MECHANISM OF PHOTOREDUCTION OF THIAZINE DYES BY EDTA STUDIED BY FLASH PHOTOLYSIS-II. pH DEPENDENCE OF ELECTRON ABSTRACTION RATE CONSTANT OF THE DYES IN THEIR TRIPLET STATE

Abstract— The pH dependence of the apparent reactivity of thiazine dyes in their triplet states has been studied in aqueous solutions, using as electron donor HY^-3, the trianionic species of ethylene diamine tetraacetic acid (EDTA), in the pH range 4–8. The pH dependence is found to be related to a change in the degree of protonation of the triplet excited dye. The apparent reactivity and lifetime of two differently protonated forms of thionine, azur B and methylene blue were determined by classical and dye-laser flash techniques, making it possible to evaluate the rate constant for electron abstraction of these molecules in their triplet states. It is found that: (a) protonation on the ring nitrogen increases the electron-abstraction rate constant of the triplet-state species about twenty-fold, and (b) methylation on the side amino groups decreases it.     

SOLVENT AND TEMPERATURE EFFECTS ON THE EXCITED SINGLET STATE ABSORPTION OF DIPHENYLBUTADIENE

Nanosecond excited state absorption spectra of all-trans-1,4-diphenyl-1,3-butadiene (DPB) and a rigid s-cis DPB analog, 1,4-diphenyl-1,3-cyclopentadiene, were obtained in several hydrocarbon solvents at room temperature and low temperatures. Analysis of the excited state absorption spectra of these two molecules suggests the presence of excited state s-cis rotamers in DPB at room temperature.     

配位体 SO_4~(2-)对激发态铀(Ⅵ)去活化的影响

近年来,随着激光、微弱信号测量以及瞬态测量技术等发展,对溶液中激发态离子的化学和物理行为的研究已日益受到人们的重视,激发态铀酰离子发光衰减的研究尤为活跃.Marcantonatos 等、Formosinho 等以及郑企克、王志麟等对高氯酸溶液中激发态铀酰离子的发光衰减过程进行了详细的研究.探讨了ClO_4~-溶液中pH 等对激发态铀酰离子的发光衰减的影响,观察到了一定的pH 条件下激发态铀(Ⅵ)的非单一指数衰减,并各自提出了不同的解释.值得提出的是,上述的一系列研究都是在高氯酸溶液中,其它体系中铀(Ⅵ)的发光哀减的研究进行得很少,报导则更少.1983年Joshi 等曾研究了80K 时SO_4~(2-)     

MECHANISM OF PHOTOREDUCTION OF THIAZINE DYES BY EDTA STUDIED BY FLASH-PHOTOLYSIS-I

Abstract— The photoreduction of thiazine dyes by ethylene diamine tetraacetic acid (EDTA) was investigated by Rash photolysis. This reaction was found to occur according to a three-step mechanism. the first being the formation of the dye triplet state followed, in weakly acid solutions, by protonation. During the second step, the triplet state of the dye disappears through two competing processes: spontaneous deactivation and reaction with EDTA, which leads to the semireduced dye. The third step leads to the leucodye. It is shown that the overall quantum yield of photoreduction is governed by the second step and can be calculated from the ratio of the rate constants of the two elementary processes involved in this step. This ratio was measured over a wide pH range.     

QUANTIFICATION OF THE SOLVENT EFFECTS ON THE TRIPLET QUANTUM YIELD OF PSORALEN BY THE "LINEAR SOLVATION ENERGY RELATIONSHIP"

Triplet formation quantum yields (Φ_τ) of psoralen in a set of 17 pure solvents ranging from n -hexane to water and in dioxane: water mixtures were obtained by nanosecond laser flash photolysis. The triplet yield increases with solvent polarity. The extremum values are 0.009 and 0.545 in n -hexane and water, respectively. Good correlations of the experimental Φ_τ values with empirical "polarity" scales (Dimroth/Reichardt's E_T [30], Kamlet/Taft's solva-tochromic parameters β, and α, and Swains acity/basity A_S/B_S) were obtained: Ln(φ_T^-1 - 1) = 8.86 - 0.143E_T(30) Ln(φ_T^-1 - 1) = 4.40 - 2.34_τ - 1.70α Ln(φ_T^-1 - 1) = 4.65 - 3.72A_s - 1.12B_s The results are discussed in terms of the sensitivity of psoralen triplet quantum yield to solvent polarity and hydrogen-bonding abilities.     

