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1.
The homogeneous optical linewidth of a spin-forbidden So → T1 transition in a chemically mixed organic crystal was directly measured in a two-pulse photon-echo experiment. The experimental values of T2Opt for the system dibromobenzophenone in dibromodiphenyl ether ranged from 1.4(3) to 3.8(2) μs, depending on the nuclear spins of the host. A temperature-dependent contribution to (T2Opt)?1 revealed an activation energy ΔE of 13.8(5) cm?1, which is tentatively attributed to a librational mode frequency. 相似文献
2.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1994,50(10):1783-1788
The experimental and theoretical results obtained for 5-methoxyindole (5MOI) indicate a large energetic difference between the S0 → S1 and S0 → S2 transitions indicating a charge distribution very different from that of indole. A weak shoulder on the long wavelength side of the S0 → S1 band is attributed to a nπ* transition associated with the methoxy substituent. This feature has previously been attributed to a hot band. The effect of solvent on the molecule and the results obtained by the quantitative quantum CNDO/2 and CNDO/M methods are discussed. 相似文献
3.
The two components of the dual phosphorescence of 1-indanone ( 1 ) and six related ketones ( 2–7 ) possess different excitation spectra exhibiting the vibrational progression characteristic of the S0 → S1 (n, π*) transition (shorter-lived emission) and two bands of the S0 → S2 and 3 (π,π*) 0–0 transitions, respectively. The most favorable intersystem crossing routes are S1 (n, π*) → T (n, π*) and S2,3 (π*) → T (π, π*). Internal conversion to S1 competes more effectively with S (π, π*) → T (π, π*) intersystem crossing only from higher vibrational levels of the S2 and S3 states. 相似文献
4.
In the spectrum of the delayed fluorescence (DF) of pyrene, caused by triplet-triplet annihilation T1 + T1 → Sn + So (n = 1,2), a strong DF S1 → So and a very weak DF S2 → s0 are observed. The DF S1→ So is quenched selectively by compounds like N-diethylanine or triethylamine which do not quench T1 of pyrene. 相似文献
5.
We present the S1 → S0 fluorescence spectrum, between 740 and 940 nm, of azulene solutions (10?3 M in methanol) excited with a Q-switched ruby laser. The nitrogen-laser excited S2 → S1 fluorescence spectrum, between 700 and 930 nm, is also reported. The transient S1 → Sn spectrum between 500 and 650 nm was studied, using synchronous nitrogen laser and dye laser excitation. The S5 (1B1(3)) state of azulene was found to be located at 45500 cm?1 and the cross section σ25 of the transient absorption S2 → S5 is estimated to be 3 × 10?18 cm2/molecule. 相似文献
6.
Hyoung‐Ryun Park Seo‐Eun Im Jung‐Ja Seo Bong‐Gon Kim Jin Ah Yoon Ki‐Min Bark 《Photochemistry and photobiology》2015,91(2):280-290
The specific fluorescence properties of morin (3,2′,4′,5,7‐pentahydroxyflavone) were studied in various CH3OH–H2O and CH3CN–H2O mixed solvents. Although the dihedral angle is large in the S0 state, morin has an almost planar molecular structure in the S1 state owing to the very low rotational energy barrier around the interring bond between B and the A, C ring. The excited state intramolecular proton transfer (ESIPT) at the S1 state cannot occur immediately after excitation, S1 → S0 fluorescence can be observed. Two conformers, Morin A and B have been known. At the CH3OH–H2O, Morin B will be the principal species but at the CH3CN–H2O, Morin A is the principal species. At the CH3OH–H2O, owing to the large Franck–Condon (FC) factor for S2 → S1 internal convernal (IC) and flexible molecular structure, only S1 → S0 fluorescence was exhibited. At the CH3CN–H2O, as the FC factor for S2 → S1 IC is small and molecular structure is rigid, S2 → S0 and S1 → S0 dual fluorescence was observed. This abnormal fluorescence property was further supported by the small pK1 value, effective delocalization of the lone pair electrons of C(2′)–OH to the A, C ring, and a theoretical calculation. 相似文献
7.
