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1.
Fluorescence and excitation spectra of coronene vapor have been measured under different conditions. Weak emission which can be regarded as the fluorescence from the third excited singlet state, S 3( 1E 1u), was observed in addition to the S 1( 1B 2u) and S 2( 1B 1u) fluorescence. The observed S 2 and S 3 fluorescence are substantially different from those reported previously for coronene vapor. Addition of oxygen resulted in significant decrease of the S 1 fluorescence intensity, but did not affect the S 2 fluorescence intensity, indicating the faster decay rate of the S 2 state than that of S 1. Excitation energy dependence of the S 1, S 2 and S 3 fluorescence quantum yields (Φ F(S 1), Φ F(S 2) and Φ F(S 3), respectively) revealed that Φ F(S 1) decreases with increasing excitation energy, while Φ F(S 2) and Φ F(S 3) increase significantly. The quantum yield ratios, Φ F(S 2)/Φ F(S 1) and Φ F(S 3)/Φ F(S 2), obtained as a function of excitation energy are correlated with the ratios of the relative internal conversion rates. 相似文献
2.
In polar and nonpolar solvents, tetrahydroisoquinoline emits S 2 (ππ 1) → S 0 and S 1 (ππ 1) → S 0 dual fluorescence and T 1 (ππ 1) → S 0 phosphorescence on S 2 (ππ 1) ← S 0 excitation. When excited by S 1 (ππ 1) ← S 0 the molecule yields S 1 (ππ 1) → S 0 fluorescence and T 1 (ππ 1) → S 0 phosphorescence in nonpolar solvent but only fluorescence in polar solvents. Probable participation of intermediate S 1 (nπ 1), T 1(nπ 1) states in intersystem crossing and internal conversion processes and its significance in interpreting the results are discussed. 相似文献
3.
The excited trip-sextet ( 6T 1) state of chloro-(3-methylimidazol)-( meso-tetraphenylporphyrinato) chromium(III) (Cr IIIP) is quenched by 1,1′-dibenzyl-4,4′-bipyridinium (BV 2+) in acetonitrile through electron transfer to give 5(Cr IIIP ·+) and 2BV ·+. The intermediate is a geminate ion pair in the sextet (Sx) state 6[ 5(Cr IIIP ·+) 2BV ·+], which decays through either the escape from a solvent cage to give the free ions or the spin conversion to the quartet (Qa) state followed by back electron transfer. The free ion yield (Φ FI) increased with increasing magnetic field from 0 to 4 T and then slightly decreased from 4 T to 10 T. These magnetic field effects are explained as follows. Under low fields where the Zeeman splitting of the spin sublevels is lower than or comparable with the electron spin dipole—dipole interaction within 5(Cr IIIP ·+), this interaction effectively induces the Sx → Qa conversion of [ 5(Cr IIIP ·+) 2BV +] to result in low Φ FI values. Under high fields where the Zeeman splitting is larger than the dipole—dipole interaction, the Sx → Qa conversion is decreased with increasing field to cause higher Φ FI values. The slight decrease in Φ FI above 4 T may be due to the Δ g mechanism. 相似文献
4.
We investigate a simple example of a “transport-phase-transition” in a phonon system (linear chain) including a localized mode. For increasing (decreasing) energy flux there is a critical value Φ cu(Φ cl) for which the local excitation “jumps” from the “thermodynamic” to a nonthermodynamic branch (or vice versa). Noteworthy is the “hysteresis” and the fact that only an additional relaxation path creates stability. 相似文献
5.
For the first time, direct experimental evidence of a new mechanism for the quenching of fluorescence of organic ligands (L) in complex compounds with lanthanide ions (Ln3+) is obtained. By analogy with the mechanism of luminescence quenching upon pair interactions of Ln3+ ions in inorganic systems, this mechanism is called the cross-relaxation mechanism. The experiments are performed with complexes of Tb3+ with dianions of halogen-substituted fluoresceins (HSFs): 4,5-dibromo-and 4,5-diiodofluorescein, eosin B, eosin, erythrosin, and Rose Bengal in dimethyl sulfoxide. In accordance with this mechanism—exchange energy transfer, L2?(*S
1), Tb3+(7
F
6)→L2?(T
1), Tb3+(7
F
5, 4), allowed by the spin selection rules—an increase in the quantum yield of formation of the triplet state (ΦT) of a ligand L2? and a decrease in the quantum yield of fluorescence (Φfl) are found to take place upon complexation. The efficiency of this process amounts to ~1 in accordance with the equality Φfl+ΦT=1, valid for solutions of HSFs. The possibility of other processes leading to a similar effect, specifically, recharging of the system (as for complexes of HSFs with Eu3+ and 3+) is considered. An example of inductive resonance interactions in complexes of HSFs with Pr3+ is given. The manifestation of equilibrium between outer-sphere and inner-sphere complexes in the photophysics of complexes of metals with HSFs is discussed. 相似文献
6.
