CONCENTRATION AND SOLVENT SENSITIVE VISIBLE SPECTRA OF POLY(TRICYANOVINYLDIMETHYLANILINE): AGGREGATION AND SOLVATOCHROMISM

ABSTRACT

This work presents unusual spectral behavior of poly(tricyanovinyl dimethylaniline) (1) in dilute solutions. A new conjugated polymer(1) was prepared from p-(tricyanovinyl)N,N-dimethylaniline via the use of a methylglucopyranoside reagent. It is observed that dilute solutions of 1 exhibit spectral features associated with aggregation. The associative interaction is studied by changing the salt concentration of LiBr in DMF solution, by changing the concentration of 1, and by varying the solvents. The association modifies the visible spectrum of 1 in dilute solution. Spectra of 1 in DMF solution exhibit an intense absorption maximum at 429 nm, which can be assigned to the side group, with tailing past 700 nm. With increasing concentration, a new absorption band arises between 480 nm and 700 nm. LiBr dissociates the aggregate to decrease the additional spectral features. The visible spectrum of 1 varies in different solvents. The spectrum of 1 in chloroform solution exhibits two maxima at 490 nm and 550 nm. The associative interaction presumably arises from a dipole–dipole interaction among pendant side groups. In DMF solution of 1 in the presence of p-chloranil, the spectrum shows a maximum at 429 nm with a distinct shoulder near 520 nm which does not orginate from 1 and p-chloranil(CA) itself.     

二碘化铕的相变结构及荧光性质

本文用ＤＴＡ、Ｘ－ｒａｙ粉末衍射和荧光光度计等方法研究了ＥｕＩ２的相变和结构及荧光性质，用退火和淬火的方法得到了ＥｕＩ２的三种不同结构，并在荧光光谱上有不同的反映，首次发现ＥｕＩ２的低温变体，ＥｕＩ２－Ⅲ，正交晶系，空间群为ｐｎｍａ，ａ＝１．２２８７ｎｍ，ｂ＝０．４８８７ｎｍ，ｃ＝０．８３８４ｎｍ，Ｚ＝４。     

FLUORESCENCE AND THE LOCATION OF TRYPTOPHAN RESIDUES IN PROTEIN MOLECULES

Abstract— Fluorescence spectra of a number of native and denaturated proteins have been analysed, using spectral band width (ΔΛ), spectral maximum position (Λ_m), fluorescence quenching by external ionic quenchers, lifetime (b), and quantum yield ( q ) and its changes upon denaturation. The results enabled a model of fluorescence properties of tryptophan residues in the proteins to be substantiated by considering the existence of three discrete spectral classes, one buried in nonpolar regions of the protein (Λ_m 330–332 nm, ΔΛ= 48–49nm, q 0.11, τ= 2.1 ns) and two on the surface. One of the latter is completely exposed to water (Λ_m# 350–353 nm, ΔΛ= 59–61 nm, q # 0.2, τ= 5.4 ns); the other is in limited contact with water which is probably immobilized by bonding at the macromolecular surface (Λ_m# 340–342 nm, ΔΛ= 53–55 nm, q # 0.3, = 4.4 ns). Some quantitative predictions from the model, for (a) the fraction of fluorescence that is quenched by ionic quenchers, (b) the mean values of quantum yield, and (c) the mean values of fluorescence lifetime for various proteins, show good concordance with independent experimentally determined values.     

AUTOMATIC RECORDING OF ACTION SPECTRA OF PHOTOBIOLOGICAL PROCESSES, SPECTROPHOTOMETRIC ANALYSES, FLUORESCENCE MEASUREMENTS AND RECORDING OF THE FIRST DERIVATIVE OF THE ABSORPTION CURVE IN ONE SIMPLE UNIT

Abstract— A compact, rugged and simply constructed instrument has been designed which measures action spectra of photosynthesis by delivering equal numbers of quanta between 400 and 720 nm to a sample placed upon the cathode of an oxygen sensor. The absorption spectrum is measured delivering equal numbers of quanta over the spectrum to a sample placed directly above a photoreceiver that has been adjusted in wavelength sensitivity to function as a quantum counter. All the details that are recorded by conventional high precision spectro-photometers for samples with relatively broad absorption bands (e.g. chlorophyll, carotenoids, phycobilins and living material such as algal suspensions) are resolved by the instrument. Corrected excitation spectra of fluorescence are obtained with the same instrument. Likewise the first derivative of the absorption curve may be scanned. Such recordings amplify details in the absorption spectrum, and they are particularly useful in analyses of small changes in slope. The functions described above may be operated separately or combined. The instrument has a total weight of about 10 kg, and the dimensions are ca . 60 × 40 × 30 cm. It is constructed for use in field laboratories and on board research vessels, and also for courses in biology where the principles behind photobiological analyses are illustrated. It is possible that a device of this type could be used for investigations of photosynthesis on other planets.     