The ultrafast dynamics of benzaldehyde upon 260, 271, 284, and 287 nm excitations have been studied by femtosecond pinup-probe time-of-flight mass spectrometry. A bi-exponential decay component model was applied to fit the transient profiles of benzaldehyde ions and fragment ions. At the S2 origin, the first decay of the component was attributed to the internal conversion to the high vibrational levels of S1 state. Lifetimes of the first component decreased with increasing vibrational energy, due to the influence of high density of the vibrational levels. The second decay was assigned to the vibrational relaxation of the S1 whose lifetime was about 600 fs. Upon 287 nm excitation, the first decay became ultra-short (-56 fs) which was taken for the intersystem cross from S1 to T2, while the second decay component was attributed to the vibrational relaxation. The pump-probe transient of fragment was also studied with the different probe intensity at 284 nm pump. 相似文献
8.
Optical emission from e-beam excited liquid argon doped with OCS consists of a prominent S2(B 3Σ?u → X 3Σ?g) band progression (v′ = 0 to v″ = 5–18 and v′ = 1 to v″ = 4–8), similar to the observation made in an argon matrix, but with a lesser red shift. The time decay of these bands exhibits a fast component (<0.5μs) and a long non-exponential one, extending to 1 ms, that appears to be due to recombination of S(3P) atoms: S(3P) + S(3P) → S2(B 3Σ?u). Spectral study of the slow component (r > 5 μs) shows a peak at 456 nm identified as the S(1S → 3P) transition. A possible mechanism for this behavior is discussed. 相似文献
9.
When α,β-unsaturated γ-dimethoxymethyl cyclohexenones are excited to the S2(π,π*) state, certain unimolecular reactions can be observed to compete with S2 → S1 internal conversion. These reactions do not occur from the S1(n,π*) or the lowest T(π,π* and n,π*) states. They comprise the radical elimination of the formylacetal substituent (cf. 8 , 9 → 32 + 33 ), γ → α formylacetal migration (cf. 6 → 27 , 8 → 30 , 9 → 34 , 12 → 37 ), and a cyclization process involving the transfer of a methoxyl hydrogen to the α carbon and ring closure at the β position (cf. 6 → 28 , 8 → 31 , 12 → 38 , 20 → 40 + 41 ). The quantum yield of the ring closure 20a → 40a + 41a is 0.016 at ≤ 0.05M concentration. It is independent of the excitation wavelength within the π→π* absorption band (238–254 nm), but Φ ( 40a + 41a ) decreases at higher concentrations. According to the experimental data the reactive species of these specifically π→π*-induced transformations is placed energetically higher than the S1(n,π*) state, and it is either identical with the thermally equilibrated S2(n,π*) state, or reached via this latter state. The linear dienone 14 undergoes a similar π→π*-induced cyclization (→ 42 ) whereas the benzohomologue 26 proved unreactive, and the dienone 22 at both n → π and π→π* excitation only gives rise to rearrangements generally characteristic of cross-conjugated cyclohexadienones. 相似文献
10.
Bernhard Nickel 《Chemical physics letters》1979,68(1):17-20
The lowest triplet state of azulene, T1(Az), can be populated efficiently by triplet energy transfer from the lowest triplet state of fluoranthene, T1(F1). In isopentane at temperatures 120 K ? T ? 193 K a delayed fluorescence S2(Az) → S0(Az) is found, caused by hetero-triplet—triplet annihilation T1(Az) + T1(Fl) → S2(Az) + S0(F1). 相似文献
11.