Laser-induced fluorescence of anisole as tracer of isooctane at an excitation wavelength of 266 nm was investigated for conditions relevant to rapid compression machine studies and for more general application of internal combustion engines regarding temperature, pressure, and ambient gas composition. An optically accessible high pressure and high temperature chamber was operated by using different ambient gases (Ar, N 2, CO 2, air, and gas mixtures). Fluorescence experiments were investigated at a large range of pressure and temperature (0.2–4 MPa and 473–823 K). Anisole fluorescence quantum yield decreases strongly with temperature for every considered ambient gas, due to efficient radiative mechanisms of intersystem crossing. Concerning the pressure effect, the fluorescence signal decreases with increasing pressure, because increasing the collisional rate leads to more important non-radiative collisional relaxation. The quenching effect is strongly efficient in oxygen, with a fluorescence evolution described by Stern–Volmer relation. The dependence of anisole fluorescence versus thermodynamic parameters suggests the use of this tracer for temperature imaging in specific conditions detailed in this paper. The calibration procedure for temperature measurements is established for the single-excitation wavelength and two-color detection technique. 相似文献
7.
Resonance Raman spectra (RRs) and quantum chemical calculations were used to investigate the photodissociation dynamics of diuron in S 2 state. The RRs indicate that the photorelaxation dynamics for the S 0 → S 2 excited state is predominantly along nine motions: the ring C = C stretch vibration ν 12 (1593 cm −1), Ph–N–H wag ν 14 (1517 cm −1), CO–N(CH 3) 2 stretch ν 23 (1365 cm −1) , CCH wag in plane/ring C = C stretch ν 24 (1297 cm −1) , ring CH rock in plane/ring deformation ν 27 (1233 cm −1), CCH wag in plane ν 29 (1151 cm −1), Ph–Cl (para) stretch ν 35 (1028 cm −1), Ph–N–H wag ν 37 (913 cm −1) and ring breath ν 44 (685 cm −1). Dissociation by Ph–Cl (para) cleavage at S 2 state directly or relaxation to T 2 state by internal conversion (S 2 → S 1) and intersystem crossing (S 1/T 2) is expected by ~250 nm irradiation based on the RRS, complete active space self‐consistent field, configuration interaction singles and time‐dependent density functional theory calculations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
We have measured the photoluminescence spectra of nanometric scale X 1-Y 2SiO 5:Eu x. The spectra were recorded at 15K and room temperature using site selective excitation by a dye laser in addition to conventional UV excitation. We found that at low temperature there is a pronounced excitation transfer from site 2→1. The transfer rate increases rapidly with increasing concentration and for x=0.7 no fluorescence from site 2 can be observed. Decaycurve measurement revealed this transfer process directly. The lifetimes of the 5Do levels of the two sites were also measured as a function of Eu 3+ concentration. The results show that the lifetimes of the 5D 0 level of site 2 decreases with increasing concentration. The mechanism of the excitation transfer is discussed. Wavelengths of the 5D 0→ 7D 0–4 transitions of the two sites were also tabulated. 相似文献
9.
We observed fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation of jet-cooled perylene- h 12 and perylene- d 12, and carefully examined the vibrational structures of the S 0 1 A g and S 1 1 B 2u states. We performed vibronic assignments on the basis of the results of ab initio calculation, and found that the vibrational energies in the S 1 state are very similar to those in the S 0 state, indicating that the potential energy curves are not changed much upon electronic excitation. We conclude that the small structural change is the main cause of its slow radiationless transition and high fluorescence quantum yield at the zero-vibrational level in the S 1 state. It has been already reported that the lifetime of perylene is remarkably short at specific vibrational levels in the S 1 state. Here, we show that the mode-selective nonradiative process is internal conversion (IC) to the S 0 state, and the ν 16( a g ) in-plane ring deforming vibration is the promoting (doorway) mode in the S 1 state which enhances vibronic coupling with the high-vibrational level ( b 2u ) of the S 0 state. 相似文献
10.
