Determination of the rate constant of oxygen quenching of the excited states of molecules from the singlet oxygen luminescence

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 (^lδ_g). 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.     

Fluorescence quenching of water-soluble porphyrins by molecular oxygen

Quenching by molecular oxygen of excited states of water-soluble anionic 5,10,15,20-tetarkis-(4-sulfonatophenyl)-porphyrin (H₂TSPP) and cationic 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphyrin (H₂TMPyP) in aqueous ethanol was investigated. It was found that fluorescence quenching of dissociated (in water) and undissociated (in ethanol) forms of H₂TSPP was diffusion-controlled and occurred at distances close to contact ones (0.5–0.8 nm). Fluorescence of the dissociated form of H₂TSPP was quenched with rate constant k_S that was 1.7 times greater than that of the undissociated form. It was proposed that this was due to a decrease in the porphyrin molecule oxidation potential on going from the undissociated to the dissociated form. It was shown that the most probable reason for the dramatic increase in the rate constant of the fluorescence quenching of H₂TMPyP in water compared with that of H₂TSPP was the low-lying intramolecular charge-transfer state typical of H₂TMPyP. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 170–176, March–April, 2008.     

Radiative and Nonradiative Deactivation of the 1Δ g State of Molecular Oxygen in Solutions of Saturated Hydrocarbons

The luminescence of singlet molecular oxygen (¹ _g or ¹O₂) caused by the ¹ _g ³ _g ^– transition in liquid saturated hydrocarbons from n-hexane to n-undecane is investigated. A model of quenching of the ¹ _g state of the oxygen molecule by the CH oscillations of the molecules of solvents is proposed, in which the rate constant of the nonradiative deactivation (k _nr) depends strongly on the average distance between the ¹O₂ and CH groups of the solvent. This experimental dependence can adequately be described by an exponential function with the distance parameter R ₀ = 0.15 , which indicates that the acceleration of quenching with the solvent density is a result of larger overlapping of the electron orbitals of oxygen and the CH groups. The detected increase in k _nr with temperature can also be explained qualitatively well within the framework of the model suggested. It is shown that the radiative rate constant (k _r of the ¹ _g ³ _g ^– transition does not depend on the distance between the ¹O₂ and CH groups and its change in a number of hydrocarbons is related to macroscopic parameters, in particular, the polarizability of the solvent.     

Collisional quenching and depolarization of the fluorescence of the 2,5-diphenyloxazole and 2-phenylbenzoxazole vapors by oxygen

We have measured the constants of collisional quenching and depolarization of the fluorescence of a number of derivatives of 2,5-diphenyloxazole and 2-phenylbenzoxazole in a gas phase by oxygen. The probabilities of quenching and orientation randomization of a single collision are determined. It is shown that quenching is significantly influenced by the electron-donor properties of substituents.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 43–47, January–February, 2005.     

Mechanism of singlet-oxygen induced delayed fluorescence of bacteriopheophytin in laser excitation

The relative intensity of photosensitized phosphorescence of singlet oxygen (¹O₂) at 1270 nm (L₁₂₇₀) and¹O₂-induced delayed fluorescence (L_df) of bacteriopheophytin a (BPh) (770 nm) in air-saturated solutions of BPh in hexafluorobenzene in excitation by 337-nm pulses of a nitrogen laso is investigated. It is established that L_df≪L₁₂₇₀. The ratio of the initial intensity of delayed fluorescence and phosphorescence of¹O₂(L_df)₀/(L₁₂₇₀)₀ changed from 0.02 to 0.30 as a function of the energies of laser pulses (2.5–5.0 mJ/cm¹) and the BPh concentration (6–18 μM). As the index of quantum efficiency of the delayed fluorescence, the authors used the coefficient

Role of charge-transfer complexes in oxygen quenching of excited states of anthracene derivatives in the gas phase

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 < E_ox < 1.89 V) was studied. Quenching rate constants for singlet (k_S^O2) and triplet (k_T^O2) states in addition to the fraction of oxygen-quenched singlet and triplet states q_{S 1}(T₁^O2 were determined from the decay rates, fluorescence intensities, and delayed fluorescence as functions of oxygen pressure. It was found that k_S^O2 values vary from 2·10⁴ (9,10-dicyanoanthracene) to 1.2·10⁷ sec⁻¹·torr⁻¹ (anthracene, 9-methylanthracene, 2-aminoanthracene) and k_S^O2 values from 5·10² to 1·10⁵ sec⁻¹·torr⁻¹. The k_S^O2 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 (E_ox). The quenching rate constants k_S^O2 for the other anthracene derivatives and k_T^O2 for all studied compounds decrease with increasing free energy of electron transfer ΔG_ET, which indicates the important role of charge-transfer interactions in the oxygen quenching of singlet S_1- and triplet T₁ states. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 36–42, January–February, 2008.     

