共查询到20条相似文献,搜索用时 15 毫秒
1.
Y. J. Shiu J. M. Zhang M. Hayashi V. Gulbinas C. M. Yang S. H. Lin 《Journal of Chemical Sciences》2002,114(6):611-621
Transient dynamics of allophycocyanin trimers and monomers are observed by using the pump-probe, transient absorption technique.
The origin of spectral components of the transient absorption spectra is discussed in terms of both kinetics and spectroscopy.
We find that the energy gap between the ground and excited states of the unexcited subunit of allophycocyanin monomer decreases
via an interaction with another excited subunit. For allophycocyanin trimer, we find that the fast dynamics results from the
fast internal conversion and the first excited state is the only one electronic state which can trap the final population. 相似文献
2.
Abstract— Octa-aL-alkyloxy-substituted Zn-phthalocyanines are an interesting class of far red-absorbing photosensitizers. The chemical structure, the calculated steric conformation, the observed linear optical properties and an anomalous luminescence from a higher than S, excited state are reported. To study the optical properties of higher excited states and their occupation dynamics up to delay times of 15 ns we have carried out measurements of transient absorption spectra after 14 ps pulsed, resonant B-band and Q-band excitation. From these measurements the excited state singlet-singlet and triplet-triplet spectra as well as the intersystem crossing (ISC) quantum yields are obtained. The main result is an excitation wavelength-dependent ISC quantum yield that can be explained by an additional ISC channel between higher excited singlet and triplet states. The large rate of this channel is justified by the resonance between higher triplet states, observed in the triplet-triplet spectrum and the B, absorption band. Using kinetic model calculations, a lifetime of the higher excited singlet state of some picoseconds is predicted and the influence of a two-step absorption process on the population density of this higher excited singlet state is discussed. 相似文献
3.
It is possible to study directly the absorption time-profiles of short-lived excited singlet states by sampling the transient excitation spectra for fluorescence from upper states. This approach has many advantages over direct absorption measurements, since the effects of triplet state absorption can be suppressed and the population time-profiles of excited singlet states can be studied in detail. The first direct measurements are reported of singlet state absorption time profiles in a number of aromatic aza- and carbonyl compounds. 相似文献
4.
Lazarides T Kuhri S Charalambidis G Panda MK Guldi DM Coutsolelos AG 《Inorganic chemistry》2012,51(7):4193-4204
In this report we describe the synthesis of multichromophore arrays consisting of two Bodipy units axially bound to a Sn(IV) porphyrin center either via a phenolate (3) or via a carboxylate (6) functionality. Absorption spectra and electrochemical studies show that the Bodipy and porphyrin chromophores interact weakly in the ground state. However, steady-state emission and excitation spectra at room temperature reveal that fluorescence from both the Bodipy and the porphyrin of 3 are strongly quenched suggesting that, in the excited state, energy and/or electron transfer might occur. Indeed, as transient absorption experiments show, selective excitation of Bodipy in 3 results in a rapid decay (τ ≈ 2 ps) of the Bodipy-based singlet excited state and a concomitant rise of a charge-separated state evolving from the porphyrin-based singlet excited state. In contrast, room-temperature emission studies on 6 show strong quenching of the Bodipy-based fluorescence leading to sensitized emission from the porphyrin moiety due to a transduction of the singlet excited state energy from Bodipy to the porphyrin. Emission experiments at 77 K in frozen toluene reveal that the room-temperature electron transfer pathway observed in 3 is suppressed. Instead, Bodipy excitation in 3 and 6 results in population of the first singlet excited state of the porphyrin chromophore. Subsequently, intersystem crossing leads to the porphyrin-based triplet excited state. 相似文献
5.
6.
Pritchina EA Gritsan NP Burdzinski GT Platz MS 《The journal of physical chemistry. A》2007,111(42):10483-10489
The primary photophysical and photochemical processes in the photochemistry of 1-acetoxy-2-methoxyanthraquinone (1a) were studied using femtosecond transient absorption spectroscopy. Excitation of 1a at 270 nm results in the population of a set of highly excited singlet states. Internal conversion to the lowest singlet npi* excited state, followed by an intramolecular vibrational energy redistribution (IVR) process, proceeds with a time constant of 150 +/- 90 fs. The 1npi* excited state undergoes very fast intersystem crossing (ISC, 11 +/- 1 ps) to form the lowest triplet pipi* excited state which contains excess vibrational energy. The vibrational cooling occurs somewhat faster (4 +/- 1 ps) than ISC. The primary photochemical process, migration of acetoxy group, proceeds on the triplet potential energy surface with a time constant of 220 +/- 30 ps. The transient absorption spectra of the lowest singlet and triplet excited states of 1a, as well as the triplet excited state of the product, 9-acetoxy-2-methoxy-1,10-anthraquinone (2a), were detected. The assignments of the transient absorption spectra were supported by time-dependent DFT calculations of the UV-vis spectra of the proposed intermediates. All of the stationary points for acyl group migration on the triplet and ground state singlet potential energy surfaces were localized, and the influence of the acyl group substitution on the rate constants of the photochemical and thermal processes was analyzed. 相似文献
7.
