ROOM-TEMPERATURE STEADY-STATE FLUORESCENCE PROPERTIES OF POLY(dG-dC).SPOLY(dG-dC)

We report the steady-state fluorescence properties of the alternating polynucleotide poly(dG-dC).poly(dG-dC) in low-salt solution at room temperature for excitation at the Hg lines 265, 280 and 297 nm. Its fluorescence spectrum peaks at about 325 nm and, within the experimental error, its shape does not change significantly with the excitation wavelength. The fluorescence anisotropy is found to decrease strongly for short-wavelength excitation, a behavior which is very similar to that exhibited by free guanine. In view of the fact that the anisotropy for free cytosine is virtually constant at the aforementioned three excitation wavelengths, the results suggest that in this polynucleotide the emission stems from guanine. The values of the fluorescence quantum yield for the three excitation wavelengths are found to be very low, 0.8 x 10(-5), 0.8 x 10(-5), and 2.8 x 10(-5), respectively; these are compatible with transfer of energy from the lower-energy electronic state of guanine, before vibronic relaxation is established, to cytosine. Upon denaturation, the fluorescence spectrum becomes very broad and the fluorescence quantum yield increases; these observations support the authenticity of the emission from the nondenatured polynucleotide.     

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）。     

ROOM-TEMPERATURE FLUORESCENCE PROPERTIES OF THE POLYNUCLEOTIDE POLYdA POLYdT

The room-temperature fluorescence spectrum of the non-alternating polynucleotide polydA.polydT is found to have its maximum at about 325 nm and, when exciting in the spectral region where both adenine (A) and thymine (T) absorb, to coincide with that obtained for excitation at 293 nm where thymine is selectively excited. The fluorescence anisotropy is found to be equal to 0.18 and independent of the excitation and emission wavelengths. These observations are consistent with: (i) emission stemming from T; and (ii) transfer of electronic energy from A to T being not efficient. These inferences are also supported by the observed dependence of the fluorescence quantum yield on the excitation wavelength.     

A PORPHYRIN-DNA EXCIPLEX: RESONANCE RAMAN SPECTRA OF ELECTRONICALLY EXCITED Cu(TMpy-P4) BOUND TO POLY(dA-dT)-POLY(dA-dT)

The resonance Raman spectra of water-soluble porphyrins, Cu(TMpy-P4) and Ni(TMpy-P4), and their mixtures with DNA, Poly(dG-dC).Poly(dG-dC), and Poly(dA-dT).Poly(dA-dT) were measured using 426 nm pulsed laser excitation (and 556 nm for some applications). At high laser power, the solution of Cu(TMpy-P4) mixed with DNA or Poly(dA-dT).Poly(dA-dT) exhibits new bands at 1550 and 1349 cm-1 that are not observed for Cu(TMpy-P4) alone or for Cu(TMpy-P4) mixed with Poly(dG-dC).Poly(dG-dC). These extra bands do not appear when the resonance Raman spectra are measured by a cw laser or by a pulsed laser with low power. Similar mixtures of M(TMpy-P4) (where M = Ni, Zn, Co, Mn, and H2) with these nucleic acids exhibit no such bands even by high power pulsed laser excitation. We attribute the new resonance Raman bands to an electronically excited Cu(TMpy-P4), stabilized by forming an exciplex with the A-T site of the nucleic acid. The minimum lifetime value of such an exciplex was estimated to be on the order of 10 ps.     

Parametric investigation of laser-induced fluorescence of solid-state uranyl compounds

The combination of remote/standoff sensing and laser-induced fluorescence (LIF) spectroscopy shows potential for detection of uranyl (UO2(2+)) compounds. Uranyl compounds exhibit characteristic emission in the 450-600 nm (22,200 to 16,700 cm(-1)) spectral region when excited by wavelengths in the ultraviolet or in the short-wavelength portion of the visible spectrum. We report a parametric study of the effects of excitation wavelength [including 532 nm (18,797 cm(-1)), 355 nm (28,169 cm(-1)), and 266 nm (37,594 cm(-1))] and excitation laser power on solid-state uranium compounds. The uranium compounds investigated include uranyl nitrate, uranyl sulfate, uranyl oxalate, uranium dioxide, triuranium octaoxide, uranyl acetate, uranyl formate, zinc uranyl acetate, and uranyl phosphate. We observed the characteristic uranyl fluorescence spectrum from the uranium compounds except for uranium oxide compounds (which do not contain the uranyl moiety) and for uranyl formate, which has a low fluorescence quantum yield. Relative uranyl fluorescence intensity is greatest for 355 nm excitation, and the order of decreasing fluorescence intensity with excitation wavelength (relative intensity/laser output) is 355 nm > 266 nm > 532 nm. For 532 nm excitation, the emission spectrum is produced by two-photon excitation. Uranyl fluorescence intensity increases linearly with increasing laser power, but the rate of fluorescence intensity increase is different for different emission bands.     

