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1.
《Chemical physics》2002,275(1-3):15-30
The fluorescence anisotropic decay is modeled for the B850 bacteriochlorophyll a complex of the purple bacterium Rhodopseudomonas acidophila. Structural information is combined with experimental data to derive a Hamilton operator which models the S0–S1 excitation energy transfer between the pigments as well as the energy dissipation into the protein environment. The time-resolved fluorescence signal is determined from the solutions of the equations of motion for the one–exciton density matrix. Nonsecular terms in the Redfield relaxation tensor are shown to have a dramatic influence on the calculated time scales for depolarization.  相似文献   

2.
《Chemical physics letters》1987,136(2):181-186
Using optical detection via delayed fluorescence we have observed the Ty*–Tx zero-field transition of the triplet exciton in pure naphthalene at 1.2 K. This finding is compared with the results of a numerical calculation for the resonance frequency and linewidth of this transition.  相似文献   

3.
Direct excitation of overtone vibrations in combination with near-infrared fluorescence detection provides collisional relaxation rate constants for HF(v = 3,4) by HF, CH4 and CD4. Observing fluorescence from a few rotational levels shows that the rotational manifold in HF(v = 4) equilibrates in about half the gas kinetic collision time.  相似文献   

4.
Using the linear dependence of the ratio of direct and indirect integrated rotational line fluorescence on the inverse. Ar pressure, we obtain more accurate rate constants for rotational relaxation. k = (91.3 ± 1.9) × 103 Pa?1 s?1 and for vibrational plus electronic relaxation: k = (21.0 ± 0.9) × 103 Pa?1 s?1 of cw-laser-excited BaO(A 1Σ, ν′ = 8, J′= 49) in collision with Ar. The experiments were performed on BaO produced in a gas-flow system using oxidants N2O, O2 and CO2 at variable argon pressures.  相似文献   

5.
Proton spin lattice relaxation times have been measured for a variety of single crystal orientations of the (φ3AsCH3)+(TCNQ)2? ion radical salt over the temperature range of approximately 90 to 370°K. It is shown that the relaxation rate is directly proportional to the triplet exciton density where the exciton production energy is significantly dependent on temperature. The data suggests that exciton—exciton exchange is an important aspect in the relaxation mechanism.  相似文献   

6.
A gradual increase in delayed fluorescence intensity is observed in crystalline 2-chloroanthracene and 9,10-diphenylanthracene in air under irradiation with light of constant intensity in the first triplet band. Detailed measurements in 2-chloroanthracene of delayed fluorescence intensity and triplet exciton lifetime show that the behavior is consistent with a triplet exciton-oxygen interaction which results in a depletion of the ground-state molecular oxygen concentration in the lattice and leads to a time dependence of the triplet exciton lifetime and of the effective S0 → T1 absorption coefficient of the material.  相似文献   

7.
The VR,T rate in COF2 was measured directly by the ultrasonic absorption technique. The laser-induced fluorescence method was used to study VV exchange between the strongly pumped ν2, ν1 manifold and other vibrational degrees of freedom. At a few Torr a transition of the μm fluorescence from a single exponential decay to a relaxation spectrum is observed. This relaxation spectrum was analyzed by determining the “differential decay rate” for successive small time intervals. The relaxation spectrum is not changed by a pressure increase from ≈ 4 to 15 Torr. Similarly, relatively large amounts of Xe must be added before a change in the relaxation behavior of COF2 can be detected. C2H6 is a very effective quencher of the 5μm fluorescence.  相似文献   

8.
Electronically controlled photon-echo relaxation measurements, using two nitrogen pumped dye-lasers, are reported for mixed crystals of pentacene-h14 and -d14 in p-terphenyl-h14 at 1.5 K. In dilute mixed crystals (ca. 10?8 M) the photon-echo lifetime is found to be exclusively determined by the fluorescence lifetime. Homogeneous linewidths of 7.1 and 5.9 MHz at 1.5 K are then calculated for the electronic origin of the 1B2u1A1g transition of pentacene-h14 and -d14 respectively. The decrease in photon-echo lifetime at higher guest concentrations (ca. 10?7 M) is ascribed to energy transfer between excited and neutral guest molecules.  相似文献   

