Polarity effects on wavelength dependence of the fluorescence quantum yield for indole

The change in fluorescence quantum yield for indole as a function of excitation wavelength between 250 and 220 nm is found to vary with the static dielectric constant of various alcohol—water mixtures at 296 K. The supports the intermediacy of a CTTS state in the photoionization process.     

Rotational-level dependence of the fluorescence yield of pyrazine: Computer simulation of the quantum yield spectrum

The slow-fluorescence quantum yield spectrum along the rotational contour of the 0-0 absorption band of pyrazine is simulated using an asymmetric rotor     

Fluorescence quantum yield of the two novel macrocyclic lactams

Fluorescence quantum yield of two novel compounds—dibenzo[c,k]-1,2-dithia-6,9-diazacyclododecane-5,10-dione (1) and dibenzo[c,k]-1,2-dithia-6,9-diaza-7-methylcyclododecane-5,10-dione (2) was studied by Williams method using anthracene as a reference.     

量子点标记荧光免疫分析测定雌三醇

采用包被雌三醇完全抗原竞争免疫分析模式,以量子点标记羊抗兔抗体为荧光探针,建立了一种测定雌三醇的量子点标记的荧光免疫分析新方法.方法测定雌三醇的线性范围为0.01～10 000μg/L;检出限为0.007 5μg/L.此法用于尿液样品的分析,并利用高效液相色谱法进行对照,测定结果一致。     

Temperature dependence of fluorescence quantum yield,decay time and intersystem crossing activation energy of 9-acetoxy-10-acetoxyhalogenphenylanthracene derivatives

Temperature dependence studies of the fluorescence quantum yield and decay time on 9-acetoxy-10-halogenphenylanthracene derivatives have been carried out. The activation energy for intersystem crossing processes increases with the atomic number of the halogen atom substituted, independent from the position of the heavy atom in the phenyl ring. The fluorescence rate constant k_F depends on the temperature only for those compounds with a substituted heavy atom. The k_F− values determined from i) absorption measurements and ii) quantum yield and decay time fluorescence are in good correspondence. The internal conversion rate has turned out to be insignificant.     

Fluorescent quantum yield of pyrene probe in ultrathin polymer films

The fluorescently labelled polymers including pyrene-labelled polystyrene (PyPS) and pyrene-labelled poly(methyl methacrylate) (PyPMMA) with narrow molecular weight distributions were synthesized by the atom transfer radical copolymerization (ATRCP) of styrene or methyl methacrylate with 1-pyrenemethyl methacrylate (PyMMA). The ultrathin PyPS and PyPMMA films with the thickness ranging from 30 nm to 400 nm supported on the quartz slides were prepared by spin-coating. The fluorescent quantum yield (QY) of the pyrene probe in the ultrathin polymer films was investigated by the photoluminescence spectrometer using an integrating sphere detector. The QY decreased with the reduction of film thickness in the sub-200 nm range.     

Relative quantum yield of the S2 → S1 fluorescence from azulene

The quantum yield ratio r = φ_{2 → 0}/φ_{2 → 1} of the S₂ → S₀ and S₂ → S₁ fluorescences from azulene has been redetermined. With azulene in isopentane at 190 K, r = 455 ± 100. This value agrees with the lower limit, given by Huppert, Jortner and Rentzepis, but is an order of magnitude lower than that given by Gillispie and Lim.     

Fluorescence enhancement method for the determination of nucleic acids using cationic cyanine as a fluorescence probe

A fluorescence enhancement method with a cationic cyanine as a probe was developed for the determination of nucleic acids. Under the experimental conditions, the fluorescence enhancement of cyanine (lambda(ex)/lambda(em)= 524/591.5 nm) was observed in the presence of DNA. The calibration graphs were linear over the range of 0.01-15 microg mL(-1) for both calf thymus DNA (CT DNA) and fish sperm DNA (FS DNA). The limits of detection were 0.005 and 0.007 microg mL(-1) for CT DNA and FS DNA, respectively. The method was applied to the determination of DNA in synthetic and real samples and satisfactory results were obtained. A possible fluorescence enhancement mechanism was also studied.     

Viscosity dependence of the denitrogenation quantum yield in azoalkane photolysis: experimental evidence for reversible formation of the diazenyl diradical

[reaction: see text] Experimental evidence is reported for the reversible formation of the singlet diazenyl diradical ((1)DZ), photolytically generated from the structurally elaborate DBH-type azoalkane. Reversiblity of the (1)DZ formation manifests itself through the decrease of the photodenitrogenation quantum yield over a ca. 40-fold viscosity variation (from 0.5 to 19.3 cP). This viscosity behavior is interpreted in terms of frictional effects on the competitive reaction modes of the diazenyl diradical.     