Polarized fluorescence spectra of poly(ethylene terephthalate) films

The polarized excitation and fluorescence spectra of lowcrystalline, isotropic poly(ethylene terephthalate) (PET) film samples were measured in the glassy state at room temperature. Whereas the emission anisotropy r₀ of the excitation spectrum, recorded at the fluorescence maximum, changes sharply from 0.35 to 0 with decreasing wavelength in the region around 317 nm, the polarization of the fluorescence spectrum of PET is independent of wavelength. The fluorescence polarization of PET remains constant, if the temperature is increased up to 22 °C above T_g until the light scattering due to the crystallization causes complete depolarization. The photophysical behaviour supports the existence of a dilute solution of groundstate - stable sandwich dimers in the non-crystalline regions of PET.     

Two-dimensional fluorescence (excitation/emission) spectroscopy as a probe of complex chemical environments

We report a new application of fluorescence spectroscopy for the identification and characterization of chemical species in complex environments. Simultaneous collection of a dispersed fluorescence spectrum for every step of the laser wavelength results in a two-dimensional spectrum of emission versus excitation wavelengths. This two-dimensional fluorescence (2DF) spectrum yields quick and intuitive assignments of a multitude of peaks in the separate fluorescence excitation and dispersed fluorescence spectra as belonging to the same species. We demonstrate the technique with the measurement of 2DF spectra of a discharge of dilute benzene into a supersonic free jet. A multitude of rovibronic bands due to the C(2) Swan and C(3) comet bands are immediately apparent and even unreported bands can be assigned intuituvely. Custom software filters are employed to enhance or reject emission from one or the other carrier to obtain excitation spectra arising from purely one carrier, or even a specific spectral component of a single carrier. The very characteristic 2DF fingerprints of C(2) and C(3) permit identification of another unidentified species in the discharge that absorbs at 476 nm, coincident with one of the diffuse interstellar bands.     

Excitation wavelength dependence of the proton-transfer reaction of the green fluorescent protein

Picosecond time-correlated single-photon counting was used to measure the proton-transfer rate of green fluorescent protein (GFP) excited by several wavelengths between 266 and 405 nm. When samples of GFP in water and D2O are excited at short wavelengths, lambda(ex) < 295 nm, the fluorescence properties are largely modified with respect to excitation at a wavelength around 400 nm, the peak of the absorption band of the S0 --> S1 transition of the ROH form of the chromophore. The shorter the excitation wavelength, the longer the decay time of the ROH emission band at 450 nm and the longer the rise time of the RO- emission band at 512 nm. The proton transfer is slower by an order of magnitude and about a factor of 3 when GFP in water and D2O are excited by 266 nm, respectively.     

聚间亚苯亚乙烯的性能研究

自1990年Burroughes等首次报道聚对亚苯亚乙烯的电致发光以来,由于电致发光高分子材料在平面显示(特别是大面积显示)方面具有其他显示材料难以比拟的优势,因而近年来受到人们的广泛关注,在合成方法、加工性能、发光颜色的调控以及器件性能等多方面取得显著进展,不     

CHARACTERIZATION OF THE PHOTOREACTION BETWEEN DNA AND AMINOMETHYL-TRIMETHYLPSORALEN USING ABSORPTION AND FLUORESCENCE SPECTROSCOPY

–The use of absorption and fluorescence spectroscopy for following the progress of the photo-reaction between DNA and 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT) has been investigated. Absorption at long wavelengths and fluorescence both decline upon intercalation of AMT into the DNA helix. The loss of fluorescence from AMT and the accompanying appearance of monoadduct fluorescence upon irradiation by UV light can be easily followed by using the excitation beam of a spectro-fluorometer as the source of irradiation and monitoring the changing emission spectrum. Where cross-link formation is possible, the subsequent decline of monoadduct fluorescence is seen as well. This suggests that the 4,5-tnonoadduct is a precursor of cross-links. Both monoaddition and cross-linking are more rapid with poly d(A·T) than with calf thymus DNA or poly d(A·T). Excitation spectra can be helpful in resolving the levels of AMT and 4',5'-monoadduct when both are contributing to the emission spectrum. Some changes are observed in the emission spectrum of AMT–poly d(A·T) monoadducts after prolonged irradiation which indicate further photoreaction.     