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.     

EXCITATION-ENERGY TRANSFER BETWEEN TYROSINE AND TRYPTOPHAN IN PROTEINS EVALUATED BY THE SIMULTANEOUS MEASUREMENT OF FLUORESCENCE AND ABSORBANCE

Abstract— The efficiencies of the excitation–energy transfer from tyrosine to tryptophan residues in eight globular proteins in the native and denatured states are obtained by studying the wavelength dependence of the fluorescence quantum yield. The measurements are made over a wide wavelength range using a computer-controlled spectrophotometer which can measure the fluorescence and absorbance simultaneously in one sample solution (Wada et al. , 1980). The values of the energy transfer efficiencies ranged from 0.17 ± 0.12 to 0.69 ± 0.06 in the native state and from -0.04 ± 0.09 to 0.12 ± 0.06 in the denatured state. These values are considerably lower than the values reported by Kronman and Holmes (1971); in particular, an almost complete absence of energy transfer for the denatured state is shown.     

EXCITATION ENERGY TRANSFER IN THE CRYPTOPHYTES. FLUORESCENCE EXCITATION SPECTRA AND PICOSECOND TIME-RESOLVED EMISSION SPECTRA OF INTACT ALGAE AT 77 K

Excitation spectra of chlorophyll- a (Chl- a ) fluorescence in intact cells of Cryptomonas ovata, Chroomonas pauciplastida and Chroomonas salina were determined at 77 K. For all species the excitation spectra for emission from Chl- a associated with photosystem II (PSII) showed increased contributions by a carotenoid (493 nm) and phycobiliproteins, and decreased contributions by carotenoid (417 nm, 505 nm) and Chl- a (445 nm) as compared to excitation spectra for emission from Chl- a associated with photosystem I (PSI). Excitation spectra of C. salina and C. ovata showed an increased contribution by Chl- c ² to PSII Chl- a fluorescence emission. In all three species the absorbance band positions of Chl- a , as determined from the excitation spectra, were similar to those previously described in green plants. green algae and phycobilisome-containing organisms. Time-resolved 77 K fluorescence emission spectra of C. ovata and C. salina showed successive emission from both phycoerythrin and Chl- c ², PSII Chl- a , and PSI Chl- a. C. pauciplastida showed successive emission from phycocyanin, PSII Chl- a , and PSI Chl- a. Spectral red-shifts with time were observed for the phycobiliprotein peaks in all three species. The fluorescence decay of phycoerythrin in C. ovata and C. salina was faster than that of phycocyanin in C. pauciplastida. The results are discussed in relation to the organization of the antenna pigments of PSII and PSI in the cryptophyte algae.     

ANION AND SOLVENT EFFECTS ON THE RATE OF REDUCTION OF TRIPLET EXCITED THIAZINE DYES BY FERROUS IONS

Abstract— The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl-sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.     

Ar+激光激励Pb2的色散荧光谱

The dispersed fluorescence spectra of Pb_2 dimer were recorded from the excitation of Ar~+ laser in HPOR. By the detailed spectroscopic analysis for this well-resolved fluorescence spectra, the ground state of pb_2 molecule and one of its electronically excited state were assigned preliminarily to be X~1∑_g~+ and F′Ⅱ_u state respectively.The spectral constants of the X and F are ω_e″=108.5 cm~(-1),ω_e″X_e″ = 0.209 cm~(-1), ω_e′=152.4 cm~(-1), ω_e′X_e′=0.636 cm~(-1) and T_e=19818,1 cm~(-1)., respectively     

对苯二甲酸酯类生色团与苯的激基复合物荧光光谱的溶剂效应

本文报道了对苯二甲酸酯类生色团与苯所形成的激基复合物并讨论了这类激基复合物的溶剂效应.结果表明,在这类激基复合物体系中,激基复合物谱带中发射峰的位置明显地受溶剂酸性的影响,在缺质子溶剂中,荧光峰红移较小,随着溶剂酸性的增强,激基复合物谱带的红移增大.激基复合物谱带中发射峰的位置与溶剂特性常数S之间的关系符合Brownstein公式.     