Rotational effects on the quantum yield and lifetime of the slow component of fluorescence from s-triazine

The fluorescence quantum yield and lifetime of the slow component of fluorescence obtained along the rotational contour of the 6¹₀ and 6²₀ absorption bands of s-triazine at low pressure show a marked variation. For each band, the quantum-yield spectrum shows a sharp peak at the Q-branch edge, the lifetime spectrum exhibits a valley at the same position.     

Fluorescence ratiometry and fluorescence lifetime imaging: using a single molecular sensor for dual mode imaging of cellular viscosity

Intracellular viscosity strongly influences transportation of mass and signal, interactions between the biomacromolecules, and diffusion of reactive metabolites in live cells. Fluorescent molecular rotors are recently developed reagents used to determine the viscosity in solutions or biological fluid. Due to the complexity of live cells, it is important to carry out the viscosity determinations in multimode for high reliability and accuracy. The first molecular rotor (RY3) capable of dual mode fluorescence imaging (ratiometry imaging and fluorescence lifetime imaging) of intracellular viscosity is reported. RY3 is a pentamethine cyanine dye substituted at the central (meso-) position with an aldehyde group (CHO). In nonviscous media, rotation of the CHO group gives rise to internal conversion by a nonradiative process. The restraining of rotation in viscous or low-temperature media results in strong fluorescence (6-fold increase) and lengthens the fluorescence lifetime (from 200 to 1450 ps). The specially designed molecular sensor has two absorption maxima (λ(abs) 400 and 613 nm in ethanol) and two emission maxima (in blue, λ(em) 456 nm and red, 650 nm in ethanol). However it is only the red emission which is markedly sensitive to viscosity or temperature changes, providing a ratiometric response (12-fold) as well as a large pseudo-Stokes shift (250 nm). A mechanism is proposed, based on quantum chemical calculations and (1)H NMR spectra at low-temperature. Inside cells the viscosity changes, showing some regional differences, can be clearly observed by both ratiometry imaging and fluorescence lifetime imaging (FLIM). Although living cells are complex the correlation observed between the two imaging procedures offers the possibility of previously unavailable reliability and accuracy when determining intracellular viscosity.     

水溶性CdSe量子点的合成及其作为荧光探针对大肠杆菌的快速检测

采用水相法以谷胱甘肽为稳定剂合成高稳定性的CdSe量子点,利用化学偶联剂的作用使得量子点表面基团与菌体之间的成功结合,对偶联的条件进行了优化.基于荧光分析法建立了一种快速简便的大肠杆菌检测定量分析方法.研究结果表明:合成的量子点具有稳定、荧光性能良好等突出优点.通过偶联剂量子点能与大肠杆菌结合,其荧光强度与大肠杆菌浓度...     

Structure of the phonon sidebands in the t1 → s0 transition of naphthalene in p-dibromobenzene, α-phase p-dichlorobenzene,and γ-phase p-dichlorobenzene host crystals

The theory used for predicting the intensity distributions in phonon sidebands in the electronic spectra of molecular crystals is briefly reviewed with particular emphasis on chemically mixed crystals. Criteria are suggested for the identification of pseudolocalized features in phonon sidebands. The phonon sidebands associated with the phosphorescence of naphthalene in p-dibromobenzene and α-phase p-dichlorobenzene seem to exhibit some degree of localization, while the phonon sideband of the phosphorescence of naphthalene in γ-phase p-dichlorobenzene appears to be entirely delocalized. The results are compared with those of other workers and a correlation is established between the degree of localization and the strength of the exciton-phonon coupling as measured by the optical Debye-Waller factor. It is further shown that the strength of coupling of the phonons to the electronic transition is independent of the gas-to-crystal shift of the impurity.     

