)xZn2(1-x)S2 (ZAIS). We focus on the comparison of the photoluminescence (PL) properties of ZAIS NCs of comparable sizes and different amounts of Zn. This approach helps us to decouple the effects of size and varying chemical composition of the NCs which both influence the PL properties. We show that in the presence of Zn new radiative centers are generated which improve the NC quality in terms of PL quantum yield...
January 20, 2017: Physical Chemistry Chemical Physics: PCCP
Xiaojuan Pang, Xueyan Cui, Deping Hu, Chenwei Jiang, Di Zhao, Zhenggang Lan, Fu-Li Li
Photoisomerization dynamics of a light-driven molecular rotary motor, 9-(2-methyl-2,3-dihydro-1H-cyclopenta[a]naphthalen-1-ylidene)-9H-fluorene, is investigated with trajectory surface-hopping dynamics at the semi-empirical OM2/MRCI level. The rapid population decay of the S1 excited state for the M isomer is observed, with two different decay timescales (500 fs and 1.0 ps). By weighting the contributions of fast and slow decay trajectories, the averaged lifetime of the S1 excited state is about 710 fs. The calculated quantum yield of the M-to-P photoisomerization of this molecular rotary motor is about 59...
January 19, 2017: Journal of Physical Chemistry. A
Wenbo Hu, Tingchao He, Rongcui Jiang, Jun Yin, Lin Li, Xiaomei Lu, Hui Zhao, Lei Zhang, Ling Huang, Handong Sun, Wei Huang, Quli Fan
Herein, we experimentally and theoretically demonstrate an unprecedentedly enhanced two-photon absorption in a small organic molecule by a simple introduction of an inner salt-shaped structure. Moreover, such an inner salt-shaped small molecule also exhibits superior singlet oxygen quantum yield and fascinating structure-inherent mitochondrial-targeting ability for highly efficient two-photon photodynamic therapy via a mitochondrial apoptosis pathway.
January 19, 2017: Chemical Communications: Chem Comm
Guo-Feng Jiang, Uromi Manage Goodale, Yan-Yan Liu, Guang-You Hao, Kun-Fang Cao
Mangroves in hypersaline coastal habitats are under constant high xylem tension and face great risk of hydraulic dysfunction. To investigate the relationships between functional traits and salt management, we measured 20 hydraulic and photosynthetic traits in four salt-adapted (SA) and two non-SA (NSA) mangrove tree species in south China. The SA species included two salt secretors (SSs), Avicennia marina (Forsskål) Vierhapper and Aegiceras corniculatum (L.) Blanco and two salt excluders (SEs), Bruguiera gymnorrhiza (L...
January 18, 2017: Tree Physiology
Svetlana V Eliseeva, Valerii S Liasotkyi, Iurii P Golovach, Pavel G Doga, Valery P Antonovich, Stéphane Petoud, Svetlana B Meshkova
Recently, a strong interest has been directed towards near-infrared (NIR) emitting lanthanide(III) compounds as they do possess complementary advantages in respect to organic molecules and semi-conductor nanocrystals, especially in the fields of biological analysis and imaging. To benefit from their emission, a key requirement to fulfill is the sensitization of lanthanide(III) cations with an appropriate chromophore. This condition is especially challenging to address for the lanthanide(III) cations emitting in the NIR...
January 18, 2017: Methods and Applications in Fluorescence
Klaas A Zachariasse, Attila Demeter, Sergey I Druzhinin
With 4-fluoro-N,N-dimethylaniline (DMA4F) only a single fluorescence from a locally excited (LE) state is observed, irrespective of solvent polarity, temperature, and excitation wavelength. The relatively small excited state dipole moment μe = 7.3 D confirms the identification as LE. The single exponential fluorescence decays in the nonpolar n-hexane (2.04 ns) and in the strongly polar acetonitrile (5.73 ns) are a further support. Similar results are obtained with 4-chloro-N,N-dimethylaniline (DMA4Cl), having a chlorobenzene subgroup, a somewhat better electron acceptor than the fluorobenzene moiety in DMA4F...
