共查询到20条相似文献,搜索用时 15 毫秒
1.
E. I. Sagun é. I. Zenkevich V. N. Knyukshto A. M. Shulga N. V. Ivashin 《Optics and Spectroscopy》2010,108(4):553-570
The directional self-assembly of nanosized, structurally organized pentads that include five tetrapyrrole macrocycles and
are based on the two-point coordination interaction of two covalently bound dimers of Zn porphyrins (homo-and heterodimers)
with molecules of either the free base or the Cu complex of tetrametapyridyl-substituted porphyrin extra ligand is implemented
in methylcyclohexane at 295 K. Using the method of the density functional theory (DFT) in the B3LYP/6-31g(d) approximation, the geometry of the pentad is fully optimized and the main factors that determine its redox properties are
determined. The energies of the lowest excited states of the pentad are calculated by the ZINDO/S method, and it is shown
that the occurrence of identical molecules in the system facilitates the formation of excitonic states with different contributions
from the charge-transfer component. The directional energy transfer and the photoinduced electron transfer, which leads to
the formation of a low-lying charge-transfer state (CT state), are studied and the rate constants of these two processes are
determined (k
ET ∼ 1011 s−1 and k
PET ≈ (1.8−6.0) × 109 s−1, respectively). The strong effect of the temperature of the solvent on the efficiency of relaxation processes in pentad complexes
under study is revealed and studied. Roles played by the low-lying CT state and d-π exchange effects (the Cu-contained pentad) in fluorescence quenching of pentad complexes are determined. 相似文献
2.
Oxygen quenching of excited triplet and singlet states of gas-phase anthracene and its derivatives that have similar energies
of the lower triplet levels but widely different oxidation potentials (0.44 < Eox < 1.89 V) was studied. Quenching rate constants for singlet (kSO2) and triplet (kTO2) states in addition to the fraction of oxygen-quenched singlet and triplet states qS
1(T1O2 were determined from the decay rates, fluorescence intensities, and delayed fluorescence as functions of oxygen pressure.
It was found that kSO2 values vary from 2·104 (9,10-dicyanoanthracene) to 1.2·107 sec−1·torr−1 (anthracene, 9-methylanthracene, 2-aminoanthracene) and kSO2 values from 5·102 to 1·105 sec−1·torr−1. The kSO2 values for anthracene, 9-methylanthracene, and 2-aminoanthracene, which have fast rates of interconversion from S1 to T1, are close to the rate constants for gas-kinetic collisions and are independent of the oxidation potentials (Eox). The quenching rate constants kSO2 for the other anthracene derivatives and kTO2 for all studied compounds decrease with increasing free energy of electron transfer ΔGET, which indicates the important role of charge-transfer interactions in the oxygen quenching of singlet S1- and triplet T1 states.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 36–42, January–February, 2008. 相似文献
3.
Using the methods of time-resolved absorption spectroscopy, we have investigated the features of quenching, by molecular oxygen, of the excited triplet states of water-soluble 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphyrin (H2TMPyP) and 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (H2TSPP) in water–ethanol solutions. It has been revealed that for both compounds the rate constant of quenching of the triplet states increases with increasing viscosity of the medium. Quenching of the excited triplet states of the dissociated (in water) and undissociated (in ethanol) forms of water-soluble porphyrins occurs with a different efficiency, and the rate constant of quenching the triplet states by molecular oxygen k T thereby is higher for the dissociated form. It has been shown by means of mathematical modeling that the experimental results obtained can be described in terms of the change in the rate constants of intracomplex transitions in the porphyrin–oxygen collisional complex at varied solution viscosity and their difference for the dissociated and undissociated forms of water-soluble porphyrin. 相似文献
4.
Excited singlet (S
1) and triplet (T
1) state quenching by O2 and by (O2 + H2O) gas-vapor mixtures was studied in the gas phase for polycyclic aromatic hydrocarbons (PAHs, anthracene, 2-aminoanthracene,
pyrene). Addition of water vapor is shown not to influence quenching of both fluorescence and delayed fluorescence of PAHs
by oxygen. The role of complexes stabilized by charge transfer and hydrogen bonds in quenching the excited states of PAHs
by atmospheric gases was analyzed.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 342–348, May–June, 2009. 相似文献
5.