9.
Rational manipulation of energy utilization from excited-state radiation of theranostic agents with a donor–acceptor structure is relatively unexplored. Herein, we present an effective strategy to tune the exciton dynamics of radiative excited state decay for augmenting two-photon nanotheranostics. As a proof of concept, two thermally activated delayed fluorescence (TADF) molecules with different electron-donating segments are engineered, which possess donor–acceptor structures and strong emissions in the deep-red region with aggregation-induced emission characteristics. Molecular simulations demonstrate that change of the electron-donating sections could effectively regulate the singlet–triplet energy gap and oscillator strength, which promises efficient energy flow. A two-photon laser with great permeability is used to excite TADF NPs to perform as theranostic agents with singlet oxygen generation and fluorescence imaging. These unique performances enable the proposed TADF emitters to exhibit tailored balances between two-photon singlet oxygen generation and fluorescence emission. This result demonstrates that TADF emitters can be rationally designed as superior candidates for nanotheranostic agents by the custom controlling exciton dynamics.

Exciton dynamics can be manipulated rationally in the design of TADF materials for nanotheranostics. Regulating the ΔEST and f promises efficient energy flow for tailoring balances between singlet oxygen generation and fluorescence emission.  相似文献   

10.
The donor-acceptor interface plays a critically important role in determining the power conversion efficiency of organic solar cells via controlling charge separation (CS) and recombination (CR) processes. Here, we combine the electronic structure calculations with electron transfer rate theory to clarify the CS and CR processes in ThQs-C60 /PDIxCN2 donor-acceptor complexes. The results reveal that in ThQs-PDIxCN2 the CS comes from both the dissociations of photo-induced singlet exciton and singlet fission-induced triplet exciton with a high efficiency, whereas in ThQs-C60 only the singlet exciton dissociation can take place because the triplet exciton lies below the charge-transfer exciton. However, very high CR rates in ThQs-PDIxCN2 obliterate the benefit of fast CS, inversely leading to the ThQ-C60 complex with a better cell efficiency. The present results are consistent with experimental observation and may furnish a possible patten to improve the overall conversion efficiency. © 2018 Wiley Periodicals, Inc.  相似文献   

11.
CW dye laser induced fluorescence emission and thermal emission spectra of YO-molecules in a 1 atm H2O2Ar flame of 2430 K were recorded simultaneously. Narrow band laser excitation was applied to four rotational lines in the (1, 1) Q-branch of the A2Π32X2Σ+ transition and broadband excitation was applied to several separate Q-branches of the A2Π12,32X2Σ+ transitions. From the differences between the fluorescence emission spectra and thermal emission spectra, we conclude that collisional de-excitation of an excited vibronic level takes place by vibrational relaxation, decay to the electronic ground state and by intermultiplet transfer in order of increasing probability.  相似文献   

12.
The 13C relaxation times (T1 and T2) and isotropic contact shifts (Δω) of a one molar aqueous solution of l-proline at pH = 11 (or pD = 11.4) containing ca 10?4 M copper(II) perchlorate are measured at 62.86 MHz over a temperature range of 26–70°C. The purely dipolar longitudinal relaxation of carbon-13 nuclei contrasting with purely scalar transverse relaxation allowed us to extract carbon-to-metal distances (through T1 measurements) and hyperfine coupling constants and dynamic parameters (from T2 and Δω measurements). The structure of the complex in solution is found closely similar to that in the solid state. Curve-fitting procedures allowed us to derive the hyperfine electron—carbon coupling constants Ac = ?1.95, + 0.42, + 1.90 and ?1.70 MHz for carbons α, β, γ, δ, of the pyrrolidinic ring, the reorientation correlation time of the complex, τR (25°C) = 1.15 × 10?10 sec, the l-proline exchange rate, kM (25°C) = 4.0 × 105 sec?1 (and the corresponding activation parameters ΔH = 9.0 kcal mol?1 and ΔS = ?0.7 e.u.), and the electronic relaxation time, T1e = 1.13 × 10?8 sec (at 25°C). The latter value was found in agreement with the one computed from ESR data and the above τR value, showing the predominant contributions of spin—rotation interaction and, to a lesser extent, of the effect of g-tensor anisotropy to the electronic relaxation rate.  相似文献   