The hole burning spectra of phenol/ammonia (1:3 and 1:4) clusters were measured by a newly developed four-color (UV-near-IR-UV-UV) hole burning spectroscopy, which is a kind of population labeling spectroscopy. From the hole burning spectra, it was found that single species is observed in an n = 3 cluster, while three isomers are observed simultaneously for n = 4. A possibility was suggested that the reaction efficiency of the hydrogen transfer from the electronically excited phenol/ammonia clusters, which was measured by a comparison with the action spectra of the corresponding cluster, depends on the initial vibronic levels. 相似文献
8.
The electronic and vibrational structure of beta-carotene's early excited states are examined using femtosecond time-resolved stimulated Raman spectroscopy. The vibrational spectrum of the short-lived ( approximately 160 fs) second excited singlet state (S(2),1B(u) (+))of beta-carotene is obtained. Broad, resonantly enhanced vibrational features are observed at approximately 1100, 1300, and 1650 cm(-1) that decay with a time constant corresponding to the electronic lifetime of S(2). The temporal evolution of the vibrational spectra are consistent with significant population of only two low-lying excited electronic states (1B(u) (+) and 2A(g) (-)) in the ultrafast relaxation pathway of beta-carotene. 相似文献
9.
测定了新合成的α位取代和β位取代的四-(4-吡啶氧基)酞菁锌配合物的UV-Vis吸收光谱、荧光光谱及激发单重态寿命、纳秒瞬态吸收光谱与激发三重态寿命.在此基础上,与相关配合物进行了比较,探讨了取代基及其取代位置对酞菁锌配合物的吸收光谱、激发单重态寿命及激发三重态寿命的影响. 相似文献
10.
Semi-Empirical Model to Retrieve Finite Temperature Terahertz Absorption Spectra using Morse Potential
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Terahertz (THz) absorption is a fingerprint property of materials, due to the underlying low-frequency vibration/phonon modes being strongly dependent on the chemical constitutions and microscopic structures. The low excitation energies (0.414-41.4 meV) are related to two intrinsic properties of THz vibrations: the potential energy surfaces (PESs) are shallow, and the vibrationally excited states are usually populated via thermal fluctuations. The shallow PESs make the vibrations usually anharmonic, leading to redshifted vibrational excited state absorption; combined with considerable vibrational excited states population, characteristic THz signals are usually redshifted and congested with varying degrees at different temperatures. Combining existing experimental THz spectra at low temperatures, first principles vibration analysis, and the Morse potential, we developed a semi-empirical model to evaluate the anharmonicity of the low-frequency modes. The model was benchmarked with purine molecular crystal to generate THz spectra at different temperatures, the results were consistent with experiments. The good agreement suggests this model would facilitate the application of THz spectroscopy in molecular crystal characterization. 相似文献
11.
Lecointre J Roberts GM Horke DA Verlet JR 《The journal of physical chemistry. A》2010,114(42):11216-11224
Time-resolved photoelectron imaging of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion is presented. Photoelectron angular distributions (PADs) are qualitatively analyzed in terms of the simple s-p model that is based on symmetry arguments. The internal conversion dynamics from the first excited state (1(2)B(3u)) to the ground state ((2)B(2g)) may be observed through temporal changes in the PADs of the spectrally overlapping photoelectron features arising from photodetachment of the ground state and the excited state. A formulism for extracting the population dynamics from the β(2) anisotropy parameter of overlapping spectroscopic features is presented. This is used to extract the lifetime of the first excited state, which is in good agreement with that observed in the time-resolved photoelectron spectra. 相似文献
12.
The x-ray absorption near-edge spectra (XANES) and fluorescence spectra of molecules in the ground state and optically excited states are computed using time-dependent density functional theory and time-dependent Hartree-Fock theory. The calculated XANES spectra of optically excited methanol, benzonitrile, hydrogen sulphide, and titanium tetrachloride and the fluorescence spectra of optically excited methanol can be used to simulate ultrafast optical pump/x-ray probe experiments. 相似文献
13.