Fluorescence has recently been applied to the analysis of the molecular organization state of the polyene antibiotic amphotericin
B (AmB) in solution or in lipid membranes. The polyene chain of AmB monomer gives rise to two fluorescence emissions; S 1(2 1A g) → S 0(1 1A g) between 500 and 700 nm, S 2(1 1B u) → S 0(1 1A g) between 400 and 500 nm. However, Raman scattering might interfere with the S 2 → S 0 emission fluorescence due to the weak fluorescence quantum yield and close proximity to the exciting lines. In fact, we show
here that a change in the excitation wavelength results in a shift of three emission bands, an effect which excludes their
assignment to fluorescence. These bands originate from the water Raman at 3382 cm -1and AmB resonance Raman at 1556 and 1153 cm -1. As a consequence, some former conclusions on the molecular organization state of AmB should be reconsidered. 相似文献
11.
This study considers the effects of hydrostatic pressure on the line position and fluorescence lifetime τ for 5D 0 → 7F 2 transitions in GdVO 4: Eu 3+ nanocrystals. The results indicate that the pressure induced the red shift toward longer wavelengths for all the considered lines with different rate. The fluorescence lifetime τ nonlinearly decreases with pressure in the considered pressure range. High pressure induced the fluorescence lifetime τ that can be explained with a simple theoretical model. The measured line position and τ are in a satisfactory agreement with the theoretical calculations. 相似文献
12.
Emission and excitation spectra of p-benzoquinone have been measured in a partially translucent p-dichlorobenzene host matrix at different temperatures from 77 up to 323 K. Successive occurrence of the T 1(n,π ?) and T 2(n,π ?) phosphorescence and S 1(n,π ?) fluorescence has been observed for p-benzoquinone upon increasing temperature. The S 1–T 2 and T 2–T 1 energy separations determined from the temperature dependence of the emission intensities agreed well with those obtained from the locations of the T 1 and T 2 phosphorescence and S 1 fluorescence origins. Occurrence of the emission from S 1 and T 2 is brought by the thermal population from the T 1 state. The symmetries of the T 1 and T 2 states were determined to be B 1g and A u, respectively, based on the spectral data. 相似文献
13.
A photon echo induced exclusively by collisions of ytterbium atoms with buffer gas atoms has been observed at a 0 ? 1-type 1 S 0(6 s 2)- 3 P 1(6 s6 p) 174Yb transition. The polarization properties of a collision echo and the buffer gas density dependence of its intensity agree with theoretical predictions of a model of depolarizing collisions that takes into account the dependence of a relaxation matrix on the velocity of active particles. Thus, direct experimental evidence of the relaxation anisotropy due to depolarizing collisions has been obtained. 相似文献
14.
3‐(4‐Nitrophenylethenyl‐ E)‐NH‐indole ( 1 ), 3‐(4‐nitrophenyl ethenyl‐ E)‐ N‐acetylindole ( 2 ), and 3‐(4‐nitrophenylethenyl‐ E)‐ N‐benzenesulfonylindole ( 3 ) are relatively less fluorescent in organic solvents, with fluorescence quantum yield (Φ f) in the range of 0.002 to 0.066 depending on the solvent polarity. However, in bovine serum albumin (BSA)‐phosphate buffer, the fluorescence of these compounds gets drastically enhanced with Φ f in the range of 0.21 to 0.67, depending on the substituent on the indolic nitrogen atom. Additionally, linear increase in the fluorescence intensity of 2 and 3 occurs on increasing the BSA concentration. These fluorescence properties together with the neutral, hydrophobic nature of these compounds make these fluorophores good fluorescence probe for studying the micropolarity of proteins like BSA and in general the ligand–protein interactions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
15.
Highly resolved fluorescence and S 1←S 0 absorption spectra of some phenanthrolines in n-alkane matrices were obtained at 77 K. The vibrational analysis of the spectra was carried out. Mirror symmetry distortions of the fluorescence and absorption spectra were attributed to vibronic coupling between 1(π, π 1) states. It was shown that vibronic mixing of S 1(π, π 1) and S 2(π, π 1) states occurs in phenanthroline molecules with S 1-S 2 energy gap not exceeding 3000 cm -1 (i.e., 4,7-, 1,7- and 1,10-Phen), whereas in other phenanthrolines the coupling of S 1 and S 3(π, π 1) plays a dominant role. Fluorescence quantum yields of phenanthroline liquid solutions were measured. Changes of luminescence efficiencies due to the change of the polarity of the media point to a weak coupling of the lowest 1(π, π 1) and 1(n, π 1) states. 相似文献
16.