S. L. Bondarev V. N. Knyukshto S. A. Tikhomirov A. N. Pyrko 《Optics and Spectroscopy》2003,94(6):928-933
The spectral-luminescent properties and electronic-level structure of a derivative of oxotetrahydrobenzo[c]phenanthridine—3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-one
(DTP)—in polar and nonpolar solutions are studied by the luminescence and picosecond spectroscopy techniques at 293 and 77
K. It is shown that DTP exhibits ππp* fluorescence only in polar proton-containing methanol, ethanol, and n-propanol and that this fluorescence is associated with a chromophore + alcohol complex. Solutions of DTP in n-propanol and the nonpolar mixture methylcyclohexane + toluene (6:1) at 77 K display ππp* phosphorescence with a quantum yield
ΦPh=0.1, a lifetime τPh=1.9 s, and a frequency of the 0-0 transition equal to 21550 cm−1. The fact that DTP fluorescence is absent in aprotic solvents and exists in alcohols is explained by the inversion of the
energy levels of the S
ππ* and T
n
π* states, as a result of which the energy level of the fluorescing S
ππ* state in alcohol becomes the lowest. The picosecond spectra and kinetics of the inducedS
n
(ππ*) ← S
1(π π*) and T
k
(ππ*) ← T
1(ππ*) absorption made it possible to estimate the lifetime of the S
1(ππ*) state of DTP in n-propanol at 293 K (20±10 ps) and the position of the triplet-triplet absorption peak (495 nm).
__________
Translated from Optika i Spektroskopiya, Vol. 94, No. 6, 2003, pp. 993–998.
Original Russian Text Copyright ? 2003 by Bondarev, Knyukshto, Tikhomirov, Pyrko. 相似文献
6.
K. Kamiyama D. Shiomi S. Hase M. Nishizawa K. Sato M. Kozaki K. Okada T. Takui 《Applied magnetic resonance》2000,19(1):45-57
A crystal-engineering approach to organic ferrimagnets is reported. Coulombic energy between an anionic biradical withS = 1 and a cationic monoradical withS = 1/2 can be utilized as a driving force of cocrystallization of open-shell molecules with different spin quantum numbers,
leading to organic salt ferrimagnets. In this study, 3,5-substituted phenol and benzoic acid derivatives of nitronyl nitroxide
biradicals were synthesized as an ionizableS = 1 component of organic salt ferrimagnets. The molecular ground states of the biradicals in the neutral state were examined
by continuous wave electron spin resonance (ESR) spectroscopy and static paramagnetic susceptibility measurements in the solid
state. The molecular ground state of the phenol derivative was found to be triplet (S = 1) with the singlet-triplet energy gap of ΔE/kB ≈ 25 K, indicating that the biradical can be a building block of organic salt ferrimagnetics. The benzoic acid derivative
was found to have a singlet (S = 0) ground state (ΔE/kB
≧ −5 K), exemplifying thatmeta-(3,5)-linkage of unpaired electrons in π-aromatic rings does not necessarily give a triplet ground state for heteroatomic-substituted
π conjugation. The molecular ground states of the biradicals determined in the ESR experiments were confirmed by the susceptibility
in the solid state. 相似文献
7.
V. N. Knyukshto E. I. Sagun A. M. Shul’ga S. M. Bachilo É. I. Zen’kevich 《Journal of Applied Spectroscopy》1998,65(4):487-491
For the first time it is discovered that the mono- and dimesoaryl substitution in porphyrins (free bases and their Zn-complexes)
as well as the formation of chemical dimers with a phenyl spacer are manifested in the abrupt reduction (300–500 times less)
of the lifetime of T1-states at 295 K and are not accompanied by enhancement of the nonradiative deactivation of the S1-state. These effects are associated with the nonlinear dynamic deformations of the π-conjugate macrocycle in the T1-state due to torsional oscillations of a phenyl ring about a single C–C-bond in sterically complicated porphyrins.