Charge-transfer-type fluorescence of 4-(1H-pyrrol-1-yl)benzonitrile (PBN) and N-phenylpyrrole (PP) in cryogenic matrixes: evidence for direct excitation of the CT band

The fluorescence spectrum of PBN in a neat argon matrix is excitation-wavelength-dependent: at short excitation wavelengths, it consists of dual emission assigned to a charge-transfer (CT) state and a much weaker band assigned to the locally excited (LE) state. The CT emission is broad and almost completely devoid of vibrational structure, whereas the LE band is characterized by vibrationally resolved emission. At long excitation wavelengths, only CT emission is observed, indicating that the CT state is populated directly by light absorption and not via the LE state. Comparison with jet-cooled spectra of the bare molecule allows the unambiguous assignment of the LE spectrum and the location of the 0,0 band. The matrix LE emission spectrum is blue-shifted with respect to that of the gas phase, showing that the dipole moment of the LE state is smaller than that of the ground state. The fluorescence spectrum of PBN in an argon matrix does not change appreciably when acetonitrile (AN) is added to the matrix, in contrast to the case of N-phenylpyrrol (PP) (Schweke, D.; Haas, Y. J. Phys. Chem. A 2003, 107, 9554), for which addition of AN results in the appearance of two well separated emission bands. The different photophysical behaviors of PP and PBN in an argon matrix (and in supersonic jets) are analyzed by a simple model that considers the restriction of large-amplitude motions in the matrix. The implications of these low-temperature studies for understanding the properties of these systems in liquid solution are discussed.     

聚苯乙炔立体结构与光致发光性能关系的研究

使用有机金属铑、金属钨 /四苯基锡催化剂体系聚合苯乙炔 ,分别获得了高产率和高分子量的聚苯乙炔 .使用UV ,IR ,NMR ,GPC等分别对聚合物结构进行了表征 .采用不同波长的激发光对聚合物荧光性能进行研究 ,详细分析了聚合物结构与荧光性能之间的关系 .研究结果发现 ,不同聚合物结构对聚合物荧光性能产生很大影响 ,规整性高的聚合物 ,将有较高的发光量子效率 ;聚合物规整性差 ,将可能导致多个荧光发光结构点 ,其荧光强度降低 .聚合物荧光光谱研究将对某些共轭聚合物结构的规整性分析提供一些有用的信息     

EXCITED-STATE PROPERTIES OF DNA METHYLATED AT THE NV7 POSITION OF GUANINE AND ITS FREE FLUOROPHORE AT ROOM TEMPERATURE

The room-temperature optical properties of calf thymus DNA, with about 75% of its guanine residues methylated at position N-7, are compared with those of 7-methyl GMP which has the same fluorophore. The fluorescence spectrum of the methylated guanine residues depends strongly on the excitation wavelength, shifting to the blue as the wavelength increases. The fluorescence quantum yield, corrected for the contribution to absorption by the other virtually nonfluorescent residues, exhibits a pronounced drop at long excitation wavelengths relative to that for excitation at 265 nm. The degree of fluorescence polarization exhibits a weak dependence on the excitation and emission wavelengths. For 7-methyl GMP, the fluorescence spectrum is very weakly dependent on the excitation wavelength and its fluorescence quantum yield shows a moderate increase at long wavelengths. The degree of fluorescence polarization increases with increasing excitation wavelength particularly when monitoring the emission in the short wavelength region of the fluorescence spectrum. A pronounced drop of unknown origin is observed when exciting at 265 nm, which is not observed for methylated DNA. The methylated DNA data are interpreted in terms of a combination of (i) a heterogeneous environment of the methylated guanine residues, which results from sequence-dependent stacking interactions, and (ii) transfer of excitation energy from the other residues to the fluorescing methylated guanine residues. From the values of the quantum yields and those of the decay times, which we have recently reported (Georghiou et al., 1985), the following values are obtained for the radiative, k_t, and the sum of the nonradiative, σk₁, rate constants for deexcitation of the excited states of methylated DNA and its free fluorophore: 1.6 × 10⁸ s^-1 7 × 10⁷ s^-1 and 5 × 10¹⁰ s^-lvs 6 × 10⁹ s^-1. Because of energy transfer from the other residues. the k_f value for the methylated guanine residues is overestimated but their σk₁, value is not affected significantly and is by about an order of magnitude larger than that for 7-methyl GMP, apparently because of stacking interactions.     

Increased apparent sensitivity by means of constant-energy synchronous spectrofluorimetry

Synchronous fluorescence scanning at constant wavenumber (i.e., energy) difference between excitation and emission brings several improvements when compared to the classical spectrofluorimetry or to the method of synchrnous wavelength scanning. When quantitative results are required, the constant energy-difference technique should be used whenever the difference between the excitation and emission wavelengths exceeds the difference between the wavelengths of the Rayleigh and Raman peaks. Otherwise, the technique brings only minor advantages in comparison with synchronous wavelength scanning.     