Bernhard Nickel 《Helvetica chimica acta》1978,61(1):198-222
Delayed fluorescence (DF.) spectra of 1,2-benzanthracene, fluoranthene, pyrene, and chrysene in methylcyclohexane were measured at ?80° up to the wavenumber corresponding to the energy of two triplets. With all four compounds a weak DF. Sn → S0 from the highest state Sn accessible by triplet-triplet annihilation (TTA) was found. Lifetimes of Sn calculated (a) from the ratio of the DF's Sn → S0 and S1 → S0 and (b) from the difference in line-width of the 0,0-transitions Sn,0 ← S0,0 and S1,0 ← S0,0 agree reasonably well. This indicates that population of the highest accessible excited singlet state is the dominating primary process in the excited singlet channel of TTA. There is no evidence for excimer formation being the first step in TTA. DF. spectra extend up to the energy of two triplets. With pyrene the intensity distribution in the hot-band region of the DF. S2 → S0 suggests that in TTA the same vibrational selection rules are valid as in one-photon absorption S2 ← S0 and that vibrational relaxation within the S2 manifold is slow compared with internal conversion S2 ? S1. The experimental technique is described in detail and experimental difficulties arising from impurities and photoproduct formation are discussed. 相似文献
12.
A stochastic model of triplet yields is considered where the singlet S1 is initially excited and subsequently feeds the triplet T1. Both S1 and T1 have Montroll—Shuler step ladder vibrational relaxation mechanisms and radiative and non-radiative decay rates that vary linearly with increasing vibrational energy. Assuming the S1 → T1 rates also have this linear variation, the kinetic model is exactly solved in terms of integrals of simple functions of hyperbolic functions. The predictions of the model are illustrated by application to naphthalene. The model parameters are chosen; wherever possible, from experimental data. The predictions are in gross qualitative agreement with available experiments on triplet yields, and they indicate more detailed future experiments to separate the S1 → T1 and S1 → S0 (ground singlet) decays (and their energy dependence) in aromatic hydrocarbons. 相似文献
13.
Ab initio multiconfigurational CASSCF/MP2 method with the 6‐31G* basis set has been employed in studying the photochemistry of bicyclo[4.1.0]hept‐2‐ene upon direct photolysis. Our calculations involve the ground state (S0) and excited states (S1, T1, and T2). The ground‐state reaction pathways corresponding to the formation of the six products derived from bicyclo[4.1.0]hept‐2‐ene via two important diradical intermediates (D1 and D2) were mapped. It was found that there are various crossing points (conical intersections and singlet–triplet crossings) in the regions near D1 and D2. These crossing points imply that direct photolysis can lead to two possible radiationless relaxation routes: (1) S1 → S0, (2) S1 → T2 → T1 → S0. Computation indicates that the second route is not a competitive path with the first route during direct photolysis. The first route is initiated by barrierless cyclopropane bond cleavage to form two singlet excited diradical intermediates, followed by efficient decay to the ground‐state surface via three S1/S0 conical intersections in the regions near the diradical intermediates. All six ground‐state products can be formed via the three conical intersections almost without barrier after the decays. The barriers separating the diradical minima on S1 from the S1/S0 conical intersections were found to be very small with respect to the vertical excitation energy, which can explain why the product distribution is independent of excitation wavelength. Triplet surfaces are not involved in the first route, which agrees with the fact that the product contribution was unchanged by the addition of naphthalene. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
14.
We report a spectroscopic study of consecutive two-photon absorption of azulene excited in the range 32800–42000 cm?1, which provides information concerning the cross sections for the S1 → S3 and the S1 → S4 transitions. 相似文献
15.
We report the high resolution emission (S1 → S0, T1 → S0) and laser single site singlet excitation (S1 ← S0) spectra for the various insertion sites of coronene in n-heptane cooled to 1.5 K. The observation of site splitting of doubly degenerate vibrations and weak electric dipole forbidden 0, 0 bands in the S1 → S0 and T1 → S0 spectra indicates that the ground state, the first excited singlet and lowest triplet states are all distorted. In these spectra, the intensity distribution of the various sites in the 0, 0 bands suggests that the distortion is different from site to site but similar in S0, S1 and T1. Identical ordering of the sites in S1 S0 and S1 S0 spectra as well as the observation of weak shifts in the vibrational frequencies in the two states implies the absence of strong pseudo Jahn-Teller forces in the first excited singlet state. We propose, further, that this is also true for the triplet state. This conclusion is supported by the similarity in zero-field splitting parameters of coronene and deuterated coronene. Taken together, these results indicate strongly that the distortion of coronene in n-heptane is primarily crystal field induced and is not greatly changed upon excitation of the molecule to its lowest excited states. 相似文献
16.