To whom correspondece should be addressed.
Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072,
Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 471–475, July–August, 1998. 相似文献
8.
We study the temperature dependence of the radiative deactivation of triplet states of Pdand Pt-porphin molecules in n-alkane matrices in the temperature range 4.2–210 K. The nature of the thermally activated “hot” lines that are observed in
phosphorescence spectra of Pdand Pt-porphin is discussed in detail. We show that, because of the degeneracy lifting of the
triplet state T
1, 2 in the crystal field of n-alkane matrices, lines of the transitions T1 → S
0 and T
2 → S
0 are spectrally spaced and, in all cases, the T
2 state is the first state that is activated with increasing temperature. We analyze the dependences of the T
2-T
1 splitting on the chelated metal ion and the type of the matrix. The possibility of measuring cryogenic temperatures with
molecular thermometers that use the thermochromic properties of Pdand Pt-porphin in n-alkane matrices is discussed. 相似文献
9.
In terms of the adiabatic theory of interactions, we consider the results of the theoretical estimation of the rate constants
K
ST
of the nonradiative intersystem crossing conversion S
1(ππ*) ⇝ T
1
S
(ππ*) for nine aromatic molecules containing 10–14 carbon atoms and one or two heavy (many-electron) oxygen or chlorine atoms. 相似文献
10.
V. A. Svetlichnyi 《Russian Physics Journal》2009,52(7):661-667
duration ranging from femtoseconds to nanoseconds has been simulated. The effect of the absorption from excited singlet and
triplet states on the transmissivity of the medium under two-photon excitation has been investigated. It has been shown that
in a medium excited by monopulses, the S
1→ S
n
and T
1→ T
m
absorption makes a considerable contribution to the total nonlinear absorption of the medium only for nanosecond pulse durations.
When a medium is excited by a sequence of femtosecond pulses with a repetition frequency of some tens of megahertz, significant
additional nonlinear absorption can arise only due to T
1→T
m
transitions that occur due to accumulation of molecules in triplet states. This effect should be taken into account in determining
the cross-section for two-photon absorption in dyes and also in developing radiation intensity limiters for femtosecond lasers. 相似文献
11.
S. L. Bondarev 《Journal of Applied Spectroscopy》1997,64(1):1-15
A review of data on the photophysics of carotenoids is presented. Results of investigations of spectroscopic, temporal, and
energy parameters of excited S1 and S2 singlet states of β-carotene and related compounds are critically examined. These states give rise to extremely high probabilities
(1011–1013 sec−1) of radiationless deactivation of the electronic excitation energy in carotenoids. Results of investigations of photophysical
properties of triplet states of carotenoids are considered mainly from the standpoint of quenching of singlet oxygen and triplet
states of organic molecules by carotenoids.
Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 5–19, January–February, 1997. 相似文献
12.
O. Krumkacheva M. Tanabe S. Yamauchi M. Fedin S. R. A. Marque E. Bagryanskaya 《Applied magnetic resonance》2012,42(1):29-40
The triplet states of deoxybenzoin (DOB) and benzophenone (BP) molecules in randomly methylated β-cyclodextrin (CD) cavity
are studied by time-resolved (TR) and pulse electron paramagnetic resonance (EPR). The observed TR EPR spectrum of DOB in
β-CD at 30 K is close to the spectrum measured in polar solvent trifluoroethanol, revealing strong hydration by water molecules.
At the same time, TR EPR spectrum of BP in β-CD corresponds to nonpolar surrounding of the CO-group. The electron spin relaxation
times T
1 and T
2 of triplet BP at 30 K measured by pulse EPR are found to be different in β-CD compared to nonpolar toluene glass. The observed
increase of T
2 by up to a factor of four in β-CD is caused by the lower vibration amplitude of CO-bond of BP due to the confinement in β-CD.
