准一维有机电荷迁移晶体电导率和温度的关系

在有机电荷迁移晶体中,有一类是由荷正电的施体分子柱与荷负电的受体分子柱交错平行排列而成,如TTF-TCNQ,因为这类晶体具有很强的各向异性,表现为准一维导体.实验得到,在T_P相似文献   

THE TEMPERATURE DEPENDENCE OF PHYTOCHROME TRANSFORMATIONS

Abstract— The kinetics of phytochrome transformation were examined over a 30°C temperature range (+5° to–25°C) in 75% glycerol. Two new intermediate reaction stages are described for the transformation of the red-absorbing form, P _r to the far-red absorbing form, P _fr The free energies, enthalpies and entropies of activation were obtained for five of the six reaction stages observed in the transformation of P _r to P _fr and for the two reaction stages observed in the reverse process. All exhibited positive entropies of activation with the maximum being 25 entropy units. The results suggest that the phototransformations between P _r and P _fr consist of relaxation processes beginning with the intermediate produced immediately upon absorption of a quantum of light and ending with either P _r or P _fr.     

DEPENDENCE OF INTERSYSTEM CROSSING ON EXCITATION ENERGY IN OROTIC ACID

Abstract— Photochemical dimerization in orotic acid in aqueous solution has been studied as a function of oxygen concentration, orotic acid concentration and the wavelength of irradiation under two pH conditions. One dimer was detected. Analysis of the data enabled us to obtain a minimum estimate of the efficiency of intersystem crossing, ø_ISC. from singlet to triplet levels. This efficiency increases by a factor of two with increasing energy of excitation over the wavelength range 240–302 nm, and by a similar factor between pH 3 and pH 1. The maximum value obtained was 0.15 for irradiation at 240 nm at pH 1. The relation between quantum yield and ø_ISC is discussed and possible mechanisms to explain this variation of ø_ISC with energy are proposed.     

EXCITATION ENERGY TRANSFER IN SYSTEMS OF MANY MOLECULES

Abstract— Förster's theory of energy transfer in condensed systems is re-examined in the light of recent criticisms. It is concluded that his approach is correct and holds for a wide range of donor and quencher concentrations as long as there is no transfer among donor molecules. In contrast, the modified result of Tweet, Bellamy and Gaines, holds only for complete delocalization of the excitation among the donor molecules.     

聚对苯二甲酸乙二酯荧光光谱的激发波长依赖性研究

聚对苯二甲酸乙二酯（PET）的荧光光谱已经得到了相当广泛和深入的研究,当激发光波长位于310～360nm时,可以观察到位于360～390nm范围的荧光发光,这部分荧光的来源有很多争议,至今未取得一致的看法,有作者认为,此处的荧光发光是PET链段上苯环之间的相互作用形成的基态二聚体（ground-state dimer）引起的发光;还有人认为这是苯环基团之间相互作用形成的激基缔合物的发光（excimeric emission）。     

INVESTIGATION OF MIGRATION PARAMETERS OF ELECTRON EXCITATION ENERGY IN PHOTOSYNTHETIC and ARTIFICIAL SYSTEMS

Abstract— The technique for the determination of diffusion parameters on the basis of nonlinear fluorescence quenching and excitation energy capturing by the traps is discussed. The nonstationary character of the processes of excitation capturing by traps and of singlet-singlet annihilation which occur upon the system excitation by a picosecond pulse is taken into account. The obtained values of the diffusion parameters in the artificial pigment-polymer antenna system (the diffusion coefficient ∼ 10^-2 cm² s^-1 and the diffusion length ∼ 500 Å) are close to those in the photosynthesizing systems. It is also shown that the method of the determination of diffusion parameters on the basis of excitation capturing by the reaction centres may be applied for the study of the native photosynthetic systems.     

TRANSFER OF EXCITATION ENERGY BETWEEN PORPHYRIN CENTERS OF A COVALENTLY-LINKED DIMER*

Abstract— Three covalently-linked porphyrin hybrid dimers were synthesized, each containing a metallotetraarylporphyrin [Zn(II), Cu(II), or Ni(II)], and a free base tetraarylporphyrin. Transfer of singlet excitation energy from the metalloporphyrin center to the free base porphyrin center was determined by measuring fluorescence properties. The Zn hybrid dimer displayed excellent intramolecular transfer of energy ( 85%) from the excited singlet state of the Zn(II) chromophore to the free base chromophore. No evidence for such transfer of the excited singlet state energy was found in the Ni(II) or Cu(II) analogues. From our experimental data, the fluorescence quantum yield of the Zn hybrid dimer was the same as for the free base monomer porphyrin (0.11; Seybold and Gouterman, 1969). Thus, the covalent attachment of another fluorescent porphyrin center effectively doubled the antenna size without decreasing the quantum yield even though the fluorescence quantum yield of the Zn(II) containing monomer was substantially less (0.03, according to Seybold and Gouterman, 1969) than that of the free base porphyrin. The donor-acceptor distance and the rate constant for energy transfer were calculated using the Forster equation. Assuming random orientation, a donor-acceptor distance of 15 Å was calculated with an associated rate constant (k_ci) for energy transfer of 1.9 ± 10₉ s_–1.     