Long-range assemblies on poly(dG-dC)2 and poly(dA-dT)2: phosphonium cationic porphyrins and the importance of the charge

The present paper describes synthesis and spectroscopic properties of novel cationic meso-tetraphenylporphyrins bearing two (trans) (P2) or three (P3) triphenylphosphonium substituents. The porphyrin aggregation in aqueous solutions is discussed in detail. Porphyrin binding to and self-organization onto long-range assemblies on poly(dA-dT)2 or poly(dG-dC)2 were probed by combination of absorption, fluorescence, circular dichroism (CD), transient and resonance light-scattering (RLS) techniques. The higher hydrophobicity of P2 is manifested by more extensive self-organization. Induced CD and intensive RLS indicate binding to the chiral environment on the nucleic acids exterior and exciton coupling between adjacent porphyrin moieties. The CD spectra of P2 on poly(dG-dC), and poly(dA-dT)2 suggest that the binding geometry is essentially independent of the base sequence. The fluorescence lifetime of about 4 ns was attributed to the long-range assembly. In the case of P3 the distinctly different CD spectra induced by GC or AT base-pair regions reveal that the number of the substituents determines how closely the porphyrin can approach the specific electronic environment on the nucleic acid exterior. The fluorescence lifetime of the P3 assembly is about 2 ns.     

烷氧基取代聚对苯发光性能的研究

聚对苯（ＰＰＰ）作为一个具有良好特性的导电聚合物材料很早便受到人们的青睐．进入九十年代后,它作为一种蓝色电致发光材料又受到人们的普遍注意．１９９２年,Ｇｒｅｍ等［１］采用Ｂａｌａｒｄ前驱聚合物法合成了ＰＰＰ并成功地用其制成了发光器件．１９９５年,他们...     

Short-wavelength fluorescence of 1,12-benzperylene

Two relatively strong bands, subband 1 and subband 2, observed in the short-wavelength region of the fluorescence spectrum of 1,12-benzperylene have been studied by varying the excitation wavelength and temperature and by adding n-hexane gas. In solution, subband 1 was observed at higher temperatures and can be attributed to an emission from a thermally-populated vibronic level of the first excited singlet state. In the gas phase, however, it is attributed to a υυ ? 1 resonance fluorescence. Subband 2 is attributed to fluorescence from the second excited singlet state.     

铽-依诺沙星-SDS敏化荧光猝灭法检测雷公藤红素

在pH 9.3的氨-氯化铵缓冲溶液中,铽(Ⅲ)能与依诺沙星、十二烷基硫酸钠(SDS)形成荧光配合物(λex=330 nm、λem=545 nm),SDS的存在能增强配合物的荧光强度。研究发现,在该反应体系中加入适量雷公藤红素溶液后,铽(Ⅲ)与依诺沙星络合物的激发、发射峰位置不变,但其荧光强度呈规律性下降。据此,建立了简单、快速、灵敏地测定雷公藤红素的荧光分析方法。雷公藤红素的浓度在5.2×10-6～8.4×10-5 mol/L范围内呈良好线性关系,方法的检出限为4.1×10-8 mol/L。     

侧链含氨基的聚(对亚苯基亚乙炔基-对亚苯基-咔唑)三元共聚物的合成及其聚集态下荧光特性

通过Sonogashira偶联反应制备了含有4-[2-(对苯胺)乙烯基]苯(M1)、2,5-二戊烷氧基-1,4-二乙炔基苯(M2)和9-辛基咔唑(M3)3种结构单元的三元共轭聚合物PPEC,并通过核磁共振氢谱确定了3种结构单元的比例为0.54∶1.00∶0.46(M1∶M2∶M3).由于在PPEC的侧链中含有氨基基团,通过在PPEC的THF溶液中分别加入水、甲醇和正己烷,诱导其产生聚集,其聚集后的荧光性质表现出明显的不同,在THF与水的混合溶剂中,PPEC发光强度会随着水含量的增加先是急剧降低,而后在高水含量时发光强度又显著增强;在THF与甲醇的混合溶剂中,PPEC发光强度随着甲醇的加入只是逐渐降低;在THF与正己烷的混合溶剂中,PPEC的发光强度则会随着正己烷的增加而增强.该结果表明氨基通过与水,或者自身所形成氢键作用,改变了PPEC分子链之间的聚集态结构,降低了分子内旋转非辐射能量效率,从而有效改善共轭聚合物的主链发光性质,这为设计聚集态下(或固态下)高性能的荧光共轭聚合物提供了一种新思路.     

Yb3+和Er3+共掺的GdAlO3荧光粉体的发光性质研究

采用溶胶-凝胶法制备了Yb3+和Er3+掺杂的GdAlO3荧光粉体.XRD结果表明样品为正交晶系结构.研究了不同波长激发下的室温发射光谱以及上转换发光光谱.结果表明样品在1550 nm处有很强的荧光发射,并且在样品中存在显著的Yb3+到Er3+之间的能量传递过程.980 nm红外光激发下的上转换发光光谱表明样品有绿色和...