Pressure dependence for the CO quantum yield in the photolysis of acetone at 248 nm: a combined experimental and theoretical study

The quantum yield of CO in the laser pulse photolysis of acetone at 248 nm and at 298 K in the pressure range 20-900 mbar (N2) has been measured directly using quantitative infrared diode laser absorption of CO. It is found that the quantum yield of CO shows a significant dependence on total pressure with Phi(CO) decreasing with pressure from around 0.45 at 20 mbar to approximately 0.25 at 900 mbar. From a combination of ab initio quantum chemical calculations on the molecular properties of the acetyl (CH3CO) radical and its unimolecular fragmentation as well as the application of statistical (RRKM) and dynamical calculations we show that CO production results from prompt secondary fragmentation (via(2a)) of the internally excited primary CH3CO* photolysis product with an excess energy of approximately 62.8 kJ mol(-1). Hence, our findings are consistent with a consecutive photochemically induced decomposition model, viz. step (1): CH3COCH3+hv--> CH3CO*+ CH3, step (2a): CH3CO*--> CH3+ CO or step (2b) CH3CO*-(+M)--> CH3CO. Formation of CO via a direct and/or concerted channel CH3COCH3+hv--> 2CH(3)+ CO (1') is considered to be unimportant.     

The concentration dependence of the reduced viscosity for a spherical,non-expanding macroion

Summary The variation of the reduced viscosity with solvent dilution was investigated for a non-expanding sulphonated polystyrene latex. Based on previous measurements of the primary and secondary electroviscous effects, an empirical equation was derived forη _sp/c in terms of the concentration of the latex and the ionic strength of the solvent. Validity of the equation was confirmed by quantitative agreement of the predictedη _sp/c with the experimental values at several ionic strengths. Various factors, determining the shape of the solvent dilution curve, were discussed. The results suggested that the upsweep of theη _sp/c and the occurrence of a maximum at low ionic strength can no longer be regarded as the exclusive characteristic of the molecular expansion of a linear flexible macroion.

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Zusammenfassung Es wird die Variation der reduzierten Viskosit?t mit der L?sungsmittelverdünnung für nicht expandierende sulfonierte Polystyrollatex untersucht. Basierend auf vorangehenden Messungen des prim?ren und sekund?ren elektroviskosen Effekts wird eine empirische Gleichung fürη _sp/c in Termen der Konzentration der Latex- und der Ionenst?rke des L?sungsmittels abgeleitet. Die Gültigkeit der Gleichung wird durch quantitative übereinstimmung des vorausgesagtenη _sp/c mit den experimentellen Werten bei mehreren Ionenst?rken best?tigt. Verschiedene Faktoren, die die Gestalt der Abh?ngigkeit der Kurve von der Konzentration des L?sungsmittels bestimmen, werden diskutiert. Die Ergebnisse legen nahe, da? der Anstieg derη _sp/c und das Auftreten eines Maximums bei kleinen Ionenst?rken nicht l?nger als ein ausschlie?liches Charakteristikum für Molekularexpansion von linearen flexiblen Makroionen betrachtet werden darf.

     

The dependence of fluorescence quantum yields on the exciting wavelength in solutions of rare earth ions

The conditions are discussed under which quantitative results can be obtained on fluorescent yields in solutions of rare earth ions, and Eu³⁺ in particular. It is shown that fluorescent quantum yields may depend on the wavelength of excitation.     

Temperature dependence of the fluorescence quantum yields of diphenylsiloxane‐based copolymers in dilute solutions

The monomer and excimer fluorescence quantum yields of well‐defined poly(dimethylsiloxane‐co‐diphenylsiloxane)s with different diphenylsiloxane (Ph₂SiO) contents have been determined, along with those of 1,1,3,3‐tetraphenyl‐1,3‐dimethyldisiloxane and 1,1,3,3,5,5‐hexaphenyltrisiloxane‐1,5‐diol used as model compounds, in a dilute organic solvent at different temperatures. The measured fluorescence quantum yields of the copolymers are correlated with the fraction of the ? (CH₃)₂SiO? (Ph₂SiO)_n? (CH₃)₂SiO? structures. The monomer fluorescence yield for copolymers with low Ph₂SiO contents is dominated mainly by the isolated ? (CH₃)₂SiO? (Ph₂SiO)? (CH₃)₂SiO? unit, and the apparent mean binding energy of the excimer does not increase significantly with increasing Ph₂SiO content. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 854–861, 2002     

Short-wavelength fluorescence caused by sequential two-photon excitation of some cyanine dyes: Effect of solvent viscosity on the quantum yields

Short-wavelength (SW) fluorescence of some cyanine dyes caused by sequential two-photon excitation was studied. The fluorescence quantum yield of the SW fluorescence shows a significant dependence on the solvent viscosity, but only a small dependence on temperature. This reveals the dynamic character of the emitting state: much lower intramolecular barrier and larger solute-solvent viscous drag compared to the S₁ state in the molecular conformational change which is important as a radiationless decay channel.