PHOTOCHEMICAL INVESTIGATIONS OF OXAZINE, THIAZINE AND SELENAZINE DYES. THE REACTIVITY OF PROTOLYTIC TRIPLET FORMS IN ELECTRON TRANSFER REACTIONS

Abstract— The photoreduction of oxonine, thionine and selenine with the reducing agent allylthiourea was investigated by flash photolysis. The oxonine triplet state was produced by triplet-triplet energy transfer with 9,10-dibromoanthracene as donor. For all three dyes the rate constant of the electron transfer is considerably higher for the acid triplet form than that of the corresponding reaction of the basic triplet form. It is shown that the higher reactivity of the acid triplet can be related to its higher reduction potential which is available from the difference of the pK values of triplet and semiquinone of the dye.     

新型吡喃鎓方酸菁染料溶剂效应、聚集行为研究

本文研究了五个吡喃鎓方酸菁染料的溶剂效应,发现最大吸收峰波数υ与函数f(n,ε)存在较好的线性关系,而Bayliss函数项(n²-1)/(2n²+1)决定了吸收光谱的位移变化Δυ,同时还分析了氢键相互作用对理论函数模型的误差.根据染料的聚集动力学证实了染料在正丙醇/水(4:21,体积比)体系中确有二聚体的产生,并发现了两组不同的聚集特性.此外,使用APCIMS质谱技术证实Dye3二氯甲烷浓溶液中也产生了二聚体.     

取向对物理老化的聚对苯二甲酸乙二酯纤维溶剂诱导结晶速率的影响

通过密度法、ＤＳＣ、力学性能测试等方法研究了物理老化对聚对苯二甲酸乙二酯（ＰＥＴ）纤维溶剂诱导结晶速率及结构的影响，并进一步探讨了取向程度对ＰＥＴ纤维物理老化过程的影响．发现在一定老化温度下，ＰＥＴ纤维的溶剂诱导结晶（ＳＩＮＣ）速率随老化时间的延长呈现先降低后升高的趋势；取向程度高的样品则经较短的老化时间即可出现这种情况．对上述现象用凝聚缠结的观点加以解释．     

STUDIES ON THE TRIPLET EXCITED STATE OF 4-THIOURIDINE

Abstract— The absorption spectra, lifetimes, extinction coefficients and intersystem crossing quantum yields of the lowest triplet T ₁ of 4-thiouridine have been determined both in acetonitrile and in water. An ordering of ^1,3(n,π)* and ^1,3(π,π)* states is suggested. Triplet quenching rate constants with various pyrimidine bases or amino acids are reported.     

螯合萃取和协同萃取的溶剂效应

本文测定了1-苯基-3-甲基-4-苯甲酰基吡唑啉酮-5(HPZL)-Zn²⁺萃取体系在不同溶剂中的萃取平衡常数以及其他几个协萃体系的协萃平衡常数,结果列于表4～8.证实惰性溶剂对萃取平衡常数的影响可以近似地用正规溶液理论解释,非惰性溶剂的影响则和它们的配位作用有关.对于协萃体系,协萃平衡常数β_n0k⁰随溶剂不同有很大变化,其中中性协萃剂活度系数的变化起重要作用.     

照相染料还原电位的研究

本文测定了八个照相染料在不同pH条件下的还原电位。发现其中一些增感染料的还原电位与其溶液的pH值无关,而一些减感染料依赖于pH值的变化。本文用染料质子化机理分析了这些结果。     

THE TRIPLET EXCITED STATES OF BILIVERDIN AND BILIVERDIN DIMETHYL ESTER

Abstract— The triplet states of biliverdin and biliverdin dimethyl ester have been generated using pulse radiolysis excitation. Biliverdin triplet was formed by energy transfer from biphenyl triplet in acetone, absorbed throughout the wavelength range studied (380–1000 nm) and had a half-life of 11.7μs under the cpnditions chosen. Biliverdin dimethyl ester triplet was formed by energy transfer from biphenyl triplet in benzene, likewise absorbed throughout the wavelength range studied (360–1000 nm) and had a half-life of 6.7μs under the conditions used. Both biliverdin and biliverdin dimethyl ester efficiently quench anthracene, naphthacene, but not μ-carotene, triplet states. On the other hand. neither μ-carotene nor oxygen were found to quench the triplet states of biliverdin or biliverdin dimethyl ester. Estimates or limits for the rate constants of all these quenching reactions were obtained. These reactivities suggest that the triplet levels of both biliverdin and biliverdin dimethyl ester lie around 90 kJ mol^-1. The triplet energy transfer rate from bilirubin to biliverdin dimethyl ester in benzene was measured to be 1.9 × 10⁹ M^-1 s^-1. The singlet-triplet intersystem crossing efficiencies of both molecules were very low, limits of 0.004 and 0.001 being found for biliverdin and biliverdin dimethyl ester, respectively, using 347 nm laser excitation.     