13.
The electronic energy transfer process Hg(6 3P0) + OH(X2Πi, υ = 0,K) → Hg(6 1S0) + OH(A 2Σ+, υ,K) has been studied by the sensitized fluorescence method. A rather broad spectrum of rotational population, Nυ′K, was obtained under conditions of minimum relaxation, which illustrates the non-resonant and non-optical nature of this energy transfer process. The fractions of the exoergicity, above electronic excitation of OH(A 2Σ+, υ = 0, K = 0), going into vibrational, rotational and translational excitation are 0.11, 0.31, and 0.58, respectively. A statistical mode of energy partitioning, such as would result from long-lived complex formation, seems to account well for these observations.  相似文献   

14.
The analysis of the variation with incident flux of the time dependence of the delayed fluorescence in conjunction with the determination of the absolute ground state-first excited triplet absorption coefficients at room temperature, yields the value of γtot = (5.5 ± 2.0) × 10?12 cm3 s?1, for the total triplet-triplet annihilation rate constant in 1,4-dibromonaphthalene crystals. The one-dimensional mutual annihilation rate constant for the triplet exciton motion restricted to linear chains along the crystal c axis is γ1tot = (1.0 ± 0.4) × 103 cm s?1. The results are discussed in terms of recent theories of mutual annihilation of triplets in one-dimensional systems.  相似文献   

15.
《Chemical physics letters》1986,126(6):487-494
Some universal characteristics are discussed of the decay lifetimes and fluorescence quantum yields from the S1 manifold of large molecules, which originate from the coupling between intrastate vibrational energy redistribution and interstate electronic relaxation. The time-resolved total fluorescence decay from the S1 state of jet-cooled 9-cyanoanthracene exhibits non-exponential decay in the energy range Ev= 1200–1740 cm−1 above the S1 origin, which does not originate from dephasing but rather manifests the effects of intrastate intermediate level structure for vibrational energy redistribution on intersystem crossing.  相似文献   

16.
Previous ab initio LCAO Hartree-Fock (HF) self-consistent field (SCF) band structure calculations predicted the alternating all trans (CH)x (polyacetylene or polyene) to be energetically more stable than the equidistant metallic chain, however, the gap of those calculations was too large (≈7 eV). The present discussion based on semi-empirical PPP hamiltonian explains how electronic correlation neglected in the HF theory reduces this gap to ≈4 eV, while the excitation energy for the creation of excitons is estimated to be below 2 eV. The formalism for this estimation is an intermediate-binding exciton theory with explicit use of numerical Wannier functions. It is concluded that the gap is not due to a spin-density-wave state of the equidistant chain, as expected by Ovchinnikov .  相似文献   

17.
Subsequent to exciting v3 by a CO2 laser pulse, fluorescence has been detected from 2v3 of CH3F trapped in rare gas matrices. 2v3 is activated by V-V energy transfer and deactivates at twice the rate of v3 relaxation. A kinetic model is presented to interpret these observations.  相似文献   

18.
The vibrational relaxation time for CO2(v3) + O(3P) has been measured by laser fluorescence. The observed value, βCO2.O = 0.21 ± 0.04 μsec, is an order of magnitude lower than the relaxation time for self-collisions.  相似文献   

19.
20.
Picosecond delayed CARS experiments on totally symmetric modes in naphthalene at 1.5 K are reported. The Raman lineshape of the vibrational excitons is lorentzian and vibrational relaxation can be surprisingly slow. The Raman lineshape of the Ag exciton level of the 766 cm?1 vibrational mode reveals that the low-temperature lorentzian lineshape occurs by motional narrowing At higher temperature the exciton is trapped by interaction with lattice phonons.  相似文献   

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