共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
Wenger OS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(42):11692-11702
Proton-coupled electron transfer (PCET) is of fundamental importance for small-molecule activation processes, such as water splitting, CO(2)-reduction, or nitrogen fixation. Ideally, energy-rich molecules such as H(2), CH(3)OH, or NH(3) could be generated artificially using (solar) light as an energy input. In this context, PCETs originating directly from electronically excited states play a crucial role. A variety of transition-metal complexes have been used recently for fundamental investigations of this important class of reactions, and the key findings of these studies are reviewed in this article. The present minireview differs from other reviews on the subject of PCET in that it focuses specifically on reactions occurring directly from electronically excited states. 相似文献
7.
The ML(4) complexes formed by reaction between the bidentate azulene-based ligand diethyl 2-hydroxyazulene-1,3-dicarboxylate (HAz) and several lanthanide cations (Pr(3+), Nd(3+), Gd(3+), Ho(3+), Er(3+), Tm(3+), Yb(3+), and Lu(3+)) have been synthesized and characterized by elemental analysis, FT-IR vibrational spectroscopy and electrospray ionization mass spectroscopy. Spectrophotometric titrations have revealed that four Az(-) ligands react with one lanthanide cation to form the ML(4) complex in solution. Studies of the luminescence properties of these ML(4) complexes demonstrated that Az(-) is an efficient sensitizer for four different near-infrared emitting lanthanide cations (Nd(3+), Er(3+), Tm(3+), and Yb(3+)); the resulting complexes have high quantum yield values in CH(3)CN. The near-infrared emission arising from Tm(3+) is especially interesting for biologic imaging and bioanalytical applications since biological systems have minimal interaction with photons at this wavelength. Hydration numbers, representing the number of water molecules bound to the lanthanide cations, were obtained through luminescence lifetime measurements and indicated that no molecules of water/solvent are bound to the lanthanide cation in the ML(4) complex in solution. The four coordinated ligands protect well the central luminescent lanthanide cation against non-radiative deactivation from solvent molecules. 相似文献
8.
Cover Picture: Electron–Proton Decoupling in Excited‐State Hydrogen Atom Transfer in the Gas Phase (Angew. Chem. Int. Ed. 50/2015)
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mitsuhiko Miyazaki Ryuhei Ohara Kota Daigoku Kenro Hashimoto Jonathan R. Woodward Claude Dedonder Christophe Jouvet Masaaki Fujii 《Angewandte Chemie (International ed. in English)》2015,54(50):14981-14981
9.
Mark M. Maturi Matthias Wenninger Dr. Rafael Alonso Dr. Andreas Bauer Dr. Alexander Pöthig Prof. Dr. Eberhard Riedle Prof. Dr. Thorsten Bach 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7461-7472
The intramolecular [2+2] photocycloaddition of four 4‐(but‐3‐enyl)oxyquinolones (substitution pattern at the terminal alkene carbon atom: CH2, Z‐CHEt, E‐CHEt, CMe2) and two 3‐(but‐3‐enyl)oxyquinolones (substitution pattern: CH2, CMe2) was studied. Upon direct irradiation at λ=300 nm, the respective cyclobutane products were formed in high yields (83–95 %) and for symmetrically substituted substrates with complete diastereoselectivity. Substrates with a Z‐ or E‐substituted terminal double bond showed a stereoconvergent reaction course leading to mixtures of regio‐ and diastereomers with almost identical composition. The mechanistic course of the photocycloaddition was elucidated by transient absorption spectroscopy. A triplet intermediate was detected for the title compounds, which–in contrast to simple alkoxyquinolones such as 3‐butyloxyquinolone and 4‐methoxyquinolone–decayed rapidly (τ≈1 ns) through cyclization to a triplet 1,4‐diradical. The diradical can evolve through two reaction channels, one leading to the photoproduct and the other leading back to the starting material. When the photocycloaddition was performed in the presence of a chiral sensitizer (10 mol %) upon irradiation at λ=366 nm in trifluorotoluene as the solvent, moderate to high enantioselectivities were achieved. The two 3‐(but‐3‐enyl)oxyquinolones gave enantiomeric excesses (ees) of 60 and 64 % at ?25 °C, presumably because a significant racemic background reaction occurred. The 4‐substituted quinolones showed higher enantioselectivities (92–96 % ee at ?25 °C) and, for the terminally Z‐ and E‐substituted substrates, an improved regio‐ and diastereoselectivity. 相似文献
10.
11.
12.
Excited‐state relaxation of linear merocyanine dyes in solution is investigated using time‐resolved spectroscopy techniques and quantum chemical calculations. The merocyanine L‐Mero4 and phenyl‐substituted P‐L‐Mero4 have a S‐trans and S‐cis structure, respectively, consisting of indole moiety as the donor, indandione as the acceptor, and the tetramethine as the bridge. The time‐correlated single‐photon counting (TCSPC) picosecond measurements after excitation at wavelength 515 nm to the ππ* state yield emission curves with a short component τ1 in the range of 27–160 ps and a second component τ2 of 200–780 ps for L‐Mero4. In P‐L‐Mero4, τ1 lies in the range of 18–150 ps and τ2 220–520 ps. The subfemtosecond transient absorption measurements yield a short component around 0.4–1.4 ps, and the second/third components are similar to those in the TCPSC measurements. The analysis of the experimental data demonstrates that the ground state recovery exhibits a biexponential rise and rapidly indicates that the conversion back to the electronic ground state provides a fast, nonradiative pathway. Quantum chemical calculations on the electronic structures and their dependence on the molecular confirmation are performed. We identify the excited states and the relaxation path along the twist of the center double bonds in tetramethine that might be the nonradiative pathway. The C=C double bond is weakened in the ππ* state. The phenyl substitution in the conjugated double bond weakens this C=C bond, lowers the isomerization barrier, increases the nonradiative rate, and reduces the emission quantum yield. In polar solvents, the energy of the perpendicular conformer along the trans–cis isomerization path is increased to achieve less coupling to the ground state surface. Because of the small barrier to the trans form, these two conformers establish an equilibrium condition. The trans form, which lies at a lower energy, gains more population and thus has a higher emission yield. 相似文献
13.
