排序方式: 共有63条查询结果,搜索用时 171 毫秒
31.
Larsen J Brüggemann B Polívka T Sundström V Akesson E Sly J Crossley MJ 《The journal of physical chemistry. A》2005,109(47):10654-10662
In this article, we explore energy transfer processes within a series of Zn-porphyrin-appended dendrimers by means of excitation intensity dependent transient absorption measurements. We report singlet-singlet annihilation on two distinct time scales of 18 +/- 5 ps and 130 +/- 10 ps in the dimer and the dendrimers. The two distinct processes reflect the presence of two structural conformer distributions. Analysis of the singlet-singlet annihilation transient kinetics shows that sequential annihilation occurs within subunits up to four Zn-porphyrins in the dendrimers. The onset of the singlet-singlet annihilation process depending on the size of the molecule reveals a difference in the number of communicating Zn-porphyrins. We further report a full characterization of the transient absorption kinetics of the monomer over a spectral range from 450 to 730 nm. 相似文献
32.
Žídek K Zheng K Ponseca CS Messing ME Wallenberg LR Chábera P Abdellah M Sundström V Pullerits T 《Journal of the American Chemical Society》2012,134(29):12110-12117
Photoinduced electron injection dynamics from CdSe quantum dots to ZnO nanowires is studied by transient absorption and time-resolved terahertz spectroscopy measurements. Ultrafast electron transfer from the CdSe quantum dots to ZnO is proven to be efficient already on a picoseconds time scale (τ = 3-12 ps). The measured kinetics was found to have a two-component character, whose origin is discussed in detail. The obtained results suggest that electrons are injected into ZnO via an intermediate charge transfer state. 相似文献
33.
Hideyuki Tatsuno Kasper S. Kjær Kristjan Kunnus Tobias C. B. Harlang Cornelia Timm Meiyuan Guo Pavel Chàbera Lisa A. Fredin Robert W. Hartsock Marco E. Reinhard Sergey Koroidov Lin Li Amy A. Cordones Olga Gordivska Om Prakash Yizhu Liu Mads G. Laursen Elisa Biasin Frederik B. Hansen Peter Vester Morten Christensen Kristoffer Haldrup Zoltán Németh Dorottya Sárosiné Szemes Éva Bajnóczi György Vankó Tim B. Van Driel Roberto Alonso-Mori James M. Glownia Silke Nelson Marcin Sikorski Henrik T. Lemke Dimosthenis Sokaras Sophie E. Canton Asmus O. Dohn Klaus B. Møller Martin M. Nielsen Kelly J. Gaffney Kenneth Wärnmark Villy Sundström Petter Persson Jens Uhlig 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(1):372-380
Iron N-heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub-ps X-ray spectroscopy study of an FeIINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot 3MLCT state, from the initially excited 1MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the 3MC state, in competition with vibrational relaxation and cooling to the relaxed 3MLCT state. The relaxed 3MLCT state then decays much more slowly (7.6 ps) to the 3MC state. The 3MC state is rapidly (2.2 ps) deactivated to the ground state. The 5MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the 3MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition-metal complexes for similar ultrafast decays to optimize photochemical performance. 相似文献
34.
So far it is not known whether epidermal melanins are solely photoprotective or also phototoxic. Also largely unknown are underlying UV-induced mechanisms and impact of the chemical structure. This perspective will focus on the current insights into the UV-dissipative mechanisms in melanin model systems and the implications for the in vivo pigments. We will also identify future research perspectives towards a full understanding of the functionality of epidermal pigments. 相似文献
35.
Amy Boylan Thien S. Nguyen Brian J. Lundy Jian-Yuan Li Ravikrishna Vallakati Sasha Sundstrom Jeremy A. May 《Molecules (Basel, Switzerland)》2021,26(6)
Two key factors bear on reaction rates for the conjugate addition of alkenyl boronic acids to heteroaryl-appended enones: the proximity of inductively electron-withdrawing heteroatoms to the site of bond formation and the resonance contribution of available heteroatom lone pairs to stabilize the developing positive charge at the enone β-position. For the former, the closer the heteroatom is to the enone β-carbon, the faster the reaction. For the latter, greater resonance stabilization of the benzylic cationic charge accelerates the reaction. Thus, reaction rates are increased by the closer proximity of inductive electron-withdrawing elements, but if resonance effects are involved, then increased rates are observed with electron-donating ability. Evidence for these trends in isomeric substrates is presented, and the application of these insights has allowed for reaction conditions that provide improved reactivity with previously problematic substrates. 相似文献
36.