EXCITATION ENERGY TRANSFER IN BILIRUBIN-CHLOROPHYLL AGGREGATES

Abstract— Solutions of chlorophyll a (chl a ) with different concentrations of bilirubin (blr) were used as a model system for studying the mechanism of energy transfer between bili-proteins and chl in blue-green algae. Several optical properties such as the absorption spectra, emission spectra for different wavelengths of excitation, degree of polarization and lifetime of fluorescence were measured. The measurements were carried out in several solvents (of different hydrogen bond-forming capacities) and at various dye concentrations.
The results indicate that aggregates of chl with blr are formed. Energy absorbed by blr in the aggregates is emitted as chlorophyll fluorescence, indicating energy transfer from blr to chl within the aggregate. The fluorescence yield and fluorescence polarization of aggregates are lower than those of isolated chl.     

聚二甲基硅氧烷甲苯溶液特性粘数的温度依赖性

按照Flory-Fox的稀溶液理论,一个线型高分子在θ-溶剂中的特性粘数和它的分子量有下列关系:     

合成高分子膜透气速率的温度依赖性

近年来以气体选择性分离为目的的合成高分子膜的研究取得了巨大的进步。气体分离膜的两个基本性能参数是透气速率J及选择系数α。同一个膜,在较高温度使用时,往往是J值增大,α值下降,因此选择适当地操作温度,以便得到最佳的J-α搭配是很重要的。本文讨论了甲基硅橡胶(MSR)、天然橡胶(NR)、乙丙橡胶(EPR)、聚乙烯(PE)、聚(4-甲基戊烯-1)(TPX)等材料的均质膜或复合膜,在不同温度下的氧、氮透过速率,计算了各种膜材料的氧、氮表观透过活化能,并对其本质进行了探讨。     

PHOTOCHEMISTRY OF TYPE I ACID-SOLUBLE CALF SKIN COLLAGEN: DEPENDENCE ON EXCITATION WAVELENGTH

Although previous studies have demonstrated that the predominant photochemistry of type I collagen under 254 nm irradiation may be attributed either to direct absorption by tyrosine/phenylalanine or to peptide bonds, direct collagen photochemistry via solar UV wavelengths is much more likely to involve several age- and tissue-related photolabile collagen fluorophores that absorb in the latter region. In this study, we compare and contrast results obtained from irradiation of a commercial preparation of acid-soluble calf skin type I collagen in solution with UVC (primarily 254 nm), UVA (335–400nm) and broad-band solar-simulating radiation (SSR; 290^1–00nm). Excitation spectroscopy and analysis of photochemically induced disappearance of fluorescence (fluorescence fading) indicates that this preparation has at least four photolabile fluorescent chromophores. In addition to tyrosine and L-3,4-dihydroxyphenylalanine, our sample contains two other fluorophores. Chromophore I, with emission maximum at 360 nm, appears to be derived from interacting aromatic moieties in close mutual proximity. Chromophore II, with broad emission at430–435 nm, may be composed of one or more age-related molecules. Collagen fluorescence fading kinetics are sensitive to excitation wavelength and to conformation. Under UVC, chromophore I fluorescence disappears with second-order kinetics, indicating a reaction between two proximal like molecules. Adherence to second-order kinetics is abrogated by prior denaturation of the collagen sample. A new broad, weak fluorescence band at400–420 nm, attributable to dityrosine, forms under UVC, but not under solar radiation. This band is photolabile to UVA and UVB wavelengths. Amino acid analysis indicates significant destruction of aromatic amino acids under UVC, but not under UVA or SSR. When properly understood, collagen fluorescence fading phenomena may act as a sensitive molecular probe of structure, conformation and reactivity.     

INFLUENCE OF THE ENVIRONMENT ON THE EXCITATION WAVELENGTH DEPENDENCE OF THE FLUORESCENCE QUANTUM YIELD OF INDOLE

Abstract— The influence of excitation wavelength, pH, oxygen and solvents, upon fluorescence quantum yields, were measured for insole Indole in neutral aqueous solution exhibits the same wavelength dependence as tryptophan, which indicates that COO- absorption is not responsible for the effect. Parameters such as pH and oxygen influence only the absolute fluorescence quantum yields but not their relative variation with wavelength, indicating competition with fluorescence emission for S1 deactivation. without any influence upon deactivation of higher excited states. In contrast, solvents exhibit a specific influence upon the wavelength dependence; for indole, the decrease of fluorescence yield excited around 215 nm, compared with the yield in the first absorption band is about 40% in water, 10% in acetonitrile, 70% in n-hexane and cyclohexane, whereas no appreciable decrease occurs in methanol, ethanol or n-butanol. These observations, together with the Stokes shifts of the emission spectra, may be well correlated with Kosower's Z-values, expressing microscopic solvent-solute interactions.     