QUENCHING OF THE EXCITED STATES OF 2-PHENYLBENZOXAZOLE BY AZIDE ANION. FLUORESCENCE AND ESR STUDY

Electron spin resonance, spin-trapping and fluorescence techniques demonstrate that 2-phenylbenzoxazole (P) participates in photo-induced reactions with alcohols and electron donors like the azide ion. Irradiation of Pat 300 nm in deaerated ethanol produces ethoxyl and hydroxyethyl radicals which can be detected with the spin trap, 5,5-dimethyl-l-pyrroline-l-oxide (DMPO). However, irradiation of P in the presence of N^-₃ leads to the appearance of the azide radical, N^-₃, which also reacts with DMPO. Studies with the nitroxyl radical, 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO), suggest that electron transfer from the azide anion to an excited state of P yields the semi-reduced sensitizer, P^-, which in turn reacts with TEMPO. The effect of sodium azide upon the fluorescence intensity and lifetime of P in aqueous ethanol has also been studied.     

粒径和流速对吸附速率的影响

本文主要考察了吸附剂的粒径大小及动态循环时流速大小对吸附速率的影响，根据膜扩散限制和孔隙扩散限制的理论模型对其影响作了定量描述。     

THE QUENCHING OF EXCITED STATES OF HYPOCRELLIN A BY RARE EARTH IONS

The quenching processes of prompt and delayed fluorescence of hypocrellin A by rareearth ions were investigated. It is demonstrated that the prompt fluorescence of HA can bequenched efficiently by RE in methanol via a static quenching process including a groundstate complex formation. The thermally induced delayed fluorescence of HA can also bequenched effectively by complex formed, which quenching is of dynamic quenching behavior.The fluorescence quenching of HA in various micellar systems which protect the quenchingby the compartmentalization of micelles is discussed as well.     

TRIPLET EXCITED STATES OF PYRIMIDINE NUCLEOSIDES AND NUCLEOTIDES

Abstract— The triplet absorption spectra, lifetimes, extinction coefficients, e_TT, and intersystem crossing quantum yields to the lowest triplet T₁, ø_T1, of thymidine, thymidine monophosphate, uridine and uridine monophosphate, have been determined in various solvents at 300 K.
The effect of H-bonding on ø_T1, of these nucleosides and nucleotides and also of uracil has been determined and discussed. This effect allows, an ordering of ^l,3 n, π* and ^1,3 π, π* states in protic and aprotic solvents.     

DECAY KINETICS OF THE TRIPLET EXCITED STATE OF LUMIFLAVIN

Abstract— The rate of decay of the triplet state of lumiflavin in deaerated phosphate buffer at pH 6.9, has been studied using the flash photolysis technique, at various concentrations and flash energies. The decay of the transient appears as a mixture of first and second order processes, the relative importance of which depends on the experimental conditions.
The following competitive reactions have been found to explain the course of the reaction of the triplet excited state of lumiflavin.     

ACID-BASE EQUILIBRIA OF THE EXCITED SINGLET AND TRIPLET STATES AND THE SEMI-REDUCED FORM OF ACRIDINE ORANGE

Abstract— The acid-base equilibria of the excited singlet and triplet states of acridine orange (AO) were studied by flash-photolysis and fluorometric methods. The dye is a stronger base in the first excited singlet state (pK_s= 13.3) than in the triplet and ground states (pK_r= 10.3: pK_c, = 10.2); acridine orange follows the trend observed with some other heterocyclic compounds, viz. pK_s > pK_r= pK,_c. At room temperature, an anomalous fluorescence occurs from the dye in basic media: the assignment of this emission is discussed.
The semi-reduced dye was studied as a function of pH. In a large pH range (3–14), only the protolytic equilibrium between the cationic (AOH₂⁺) and the neutral (AOH) radicals was observed; the pK value corresponding to this equilibrium was found to be in the range of pH 5–6.