Excitation dependent quenching of luminescence in LED phosphors

Droop, the decrease of efficiency with increased power density, became a major topic with InGaN LEDs, after its introduction in 2007. This paper provides insight into droop in localized center luminescence phosphors, exemplified here by Eu²⁺ doped materials. This topic is of increasing importance, as high brightness blue LEDs have reached outputs >1 W/mm². The nonlinearities in phosphor quantum efficiency result in drive‐dependent color point shift and reduction of overall efficiency of phosphor converted white LEDs which utilize Eu²⁺ activated phosphors. The efficiency quenching can be traced back to two processes, well‐known in laser physics, excited state absorption or/and cross relaxation by Foerster/Dexter transfer. Both processes lead to reduction in phosphor efficiency, but they can be differentiated. Understanding the root cause of efficiency quenching opens ways to minimize the practical consequences. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Gas-phase photoreactions of anthracene, 2-aminoanthracene,and pyrene with oxygen and water vapors

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.     

Anomalies in oxygen-induced quenching of electronically excited states of 4,4′-bis[2-(1,3)-benzoxazol-2-yl)ethenyl]biphenyl in the vapor phase

From oxygen-induced quenching of polarized fluorescence of 4,4′-bis[2-(1,3-benzoxazol-2-yl)ethenyl]biphenyl, we have observed structural transformation in electronically excited molecules with retention of fluorescent capability, initiated by collisions with oxygen. Replacing two hydrogen atoms with fluorine in the ortho positions of the diphenyl moiety of the molecule leads to absence of quenching upon collisions with oxygen molecules, owing to the electronegative properties of fluorine atoms. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 902–905, November–December, 2008.     

冷射流方法脱除单重态氧气流中的水汽

为提高化学氧碘激光性能,分别使用-117 ℃乙醇、-110 ℃氟里昂和-45 ℃质量分数为50%过氧化氢冷射流进行单重态氧气流中的水汽脱除实验。实验结果表明：这3种冷射流的除水效果并不显著,乙醇基本上没有任何脱水效果,氟里昂和过氧化氢仅可以将水汽含量分别降低至原来的约1/5和1/4;乙醇和氟里昂因极易挥发而对气流产生严重干扰,并不适合用于除水;只有难挥发的过氧化氢才是合适的候选。     

冷射流方法脱除单重态氧气流中的水汽

为提高化学氧碘激光性能,分别使用-117 ℃乙醇、-110 ℃氟里昂和-45 ℃质量分数为50%过氧化氢冷射流进行单重态氧气流中的水汽脱除实验。实验结果表明:这3种冷射流的除水效果并不显著,乙醇基本上没有任何脱水效果,氟里昂和过氧化氢仅可以将水汽含量分别降低至原来的约1/5和1/4;乙醇和氟里昂因极易挥发而对气流产生严重干扰,并不适合用于除水;只有难挥发的过氧化氢才是合适的候选。     

JSOG中水蒸汽含量的模拟计算

氧碘化学激光（简称 COIL）系统中,水是影响激光功率输出的最重要的原因之一。气流中的水不仅对激发态碘原子有严重的猝灭作用,另外对碘分子解离、超音速流动特性也有很坏的负面作用。单重态氧发生器的BHP（Basic Hydrogen Peroxide ）溶液是最主要的水蒸汽源。利用传质模型对射流式单重态氧发生器（简称JSOG）中产生的水蒸汽进行了计算,所得的数值结果与实验测量结果基本相符。根据模拟结果,对发生器的设计及实验条件进行了优化。     

JSOG中水蒸汽含量的模拟计算

 氧碘化学激光（简称 COIL）系统中，水是影响激光功率输出的最重要的原因之一。气流中的水不仅对激发态碘原子有严重的猝灭作用，另外对碘分子解离、超音速流动特性也有很坏的负面作用。单重态氧发生器的BHP（Basic Hydrogen Peroxide ）溶液是最主要的水蒸汽源。利用传质模型对射流式单重态氧发生器（简称JSOG）中产生的水蒸汽进行了计算，所得的数值结果与实验测量结果基本相符。根据模拟结果，对发生器的设计及实验条件进行了优化。     

Statistical Meaning of the Excited-State Quenching Probability Found by a Fluorescence Depolarization Method

It is shown that the probability of quenching the excited electronic state of complex molecules, which is obtained from the vapor fluorescence depolarization, is averaged over the configurations of collisions with the quencher molecules with a collisional chaotization weight factor, i.e., it is transformed by this factor. The conditions under which this probability is close to the conventional one averaged only over the configurations of collisions are discussed. __________ Translated from Zhurnal Prikaldnoi Spektroskopii, Vol. 72, No. 4, pp. 563–564, July–August, 2005.     