The influence of β-CD with covalently attached nitroxide on the triplet states of DOB and BP is principally different: the
excited triplet states could not be observed by TR EPR due to the efficient quenching of the excited states by nitroxide. 相似文献
13.
pp and πd scattering and pp →πd reaction processes at incident proton laboratory energies T
L
≤ 1 GeV are studied in the framework of πNN dynamics. For this purpose three-body calculations are performed with the πN interaction in the P
11, P
33, S
11 and S
31 states and NN forces in the 3
S
1 -3
D
1, 1
S
0, and 3
P
2 states. In addition, the backward-going pion contribution at the πNΔ vertex, the πN-ρN coupling, the heavy-meson exchanges in the NN → NN driving term, and the effect of the off-shell structure in the πN-ρN P
33 interaction are taken into account.
Received March 28, 1994; revised July 29, 1994; accepted for publication August 31, 1994 相似文献
14.
We have pioneered a method of determining the rate constant of quenching of the excited electronic states of molecules by
molecular oxygen from measurements of the kinetics of photosensitized luminescence of singlet molecular oxygen (lδg). The method can be used in the case where the lifetime of the excited electronic state in an air-saturated solution is comparable
with or larger than the luminescence time of the singlet molecular oxygen in the given solvent. It is shown that this situation
is implemented on quenching, by molecular oxygen, of the excited triplet states associated with the biopolymers of tetrapyrrole
molecules in aqueous (H2O and D2O) solutions.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 401–404, May–June, 2000. 相似文献
15.
V. A. Chernyavsky P. P. Pershukevich I. K. Shushkevich E. A. Makarova K. N. Solovyov 《Journal of Applied Spectroscopy》2009,76(5):672-677
Transient absorption spectra of tetraazaporphine and substituted derivatives of tetraazachlorin and tetraazabacteriochlorin
were obtained upon picosecond excitation with various probe pulse delay times in order to resolve the open question about
the reasons for fluorescence quenching in tetraazaporphine hydrogenated derivatives. The quantum yield of triplet state T
1 formation has been estimated. It has been shown that in all investigated cases radiationless de-excitation of the fluorescent
level S
1 occurs by two channels: S
1 ⤳ T
1 and S
1 ⤳ S
0, the latter being predominant. As the S
1 level becomes lower, the transition rate for this channel increases. For tetraazaporphine and its derivatives, a quasi-photochemical
mechanism is proposed that accounts for the anomalous efficiency of the S
1 ⤳ S
0 channel in the dissipation of the electronic excitation energy. 相似文献
16.
V. N. Knyukshto É. I. Zen'kevich E. I. Sagun A. M. Shul'ga S. M. Bachilo 《Journal of Applied Spectroscopy》1999,66(4):588-592
It is shown that at 295 K in meso-orthonitrophenyl-substituted octaethylporphyrins and their chemical dimers the steric interactions
of the nitro-group and the volume substituents at β-positions of the pyrrole rings favor direct overlapping of molecular orbitals
in a donor-acceptor pair. The efficient quenching of fluorescence of the nitroporphyrins in toluene is attributed to direct
nonadiabatic electron transfer from the S1-level of a porphyrin to the lower-lying state with charge transfer by the “through-space” mechanism. Quenching of the T1-states is related with heat-stimulated transmission to the higher-lying states with charge transfer of the ion-radical pair
as well as with enhancement of the probability of the nonradiative T1→S0-transition.
To whom correspondence should be addressed.
Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998.
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 531–535, July–August, 1999. 相似文献
17.