E. A. Pritchina N. P. Gritsan G. T. Burdzinski M. S. Platz 《Journal of Structural Chemistry》2007,48(1):S55-S63
The primary physical and chemical processes in the photochemistry of 1-(trideuteromethyl)-2,3,4-trideutero (1) and 1-acetoxy-2-methoxy-(2) 9,10-anthraquinones were studied using femtosecond transient absorption spectroscopy and computational chemistry. Excitation of 1 and 2 at 270 nm results in the population of a set of highly excited singlet states which decay within the laser pulse by internal conversion and vibrational energy redistribution. The transient absorption spectra of the lowest singlet and triplet excited states of substituted anthraquinones 1 and 2 as well as the triplet excited and ground states of the products were detected. The assignments of the transient absorption spectra were performed on the basis of quantum chemical calculations of the electronic absorption spectra of the intermediates. Time-dependent density functional theory or CASSCF/CASPT2 procedure were used to calculate the spectroscopic properties of the intermediates. 相似文献
14.
We study the diabatic crossing of two electronic surfaces from the time-dependent point of view, looking at the time and frequency-resolved spontaneous emission spectra and to the total population of the excited state, which for a pump and-probe experiment with two δ-like pulses, is proportional to the total emission. The results of some computations on a model case are presented and discussed. 相似文献
15.
Infrared emission following the photolysis of SO(2) by a 193 nm laser pulse (20 ns duration) was recorded with 500 ns time and 10 cm(-1) spectral resolution. Spectral analyses of the time-resolved spectra revealed the vibrationally excited nascent SO population distribution as (v = 1)/(v = 2)/(v = 3)/(v = 4)/(v = 5) = 0.54 ± 0.04, 1.00 ± 0.03, 0.00 ± 0.03, 0.01 ± 0.03, and 0.10 ± 0.03. The nascent SO was found to be rotationally excited with an average rotational temperature around 1000 K for v = 1 and v = 2 levels and 300 K for the v = 5 level. The vibrationally excited SO likely originates from two distinct dissociation mechanisms; the v = 1 and 2 populations are generated through intersystem crossing between the C state and a repulsive state (2(3)A'), and the v = 5 population is generated through internal conversion from the C to the X state. Efficient V-V energy transfer from nascent vibrationally excited SO to SO(2)(ν(1)) is also observed. The appearance of the SO(2)(ν(1)) ν(1) = 2 emission, before that from the ν(1) = 1 population is consistent with the previous report that the Δν = -2 channel is more efficient than the Δν = -1 channel. 相似文献
16.
Picosecond time-resolved Stokes and anti-Stokes resonance Raman spectra of all-trans-beta-carotene are obtained and analyzed to reveal the dynamics of excited-state (S(1)) population and decay, as well as ground-state vibrational relaxation. Time-resolved Stokes spectra show that the ground state recovers with a 12.6 ps time constant, in agreement with the observed decay of the unique S(1) Stokes bands. The anti-Stokes spectra exhibit no peaks attributable to the S(1) (2A(g) (-)) state, indicating that vibrational relaxation in S(1) must be nearly complete within 2 ps. After photoexcitation there is a large increase in anti-Stokes scattering from ground-state modes that are vibrationally excited through internal conversion. The anti-Stokes data are fit to a kinetic scheme in which the C=C mode relaxes in 0.7 ps, the C-C mode relaxes in 5.4 ps and the C-CH(3) mode relaxes in 12.1 ps. These results are consistent with a model for S(1)-S(0) internal conversion in which the C=C mode is the primary acceptor, the C-C mode is a minor acceptor, and the C-CH(3) mode is excited via intramolecular vibrational energy redistribution. 相似文献
17.
The jet-cooled spectra of isoquinoline and an isoquinoline-methanol complex are reported. The lifetimes, dispered fluorescence and excitation spectra are all discussed in terms of excited state interactions. Methanol complexation is found to be a useful probe of excited state level structure and dynamics. 相似文献
18.
Photoelectron spectra of naphthacene polycrystals excited with NeII and HeII resonance radiation have been measured. The spectra are compared with that excited with HeI resonance radiation. It is found that the corresponding peak positions of these three spectra are in good agreement with each other, while the peak intensity depends on the energy of the incident photon. The origin of the peak width in the photoelectron spectrum is discussed. 相似文献
19.
20.
F. P. Gay 《Journal of Polymer Science.Polymer Physics》1973,11(11):2227-2235
The thermal emission characteristics of polypyromellitimides have been examined as a function of temperature by measurement of the power required to maintain steady-state temperatures in an evacuated system. The emissivity was derived and found to increase with increasing temperature up to a saturation limit of above 0.9 at temperatures above 475°K. The effect is explained as a thermal population of excited infrared transitions. Power emitted is dominated by the most intense bands which are common to absorption and emission spectra. 相似文献