January 18, 2017: Journal of Physical Chemistry. A
Irina Rörich, Oleksandr V Mikhnenko, Dominik W Gehrig, Paul W M Blom, Nicoleta Irina Craciun
Using time-resolved photoluminescence (TRPL) spectroscopy the exciton lifetime in a range of conjugated polymers is investigated. For poly(p-phenylene vinylene) (PPV)-based derivatives and a polyspirobifluorene copolymer (PSBF) we find that the exciton lifetime is correlated with the energetic disorder. Better ordered polymers exhibit a single exponential PL decay with exciton lifetimes of a few hundred picoseconds, whereas polymers with a larger degree of disorder show multi-exponential PL decays with exciton lifetimes in the nanosecond regime...
January 18, 2017: Journal of Physical Chemistry. B
Henry Auer, Robin Guehne, Marko Bertmer, Sebastian Weber, Patrick Wenderoth, Thomas Christian Hansen, Jürgen Haase, Holger Kohlmann
Zintl phases form hydrides either by incorporating hydride anions (interstitial hydrides) or by covalent bonding of H to the polyanion (polyanionic hydrides), which yields a variety of different compositions and bonding situations. Hydrides (deuterides) of SrGe, BaSi, and BaSn were prepared by hydrogenation (deuteration) of the CrB-type Zintl phases AeTt and characterized by laboratory X-ray, synchrotron, and neutron diffraction, NMR spectroscopy, and quantum-chemical calculations. SrGeD4/3-x and BaSnD4/3-x show condensed boatlike six-membered rings of Tt atoms, formed by joining three of the zigzag chains contained in the Zintl phase...
January 18, 2017: Inorganic Chemistry
Shufan Chen, Xueqian Chen, Lijuan Zhang, Juanjuan Gao, Qiang Ma
In this paper, a facilely prepared electrochemiluminescence (ECL) biosensor was developed for Escherichia coli (E. coli) O157:H7 quantitative detection based on polydopamine (PDA) surface imprinted polymer (SIP) and nitrogen-doped graphene quantum dots (N-GQDs). N-GQDs with a high quantum yield of 43.2% were synthesized. The uniform PDA SIP film for E. coli O157:H7 was established successfully with a facile route. The dopamine and E. coli O157:H7 were mixed and electropolymerized directly on the electrode. After removed E...
January 18, 2017: ACS Applied Materials & Interfaces
José Ignacio García-Plazaola, Beatriz Fernández-Marín, Juan Pedro Ferrio, Josu G Alday, Günter Hoch, Damien Landais, Alexandru Milcu, David T Tissue, Jordi Voltas, Arthur Gessler, Jacques Roy, Víctor Resco de Dios
There is increasing evidence that the circadian clock is a significant driver of photosynthesis that becomes apparent when environmental cues are experimentally held constant. We studied whether the composition of photosynthetic pigments is under circadian regulation, and whether pigment oscillations lead to rhythmic changes in photochemical efficiency. To address these questions, canopies of bean and cotton were maintained, after an entrainment phase, under constant (light or darkness) conditions for 30-48 h...
January 18, 2017: Plant, Cell & Environment
Wei Shao, Guanying Chen, Tymish Y Ohulchanskyy, Chunhui Yang, Hans Ågren, Paras N Prasad
Photon management enables the manipulation of the number of input photons by conversion of two or more light quanta into one (upconversion) or vice versa (quantum cutting). Simultaneous realization of both these processes in a single unit provides unique opportunities of efficient utilization of photons throughout a broad spectral range. Yet, concurrent realization of these two parallel optical processes in one single unit remains elusive, limiting its impact on many existing or possible future applications such as for panchromatic photovoltaics...
January 18, 2017: Nanoscale
Dainis Kaldre, Boris Maryasin, Daniel Kaiser, Oliver Gajsek, Leticia González, Nuno Maulide
A general, asymmetric redox arylation of ynamides and thioalkynes with chiral sulfoxides is reported. This is the first example of a general 1,4-chirality transfer from sulfur to a carbon stereocenter through a sulfonium [3,3]-sigmatropic rearrangement. This reaction delivers α-arylated thioesters and amides under mild conditions in an atom-economical manner. The products are formed in high yields with enantiomeric ratios up to 99.5:0.5. Quantum chemical calculations suggest a mechanism for the chirality transfer from sulfur to carbon and explain the experimentally observed correlation of the enantioselectivity with both the catalyst and the substrate...