Visible‐Light Photocatalytic Hydrogen Production Activity of ZnIn2S4 Microspheres Using Carbon Quantum Dots and Platinum as Dual Co‐catalysts
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ZnIn2S4 microspheres (ZIS MSs) were for the first time decorated with carbon quantum dots (CQDs) and platinum nanoparticles (NPs) as dual co‐catalysts of for photocatalytic H2 production. The ZIS MSs co‐loaded with CQDs and Pt exhibited a high photocatalytic H2 production rate of 1032.2 μmol h?1 g?1 with an apparent quantum efficiency of 2.2 % (420 nm) in triethanolamine aqueous solution under visible‐light irradiation, which was much higher than the respective photocatalytic rates of pure ZIS, Pt loaded ZIS, and CQDs‐decorated ZIS. Such a great enhancement was attributed to the integrative effect of good crystallization, enhanced light absorption, high electrical conductivity of CQDs, and the vectorial electron transfer from ZIS to CQDs and Pt NPs (ZIS→CQDs→Pt). 相似文献
17.
The photoexcitation routes used to produce molecular crystal, triplet states are shown to have important optical and microwave spectral consequences. 2-benzoylpyridine crystals at 4.2 K have T1 → S0 phosphorescence spectra showing line width dependence on whether initial production of the T1 state is through direct T1 → S0 absorption, or through S1 ← S0 absorption followed by S1 → T1 intersystem crossing. Striking differences are seen in the optically detected zero-field resonance spectra. 相似文献
18.
The long wavelength component of the emission occurring during the electron transfer reaction of the electrogenerated radical ions of 9,10-diphenylanthracene (DPA) in acetonitrile and 1,2-dimethoxyethane solutions, previously attributed to T2 → T1 emission, was investigated. Several sources contributing to detection of emission at wavelengths beyond 620 nm are discussed and the major source is attributed to a stable product formed by a small amount of decomposition of DPA radical cation. 相似文献
19.
In this paper we present the results of an experimental study of intermolecular electronic energy transfer (EET) from the short-lived Second excited singlet state of rhodamine 6G (R6G) to the ground state of 2,5-bis [5′-tert-butyl-2-benzoxazolyl] thiophene (BBOT). The S2 state of the donor was excited by sequential, time-delayed, two-photon excitation (STDTPE) utilizing the second harmonic and the first harmonic of a mode-locked Nd3+: glass laser, while the EET process was interrogated by monitoring the enhancement of the S1 → S0 fluorescence of BBOT. The enhancement of the fluorescence intensity of BBOT was found to be linear in the energies of the two exciting pulses, and linear in the concentration of the energy acceptor (over the BBOT concentration range of (0.3–7) × 10?5 M), which is in accord with the predictions of the Forster—Dexter mechanism for resonant EET from an ultrashort-lived donor state at low acceptor concentrations. Quantitative measurements of the S2 → S0 fluorescence yield in R6G solution directly excited by STDTPE and of the S1 → S0 fluorescence of BBOT from R6G + BBOT solutions resulting from EET led to the values of YD(S2 → S0) = (2.1 ± 0.5) × 10?6 for the emission quantum yield of the S2 state of R6G and τrD(S2) ≈ 3 × 10?14 s for the lifetime of the metastable S2 state of this molecule. 相似文献
20.
K. Lochner H. Bassler L. Sebastian G. Weiser G. Wegner V. Enkelmann 《Chemical physics letters》1981,78(2):366-370
The photoconductivity of DCHD displays a maximum near 3.6 eV coinciding with the maximum of the So → S1 absorption of the carbazole group. It is attributed to a sensitization involving charge transfer from the excited chromophore to the chain. The rate constant for non-radiative decay of the carbazole singlet due to energy transfer to the chain is 1.6 × 1013 s?1, and for charge transfer ≈ 3 × 1011 s?1. 相似文献