THE MECHANISM OF SINGLET-SINGLET EXCITATION ENERGY TRANSFER FROM CAROTENOIDS TO CHLOROPHYLL

Abstract— It is proposed that the light-harvesting function of carotenoids in photosynthesis requires electron exchange between the energy donor (carotenoids) and the acceptor (antenna Chi molecules); this supports an earlier suggestion by Goedheer (1972) that there exists a close spatial relationship between these pigments in vivo.     

TEMPERATURE DEPENDENCE OF PHOTOSENSITIZED ELECTRON TRANSPORT ACROSS LIPID VESICLE WALLS

Abstract— An overall Arrhenius activation energy of 117 plusmn; 19 kJ/mol (28.0 plusmn; 4.5 kcal/mol) has been measured for photosensitized electron transport across phospholipid vesicle walls in the temperature range 18–38°C. A dynamic model for the overall process is proposed which accounts for the parabolic growth curves of the kinetically probed species, heptyl viologen radical. The temperature dependence of the initial quantum yield derived from these curves, and of fluorescence quenching behavior of the ruthenium tris-bipyridyl photosensitizer, is used to estimate an activation energy of 67 plusmn; 21 kJ/mol(16 plusmn; 5 kcal/mol) for the electron transport step itself. The activation energy for the co-transport of charge compensating ions is estimated to contribute no more than 4.6 kJ/mol to this energy.     

COHERENT MOTION AND TRANSFER OF EXCITATION ENERGY IN THE PRIMARY PROCESSES OF PHOTOSYNTHESIS

Fluorescence decay curves are calculated within the framework of the Liouville von Neumann equation for simple model systems of a photosynthetic unit consisting of a reaction center coupled to either a linear chain or a hexagonal array of identical antenna pigments. A comparison of the results with those obtained by solving the Pauli Master equations reveals that in the case of coherent excitation energy transfer the fluorescence decay kinetics exhibit a strong dependence on the topological array of the antenna pigments. For systems with a different pigment array, markedly different kinetics can be expected upon decreasing the pure dephasing time.     

聚N—异丙基丙烯酰胺溶液的温度依赖关系

用自由基聚合法合成了聚Ｎ－异丙基丙烯酰胺（ＰＮＩＰＡＡＭ）样品，用乌氏粘度计考查了该聚合物的四氢呋喃（ＴＨＦ）溶液和水溶液的粘度与温度的依赖关系。发现ＰＮＩＰＡＡＭ－ＴＨＦ体系的特性粘数随温度升高而增大，ＰＮＩＰＡＡＭ－Ｈ２Ｏ体系的特性粘数－温度曲线表现出较为复杂的变化规律。并用实验确定的特性粘数对合成样品的分子量进行了表征Ｍｎ＝８．４４×１０＾５ｇ·ｍｏｌ＾－１。     

THE TEMPERATURE DEPENDENCE OF Pfr ACTION GOVERNS THE UPPER TEMPERATURE LIMIT FOR GERMINATION IN LETTUCE

In most cultivars of lettuce (Lactuca saliva L,), red light acting through the red/far-red reversible phytochrome system promotes full germination within the20–30°C range, but at progressively higher temperatures germination declines sharply. The relationship between this upper ternperature limit for germination and the temperature dependence of phytochrome action was investigated in Grand Rapids lettuce. In fresh seeds the GT₅₀ (temperature giving half maximal germination) was ca 29–30°C. In these seeds, escape from far-red reversibility did not occur at 35°C, a temperature above the GT₅₀, but occurred rapidly at 27°C, a temperature below the upper limit. Increasing periods of dark pretreatment at high temperature (35°C) or increasing concentrations of the germination inhibitor coumarin caused a progressive decline in the GT₅₀, Escape from photoreversibility did not occur at 27°C in seeds in which the GT₅₀ had been reduced to less than 25°C by coumarin or by prolonged high temperature pretreatment. These results indicate that there is a close correlation between the position of the upper temperature limit for germination, and the temperature dependence of phytochrome action. We conclude that factors that alter the upper temperature limit for germination do so by changing the temperature dependence of phytochrome action.     

EXCITATION WAVELENGTH DEPENDENCE OF PROTOTROPIC DISSOCIATION AND TAUTOMERISM OF SALICYLAMIDE IN THE LOWEST EXCITED SINGLET STATE

Abstract—The fluorescence spectra of salicylamide in cyclohexane, ethanol and at different pH in water were studied. The short and long wavelength fluorescences observed in the organic solvents originate from emissions of a weakly or non-intramolecularly hydrogen bonded conformer and from phototautomerization of a strongly intramolecularly hydrogen bonded conformer, respectively. Evidence for at least 2 conformers in the ground state exists in the excitation wavelength dependence of the ratio of short wavelength to long wavelength emission. In water, prototropic dissociation of the phenolic group of salicylamide in the lowest excited singlet state also shows an excitation wavelength dependence, indicating that the weakly or non-intramolecularly hydrogen bonded conformer in water is predominately responsible for photodissociation.