Packing of phospholipid vesicles studied by oxygen quenching of Laurdan fluorescence

Steady-state fluorescence oxygen quenching experiments were performed on phospholipid vesicles where 2-dimethylamino-6-lauroylnaphthalene (Laurdan) was inserted. The quenching efficiency was found to be much higher in vesicles in the liquid-crystalline phase with respect to the gel phase, by a factor of about 50. Since the oxygen solubility in the two phospholipid phases can differ at most by a factor of 4 based on literature values, we concluded that oxygen diffusion must be responsible for the great difference in the quenching efficiency. A relatively high quenching efficiency was also found in vesicles composed of equimolar gel and liquid-crystalline phospholipids. Simulations were performed using the linear superposition of the properties of the pure phases to demonstrate that, in the case of vesicles composed of coexisting phases, the diffusional properties of oxygen in each phase are largely modified by the presence of the other. The addition of 10 mol% cholesterol to the gel phase rendered Laurdan fluorescence approximately as quenchable as in the equimolar mixture of the two phases. This result points out that molecules such as cholesterol, which introduce packing defects in the bilayer, favor oxygen diffusion. From the oxygen quenching experiments and using the properties of generalized polarization, the rate of Laurdan dipolar relaxation can be estimated.Abbreviations used Laudran 2-dimethylamino-6-lauroylnapthalene - DLPC dilauroylphosphatidylcholine - DMPC dimyristoylphosphatidylcholine - DPH 1,6-diphenyl-1,3,5-hexatriene - DPPC dipalmitoylphosphatidylcholine - TNS p-tofuidinyl-6-naphthalene sulfonic acid - PBS phosphate-buffered saline solution - GP generalized polarization - NMR nuclear magnetic resonance - EPR electron paramagnetic resonance     

Analysis of fluorescence quenching of pyronin B and pyronin Y by molecular oxygen in aqueous solution

The fluorescence quenching of pyronin B and pyronin Y molecules by molecular oxygen in aqueous solution was studied by using steady-state and time-resolved fluorescence and UV-Vis absorption spectroscopy techniques. In order to understand the quenching mechanism, fluorescence decays, absorption and fluorescence spectra of the probes were recorded as a function of the oxygen concentration and temperature. The quenching was found to be appreciable and shows positive deviation in the Stern-Volmer representation obtained from the fluorescence intensity ratio. Fluorescence quenching constants (k_q) were calculated from the τ_o/τ vs. [Q] plots having linear correlation and compared with calculated diffusion-controlled rate constants (k_diff) values. Experimental results were in good agreement with the simultaneous dynamic and static quenching model.     

Quenching of the triplet state of tetrapyrrole molecules by Ni-, Ag-, and Fe-porphyrins and formation of excited complexes and photoproducts

Using the method of pulse photolysis, we studied the quenching of the triplet state (TS) of a number of tetrapyrrole molecules by complexes of Ni-, Ag-, and Fe-porphyrins in liquid solutions at a temperature of ∼298 K under the conditions where the kinetics are markedly affected by the triplet-triplet annihilation of the molecules of energy donors. In the analysis of experimental data, derivatives for the time dependences of the optical density of the triplet-triplet absorption were determined. The triple-triplet annihilation process was considered for the case of the formation of excited a triplet-triplet complexes of two molecules in the triplet state. A procedure of determining the rate constant for the quenching of the triplet state by foreign molecules (K_q) under the effect of such triplet-triplet annihilation process is proposed and the values of K_q are obtained. For some donor-quencher pairs it is found that the kinetics of the triplet-state deactivation are affected by the formation of short-lived particles with lifetimes both shorter and longer than the triplet-state lifetimes. The conclusion is drawn that such particles are respectively the excited complexes of interacting molecules or ion radicals formed from such complexes in polar solvents. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 296–300, May–June, 2000.     

Determination of the Dipole Moments of Excited Complexes of Polar Compounds in Proton-Donor Solvents by the Quenching of their Fluorescence

A method of determining the permanent dipole moment of polar compounds in the excited S₁ state by the dependence of the rate of radiationless conversion of the energy of this state on the polarity of the solvent (medium) is proposed. The method was used for determining the dipole moment µ_e of hydrogen-bonded complexes formed by 4-amino-, 4-methylamino-, and 4-dimethylamino-N-methylphthalimides (4AMP, 4MAMP, and 4DMAMP) in proton-donor solvents. It has been established that µ_e = 11.68 D for 4AMP in alcohols, µ_e = 11.84 D for 4MAMP in alcohols, and µ_e = 13.19 D for 4DMAMP in alcohols and water.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 186–191, March–April, 2005.     

P2O5和H2SO4射流脱除单重态氧气流中的水汽

为提高化学氧碘激光的性能,用五氧化二磷(P2O5)和硫酸(H2SO4)射流进行了单重态氧气流中的水汽脱除实验。实验结果表明：在约4 kPa压力、20 m/s流速和5 ms停留时间的气流状态下,P2O5和H2SO4射流可将水汽含量分别降低至原来的约1/5和1/16,发烟硫酸甚至可降至约原来的1/90,而且对单重态氧的猝灭很小。P2O5和H2SO4都是极佳的常温射流除水剂。