Stefanie Tschierlei Martin Presselt Christian Kuhnt Arkady Yartsev Dr. Torbjörn Pascher Dr. Villy Sundström Prof. Dr. Michael Karnahl Matthias Schwalbe Dr. Bernhard Schäfer Dr. Sven Rau Prof. Dr. Michael Schmitt Dr. Benjamin Dietzek Dr. Jürgen Popp Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(31):7678-7688
Photoinduced electron‐transfer processes within a precatalyst for intramolecular hydrogen evolution [(tbbpy)2Ru(tpphz)PdCl2]2+ ( RuPd ; tbbpy=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine, tpphz=tetrapyrido[3,2‐a:2′,3′c:3′′,2′′,‐h:2′′′,3′′′‐j]phenazine) have been studied by resonance Raman and ultrafast time‐resolved absorption spectroscopy. By comparing the photophysics of the [(tbbpy)2Ru(tpphz)]2+ subunit Ru with that of the supramolecular catalyst RuPd , the individual electron‐transfer steps are assigned to kinetic components, and their dependence on solvent is discussed. The resonance Raman data reveal that the initial excitation of the molecular ensemble is spread over the terminal tbbpy and the tpphz ligands. The subsequent excited‐state relaxation of both Ru and RuPd on the picosecond timescale involves formation of the phenazine‐centered intraligand charge‐transfer state, which in RuPd precedes formation of the Pd‐reduced state. The photoreaction in the heterodinuclear supramolecular complex is completed on a subnanosecond timescale. Taken together, the data indicate that mechanistic investigations must focus on potential rate‐determining steps other than electron transfer between the photoactive center and the Pd unit. Furthermore, structural variations should be directed towards increasing the directionality of electron transfer and the stability of the charge‐separated states. 相似文献
37.
De S Pascher T Maiti M Jespersen KG Kesti T Zhang F Inganäs O Yartsev A Sundström V 《Journal of the American Chemical Society》2007,129(27):8466-8472
By measuring excited state and charge dynamics in blends of an alternating polyfluorene copolymer and fullerene derivative over nine orders in time and two orders in light intensity, we have monitored the light-induced processes from ultrafast charge photogeneration to much slower decay of charges by recombination. We find that at low light intensities relevant to solar cell operation relatively fast (approximately 30 ns) geminate recombination is the dominating charge decay process, while nongeminate recombination has a negligible contribution. The conclusion of our work is that under solar illumination conditions geminate recombination of charges may be directly competing with efficient charge collection in polymer/fullerene solar cells. 相似文献
38.
Scheblykin IG Yartsev A Pullerits T Gulbinas V Sundström V 《The journal of physical chemistry. B》2007,111(23):6303-6321
Conjugated polymers are becoming interesting materials for a range of optoelectronic applications. However, their often complex electronic and structural properties prevent establishment of straightforward property-function relationships. In this paper, we summarize recent results on the photophysics and excited state dynamics of conjugated polymers, in order to paint a picture of exciton formation, quenching, and generation of charge carriers. 相似文献
39.
Polívka T Niedzwiedzki D Fuciman M Sundström V Frank HA 《The journal of physical chemistry. B》2007,111(25):7422-7431
The role of the B800 in energy and electron transfer in LH2 complexes has been studied using femtosecond time-resolved transient absorption spectroscopy. The B800 site was perturbed by application of lithium dodecyl sulfate (LDS), and comparison of treated and untreated LH2 complexes from Rhodobacter sphaeroides incorporating carotenoids neurosporene, spheroidene, and spheroidenone was used to explore the role of B800 in carotenoid to bacteriochlorophyll-a (BChla) energy transfer and carotenoid radical formation. Efficiencies of the S1-mediated energy transfer in the LDS-treated complexes were 86, 61, and 57% in the LH2 complexes containing neurosporene, spheroidene, and spheroidenone, respectively. Analysis of the carotenoid S1 lifetimes in solution, LDS-treated, and untreated LH2 complexes allowed determination of B800/B850 branching ratio in the S1-mediated energy transfer. It is shown that B800 is a major acceptor, as approximately 60% of the energy from the carotenoid S1 state is accepted by B800. This value is nearly independent of conjugation length of the carotenoid. In addition to its role in energy transfer, the B800 BChla is the only electron acceptor in the event of charge separation between carotenoid and BChla in LH2 complexes, which is demonstrated by prevention of carotenoid radical formation in the LDS-treated LH2 complexes. In the untreated complexes containing neurosporene and spheroidene, the carotenoid radical is formed with a time constant of 300-400 fs. Application of different excitation wavelengths and intensity dependence of the carotenoid radical formation showed that the carotenoid radical can be formed only after excitation of the S2 state of carotenoid, although the S2 state itself is not a precursor of the charge-separated state. Instead, either a hot S1 state or a charge-transfer state lying between S2 and S1 states of the carotenoid are discussed as potential precursors of the charge-separated state. 相似文献
40.
Frontispiece: Palladium versus Platinum: The Metal in the Catalytic Center of a Molecular Photocatalyst Determines the Mechanism of the Hydrogen Production with Visible Light
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