新型双发色团染料荧光光谱及其寿命的研究

有效的染料激光操作需要较高的荧光量子效率,若丹明是在500~700 nm光谱区中一类最重要的激光染料.然而,染料的基态分子和三线态对辐射能量的吸收将会大大降低激光输出效率,再者,由于若丹明类染料在紫外区的吸收系数较小,为了有效吸收泵浦能量(如用XeCI准分子激光,308 nm),就必须使用高浓度染料溶液,在这种情况下,若丹明类染料较小的Stokes位移就势必造成基态分子更大的重复吸收,即造成更大的谐振腔损耗^[1].     

THE EFFECT OF pH ON THE ABSORPTION AND FLUORESCENCE SPECTRA OF SANGUINARINE

Abstract— The influence of pH in the range 1.0 to 13.0 on the structure of sanguinarine has been investigated by spectrophotometric and spectrofluorimetric measurements. The data on absorption maxima, molar extinction coefficient, fluorescence emission maxima, relative fluorescence intensity and fluorescence quantum yield of the sanguinarine under various pH are presented. It is suggested that the pH dependent absorbance and fluorescence property of sanguinarine is due to the formation of the carbinolamine by hydroxylation at C-6 at alkaline pH.     

酸敏变色记录材料的光谱特性及其光量子产率

本文研究了由偏二氯乙烯-丙烯酸甲酯共聚合物(VdCl₂-MA)和五甲氧基红指示剂组成的酸敏变色记录材料的光谱特性,测定了其光分解量子产率.通过添加光敏剂使原来只有在254nm紫外光下曝光才能发生光分解反应的酸敏变色材料在35nm紫外光下曝光也可发生光分解而变色.酸敏变色材料在254nm处紫外光曝光量子产率为0.032-0.020;在35nm处紫外光曝光量子产率为0.110-0.034.光敏剂的加入使酸敏变色材料量子产率提高了2-4倍.     

LUMINESCENCE SPECTRA AND PHOTOCYCLOADDITION OF THE EXCITED COUMARINS TO DNA BASES

Abstract— The lowest excited singlet and triplet states of coumarin, psoralen, and 4-hydroxy-coumarin have been assigned to the (π,π * ) type on the basis of the luminescence spectroscopy and MO calculations. The mechanism of photocycloaddition of courmarin and psoralen to thymine has been described in terms of the perturbational MO model and MO reactivity indices. All possible cycloaddition patterns have been examined. Results suggest that the 3,4-bond of coumarin in the excited state is somewhat more reactive than the same bond of psoralen in the excited state. It is also predicted that the 3,4-bond of psoralen in the triplet state is more reactive than the 4', 5'-bond. The results have been favorably correlated with the electronic characteristics of excited coumarin molecules and with available experimental data on the relative yields of photoadducts.     

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.     

ACIDITY DEPENDENCE OF THE ABSORPTION AND FLUORESCENCE SPECTRA OF ISOFLAVONE AND 7-HYDROXYISOFLAVONE

-The pH and H₀ dependence of the absorption and fluorescence spectra of isoflavone and 7-hydroxyisoflavone are reported. Isoflavone is fluorescent in acidic solution only, whereas 7-hydroxyisoflavone is fluorescent in all acidity ranges under investigation. Ground and first excited singlet state p K _a's have been determined spectrophotometrically and fluorimetrically, respectively. Excited state protolytic equilibration processes via a second order reaction (proton gain) are found to be too slow to compete efficiently with fluorescence. This is deduced from the close agreement between the p K _a's of the conjugate acids obtained by absorption and fluorescence titrations. On the other hand, photodissociation of 7-hydroxyisoflavone proceeds faster than its fluorescence decays. The experimental p K _a(S₁) is in fair agreement with the calculated one. 7-Hydroxyisofiavone forms a phototautomer (or exciplex) in the pH 2 to H₀-1 acidity range, which is characterized by its long wavelength emission. Quantum efficiencies are given for isoflavone and 7-hydroxyisoflavone in aqueous solutions of various acidities. Deuteration effects thereon are discussed.     