By the quenching of the delayed fluorescence (DF) of anthraquinone vapors by aliphatic amines (diethylamine, dibutylamine, cyclohexylamine) and pyridine the photoinduced processes proceeding with the participation of vibrationally excited triplet molecules of anthraquinone have been investigated. The DF quenchingrate constants K
q varying from 1·106 sec–1·torr–1 in mixtures with diethylamine to 7·103 sec–1·torr–1 in mixtures with pyridine have been estimated. A correlation between the values of K
q and the ionization potentials of foreign gases confirming the important role of interactions with charge transfer in the quenching of triplet molecules in the gas phase has been established. The influence of other relaxation processes on the DF quenching is considered. It is shown that the intermolecular vibrational relaxation in the T
1 triplet state leading to the establishment of relaxation equilibrium at a vibrational temperature T
vib considerably increasing the medium temperature is the fastest process among the biomolecular processes (rate constants K
col
V > 106 sec–1·torr–1 > K
q). The values of T
vib and the vibrational energies E
vib of the triplet molecules after the energy exchange in the collisional complex have been estimated. It has been concluded that the photochemical reaction yield is determined by the intermolecular processes proceeding in the T
1 state at a vibrational equilibrium characterized by high values of T
vib. The influence of E
vib of triplet molecules on the DF quenching rates at a photoinduced electron transfer is considered. 相似文献
18.
C.M. Marian F. Schneider M. Kleinschmidt J. Tatchen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):357-367
Electronic spectra of uracil in its diketo (lactam) form and five enol (lactim) tautomeric forms have been investigated by
means of combined density functional and configuration interaction methods. We have simulated the effects of hydrogen bonding
with a protic solvent by recomputing the spectrum of uracil in the presence of two, four, or six water molecules. Geometries
of the electronic ground state and several low-lying excited states have been optimized. Spin-orbit coupling has been determined
for correlated wavefunctions employing a non-empirical spin-orbit mean-field approach. In accord with experiment, we find
the diketo tautomer to be the most stable one. The calculations confirm that the first absorption band arises from the 1( π↦π*) S
0↦S
2 excitation. The experimentally observed vibrational structure in this band originates from a breathing mode of the six ring.
Complexation with water molecules is seen to cause a significant blue shift of n↦π* excitations while leaving π↦π* excitations nearly uninfluenced. Computed radiative lifetimes are presented for the experimentally known weak phosphorescence
from the π↦π* excited T1 state. Among the uracil lactim tautomers, one is particularly interesting from a spectroscopic point of view. In this tautomer,
the π↦π* excitation gives rise to the S1 state.
Received 18 February 2002 / Received in final form 5 June 2002 Published online 13 September 2002 相似文献
19.
E. A. Gastilovich V. G. Klimenko L. V. Volkova R. N. Nurmukhametov 《Optics and Spectroscopy》2011,111(5):766-775
In the nonadiabatic approximation, we study how intramolecular interactions affect the nonradiative energy degradation T
1
s
↝ S
0 of triplet sublevels s of the lowest triplet state of the dibenzo-p-dioxin molecule. We consider the role played in the degradation by the shape of promoting high- and low-frequency vibrational
modes and by spin-orbit interactions separately in the carbon backbone of the molecule and in heteroatoms (oxygen). We find
that σ-electrons of oxygen that correspond to the lone pair and to valence electrons play different roles in the nonadiabatic
interaction. 相似文献
20.
Photoinduced effects on the electron spin polarization (ESP) in the lowest excited triplet (T1) states of porphyrins (PORs) and phthalocyanines (PCs) have been observed with a two-color time-resolved (TR) electron paramagnetic resonance (EPR) technique in a glassy matrix at low temperatures. On single-color excitation with the wavelengths of the ground state absorptions of PORs and PCs, polarized EPR spectra due to the corresponding T1 state were observed. The polarization patterns match well with interpretation as anisotropic intersystem crossing (ISC) induced by the spinorbit coupling between the singlet excited (S1) and the triplet states. In contrast, two-color excitation led to a change of the phase of the T1 state polarization pattern to the opposite. The observed ESP in the T1 state resulting from the excitation to the upper triplet state (T n ) was interpreted in terms of anisotropic ISC between the T n and S1 states. From the analysis of the ESP, changes in the quantum yields of the reverse ISC processes were determined at different temperatures. The results could be best interpreted by the existence of thermal pathways with small activation energy in the relaxation processes. 相似文献