Takada T Kawai K Fujitsuka M Majima T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(13):3835-3842
A kinetic study of the single-step hole transfer in DNA was performed by measuring time-resolved transient absorption. DNA molecules with various sequences were designed and conjugated with naphthalimide (NI) and phenothiazine (PTZ) to investigate the sequence and distance dependence of the single-step hole transfer between guanines (Gs). Hole injection into DNA was accomplished by excitation of the NI site with a 355 nm laser pulse, and the kinetics of the hole-transfer process were investigated by monitoring the transient absorption of the PTZ radical cation (PTZ.+). Kinetic analysis of the time profile of PTZ.+ based on the kinetic model showed that the distance dependence of the hole-transfer process was significantly influenced by the DNA sequence. Results of temperature- and isotope-effect experiments demonstrated that the activation energy increased as the number of bridge bases separating the Gs increased. This is because of the distance-dependent reorganization energy and contribution of the proton-transfer process to the hole transfer in DNA. 相似文献
14.
Houjou H Takezawa S Oyamada I Matsumura K Seino H Yoshikawa I Mizobe Y Araki K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(4):1122-1127
We have developed a novel triphenylmethane-based hexanuclear zinc complex that exhibits peculiar photochemical and photophysical properties. Upon UV irradiation, the compound turned from colorless to reddish purple, while the color of emission turned from blue to red. The color change was attributed to an oxidation of the ligand part. It was suggested that an intramolecular energy-transfer mechanism operates to give rise to the red emission. The UV treatment of a single crystal results in simultaneous emission of orthogonally polarized blue and red light. This color switching, namely linear dichroic emission was so distinct that one can recognize with by sight through optical microscope. The columnar arrangement of molecules in the crystal clearly accounts for the observed polarization of the emission. 相似文献
15.
16.
17.
Kenichi Ataka Dr. Tilman Kottke Dr. Joachim Heberle Prof. Dr. 《Angewandte Chemie (International ed. in English)》2010,49(32):5416-5424
New techniques in vibrational spectroscopy are promising for the study of biological samples as they provide exquisite spatial and/or temporal resolution with the benefit of minimal perturbation of the system during observation. In this Minireview we showcase the power of modern infrared techniques when applied to biological and biomimetic systems. Examples will be presented on how conformational changes in peptides can be traced with femtosecond resolution and nanometer sensitivity by 2D IR spectroscopy, and how surface‐enhanced infrared difference absorption spectroscopy can be used to monitor the effect of the membrane potential on a single proton‐transfer step in an integral membrane protein. Vibrational spectra of monolayers of molecules at basically any interface can be recorded with sum‐frequency generation, which is strictly surface‐sensitive. Chemical images are recorded by applying scanning near‐field infrared microscopy at lateral resolutions better than 50 nm. 相似文献
18.
19.
Dr. Tomokazu Umeyama Junya Mihara Noriyasu Tezuka Prof. Dr. Yoshihiro Matano Kati Stranius Dr. Vladimir Chukharev Prof. Dr. Nikolai V. Tkachenko Prof. Dr. Helge Lemmetyinen Dr. Kei Noda Prof. Dr. Kazumi Matsushige Prof. Dr. Tetsuya Shishido Dr. Zheng Liu Kaori Hirose‐Takai Prof. Dr. Kazu Suenaga Prof. Dr. Hiroshi Imahori 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(14):4250-4257
Chemically converted graphene (CCG) covalently linked with porphyrins has been prepared by a Suzuki coupling reaction between iodophenyl‐functionalized CCG and porphyrin boronic ester. The covalently linked CCG–porphyrin composite was designed to possess a short, rigid phenylene spacer between the porphyrin and the CCG. The composite material formed stable dispersions in DMF and the structure was characterized by spectroscopic, thermal, and microscopic measurements. In steady‐state photoluminescence spectra, the emission from the porphyrin linked to the CCG was quenched strongly relative to that of the porphyrin reference. Fluorescence lifetime and femtosecond transient absorption measurements of the porphyrin‐linked CCG revealed a short‐lived porphyrin singlet excited state (38 ps) without yielding the porphyrin radical cation, thereby substantiating the occurrence of energy transfer from the porphyrin excited state to the CCG and subsequent rapid decay of the CCG excited state to the ground state. Consistently, the photocurrent action spectrum of a photoelectrochemical device with a SnO2 electrode coated with the porphyrin‐linked CCG exhibited no photocurrent response from the porphyrin absorption. The results obtained here provide deep insight into the interaction between graphenes and π‐conjugated systems in the excited and ground states. 相似文献
20.