STUDIES ON ENERGY DISSIPATION IN PHYCOBILISOMES USING THE KENNARD-STEPANOV RELATION BETWEEN ABSORPTION AND FLUORESCENCE EMISSION SPECTRA

Absorption and fluorescence emission spectra were measured at room temperature ( ca. 22°C) for solutions of phycocyanin-1, phycocyanin-2 and allophycocyanin from Phormidium luridum , and also for phycobilisome preparations from various blue-green algae ( Anabaena variabilis, Nostoc muscorum strain A, Nostoc sp. strain Mac, Phormidium luridum ). Kennard-Stepanov (KS) temperatures ( T ) were computed using the Kennard-Stepanov relationship F () = b A () ^-5 exp(-h/ kT ), where F () stands for fluorescence (energy per wavelength interval) as a function of wavelength (), A () is absorbance as a function of wavelength, b a proportionality factor, and h, c and k are Planck's constant, the velocity of light and Boltzmann's constant, respectively.
In most cases experimenta/ data followed the expected relationship, but at low ionic strength allophycocyanin gave a clearly biphasic KS plot, i.e. In ⁵ F ()/ A () vs 1/. This could be due to the presence of both monomers and trimers in the sample at low ionic strength.
For purified allophycocyanin and phycocyanins (PC-1 and PC-2) as well as phycobilisomes from Phormidium luridum , the KS temperatures were only slightly (insignificantly) elevated above the sample temperature. Thus, after absorption of a photon, vibrational and configurational equilibration is essentially completed before emission of the fluorescence photon takes place.
For phycobilisomes from Anabaena variabilis and the two Nostoc species the KS temperatures were moderately elevated. Since there was no correlation between radiation temperature and excitation wavelength, the elevation is not due to excess (undissipated) vibrational energy, but rather to incomplete configurational equilibration.     

SOLVENT EFFECTS ON THE ELECTRONIC ABSORPTION AND FLUORESCENCE SPECTRA OF INDOLE-4-CARBOXYLIC ACID: PROTOTROPIC EQUILIBRIA IN AQUEOUS SOLUTIONS

Abstract— The absorption and fluorescence spectra of indole-4-carboxylic acid in various solvents have indicated that the -COOH group is more planar with respect to the indole ring in the first excited singlet state (S₁) than in the ground (S₀) state. Relatively large Stokes' shifts indicate that polarisability and dipole moment of the molecule are increased predominantly upon excitation. Prototropic reactions in the S₀ and S₁ states are the same. The -COO^- and -COOH+₂ groups are not coplanar in the S₀, but coplanar in the S₁ state. pH-dependent fluorescence spectra have revealed that both protonation and deprotonation of the -COOH group increase the basicity of the molecule upon excitation.     

DIRECT DETECTION OF SINGLET OXYGEN SENSITIZED BY HAEMATOPORPHYRIN AND RELATED COMPOUNDS

Abstract— Direct time-resolved detection of the luminescence at 1270 nm from 'singlet oxygen' was used to estimate the quantum yield of singlet oxygen production (Φ_Δ) from a series of related porphyrins in benzene and in D₂O. From this and available data the fraction of oxygen quenching interactions leading to singlet oxygen production (S_Δ) was derived in most cases. A marked increase in Φ_Δ value was observed for di-haematoporphyrin ester (DHE) in cetyltrimethyl ammonium bromide/D₂O solution in comparison to D₂O alone, this increase is attributed to a major structural alteration of DHE on introduction of the detergent.     

THE FLUORESCENCE OF ADENINE. THE EFFECTS OF SOLVENT AND TEMPERATURE ON THE QUANTUM YIELD

Abstract— To investigate the mechanism of the solvent and thermal quenching of fluorescence, the absolute fluorescence quantum yield of adenine has been determined in several alcoholic glasses as a function of the concentration (10^-5-10^-4M) and temperature (77°-298°K). The yield is independent of the concentration but increases with decreasing temperature and increasing bulk cohesion and rigidity of the solvent.
The environmental effects on the yield are attributed to radiationless electronic relaxation processes caused by solute-solvent interaction. Increasing the temperature and decreasing the intra-solvent cohesion cause increases in the interaction and therefore accelerate the relaxation. The rate determining step behaves like a diffusion in the limit of low viscosity.