January 18, 2017: Angewandte Chemie
Hua Wang, Chun Sun, Xingru Chen, Yu Zhang, Vicki L Colvin, Quinton Rice, Jaetae Seo, Shengyu Feng, Shengnian Wang, William W Yu
Carbon dots (CDs) usually emit a strong blue light and excitation wavelength dependent long wavelength lights. This significantly limits their applications because one has to use a series of different excitation light sources to get different colors and the long wavelength emissions are usually very weak. We found that one type of CDs synthesized from p-phenylenediamine could emit various long wavelength lights (green to red) independent of the excitation wavelength when dispersed in different solvents. The photoluminescence quantum yields of the same CDs were 10-35% in different solvents for different color emissions...
January 17, 2017: Nanoscale
Zhitao Shen, Haitao Ma, Chunfang Zhang, Mingkai Fu, Yanan Wu, Wensheng Bian, Jianwei Cao
Encouraged by recent advances in revealing significant effects of van der Waals wells on reaction dynamics, many people assume that van der Waals wells are inevitable in chemical reactions. Here we find that the weak long-range forces cause van der Waals saddles in the prototypical C((1)D)+D2 complex-forming reaction that have very different dynamical effects from van der Waals wells at low collision energies. Accurate quantum dynamics calculations on our highly accurate ab initio potential energy surfaces with van der Waals saddles yield cross-sections in close agreement with crossed-beam experiments, whereas the same calculations on an earlier surface with van der Waals wells produce much smaller cross-sections at low energies...
January 17, 2017: Nature Communications
Andrey G Lvov, Alexey M Kavun, Vadim V Kachala, Yulia V Nelyubina, Anatoly V Metelitsa, Valerii Z Shirinian
The effect of the size of the ethene bridge on the structural and spectral properties of photochromic diarylethenes, which remains a poorly understood phenomenon, was studied as applied to diarylethenes containing unsymmetrical (cyclohexenone and cyclopentenone) and symmetrical (cyclohexene and cyclopentene) ethene bridges. Thiophene, oxazole, and imidazole derivatives were used as aryl moieties. An increase in the size of the ethene bridge in the cycloalkenone series was found to be accompanied by a hypsochromic shift of the absorption maximum of the photoinduced form, whereas no difference was found for cycloalkenes...
January 17, 2017: Journal of Organic Chemistry
Wook Lee, Spiridoula Matsika
Cyclobutane pyrimidine dimers (CPDs) are the most commonly formed photochemical products when nucleic acids interact with UV radiation. In duplex DNA, the relative inflexible structure allows for only the cis, syn CPD isomer to be formed. G-quadruplex structures, however, have loops that are more flexible and allow for different orientations of the bases to interact. As a result, the highly unusual formation of an anti CPD has been observed in these structures. Due to the close proximity between two opposing loops containing the TTA sequence in two G-quadruplex structures (called "form-3" and "basket"), a high yield of anti CPD formation was expected in these structures...
January 16, 2017: Physical Chemistry Chemical Physics: PCCP
Michael Kühn, Sergei Lebedkin, Florian Weigend, Andreas Eichhöfer
The optical properties of four isostructural trinuclear chalcogenolato bridged metal complexes [Cu2Sn(SPh)6(PPh3)2], [Cu2Sn(SePh)6(PPh3)2], [Ag2Sn(SPh)6(PPh3)2] and [Cu2Ti(SPh)6(PPh3)2] have been investigated by absorption and photoluminescence spectroscopy and time-dependent density functional theory (TDDFT) calculations. All copper-tin compounds demonstrate near-infrared (NIR) phosphorescence at ∼900-1100 nm in the solid state at low temperature, which is nearly absent at ambient temperature. Stokes shifts of these emissions are found to be unusually large with values of about 1...
January 16, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
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