The results of the experimental investigation of the radiation amplification due to the stimulated four-photon parametric process in potassium vapor are reported. Two cells with active medium (an oscillatoramplifier system) are used in the experiments. The dominating role of IR radiation 6 S → 5 P (3.66 µm) in the amplification of violet radiation 5 P → 4 S (0.4 µm) generated due to the parametric process at two-photon excitation 4 S → 6 S is shown. This role is conditioned by optically pumped stimulated emission (OPSE). Optical conditions for the amplification of a seed radiation are determined in accordance with their intensity and the buffer gas (He) pressure. The problem of the image conversion from the IR to a visible one with quantum efficiency above 100% is discussed. 相似文献
17.
The cascade decay of the 6 S(4 D) levels of the potassium atom, 6 S(4 D)-5 P-5 S(3 D)-4 P, following two-photon excitation of potassium vapor (4 S-4 P-6 S) is investigated experimentally. The dependences of 11 resonant IR line intensities on potassium and buffer gas densities are presented. It is shown that the presence of buffer gas leads to collisional redistribution of radiation, causing suppression of some lines and production of new ones. 相似文献
18.
By the spectral and kinetic characteristics of the luminescence of vapors of polyatomic molecules (anthracene, anthraquinone, fluorenone) initiated by selective IR multiphoton excitation (IR MPE) of molecules in the ground electronic state S
0 the relaxation processes proceeding under vibrational excitation of molecules to energies exceeding the energies of the lower excited electronic states have been investigated. The changes in the spectral and kinetic characteristics with increasing CO 2 laser energy density and vapor P
v and foreign gas pressure P
FG are analyzed. They are similar to the characteristics obtained for normal fluorescence of these molecules with changing vibrational energy E
vib content. On the basis of experimental data and model calculations it has been concluded that at the laser radiation densities used in the case of IR MPE the molecules reach energies considerably exceeding the energies of the electronic levels. It is shown that a nonadiabatic connection between the electronic states leads to the population of mixed electronic states isoenergetic to the vibrational levels of the ground electronic state and to emission of delayed luminescence spectrally identical to the normal luminescence of these molecules. It has been found that when high vibrational levels are populated, new relaxation channels, such as reverse electron relaxation, emission from high vibrational levels of the ground electronic state, and multiquantum vibrational energy transfer at collisions leading to a rapid establishment of vibrational equilibrium become important. 相似文献
19.
The relaxation times of excited states of arsenic dopant in germanium at cryogenic temperatures T < 15 K have been experimentally studied by the optical pump-probe method using radiation of a free-electron laser. Two variants of the excitation of impurity centers have been used in the experiment: (i) from the 1s(A1) ground state of the dopant and (ii) from the 1s(T2) first excited state having a finite thermal population. In the former variant, it has been shown that the decay times of the 2p0 and 3p± states are about 0.8 and 0.6 ns, respectively. In the latter variant, a single measurement can simultaneously provide the relaxation times of two 2p± and 1s(T2) states about 0.6 and no more than 0.16 ns, respectively. The data obtained have indicated the possibility of forming population inversion and the gain of terahertz radiation at the 2p± → 1s(T2) and 2p0 → 1s(T2) transitions at the optical excitation of the mentioned impurity centers. 相似文献
20.
A cw dye laser beam, tuned near the Cs 8761 Å resonance (Cs 1(6P ) → Cs 1(6D ) transition) is focused into a Cs vapor. At a Cs density higher than 5 × 10 15 cm -3, we observe a greater 6P population when the laser is on resonance than when it is off resonance. However, at a lower Cs density, the reverse is observed. This phenomenon is explained as due to the preferential excitation transfer process: Cs 1(6D ) + Cs(6S ) → Cs 1(6P) + Cs 1(6P), and the corresponding cross secti on is estimated to be (1.5 +1.5-0.7) × 10 -14 cm 2 by fitting the experimental results to an approximate rate-equation analysis. 相似文献
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