Electric field fluorescence yield

A major advantage of fluorescence as a sensing property stems from the sensitivity to the precise local environment of the intensity, i.e., quantum yield (excited state lifetime (xf), and peak wavelength (Xmax). In particular, it is the local electric field strength and direction that determine whether the fluorescence will be red or blue shifted and whether an electron acceptor will or will not quench the fluorescence. An equivalent statement, but more practical, is that these quantities depend primarily on the change in average electrostatic potential (volts) experienced by the electrons during an electronic transition (See Appendix for a brief tutorial on electric fields and potentials as pertains to electrochromism). The reason this is more practical is that even at the molecular scale, the instantaneous electric... 

The essence of the XSW technique now lies in the effect these modulations have on the photoelectric cross-section of a target atom a distance c above the mure surface. The incident X-rays can eject a core electron from the atom so generating a vacancy and resulting in the emission of a fluorescent X-ray photon The probability of an incident photon ejecting the core electron, the photoelectric cross-section, is directly proportional to the electric field experienced by the atom Hcncc. the fluorescence yield, T(0.for an atom or ion distribution A (z) a distance above the mirror surface can be written... 

Forster energy transfer or energy transfer at a distance occurs between two molecules, a donor (the excited fluorophore), and an acceptor (a chromophore or fluorophore). Energy is transferred by resonance, i.e., the electron of the excited molecule induces an oscillating electric field that excites the acceptor electrons. As a result of this energy transfer, the fluorescence intensity and quantum yield of the emitter will decrease. Energy transfer is described in Chapter 14. 

To understand the importance of spectral overlap to metal-enhanced fluorescence, it is useful to review the basics of metal-enhanced fluorescence. Metal nanostructures can alter the apparent fluorescence from nearby fluorophores in two ways. First, metal nanoparticles can enhance the excitation rate of the nearby fluorophore, as the excitation rate is proportional to the electric field intensity that is increased by the local-field enhancement. Fluorophores in such "hot spots" absorb more light than in the absence of the metal nanoparticle. Second, metal nanoparticles can alter the radiative decay rate and nonradiative decay rate of the nearby fluorophore, thus changing both quantum yield and the lifetime of the emitting species. We can summarize the various effects of a nanoparticle on the apparent fluorescence intensity, Y p, of a nearby fluorophore as ... 

Gold nanoparticies can modify the emission of dipole fluorophores through dipole-dipole interactions that are dependent on the gold particle size, shape, and distance from the fluorophore. Further, the effect is dependent on the orientation of the molecular dipole with respect to the particle and the overlap of the emission of the molecule with the particle s absorption spectrum [17]. Either quenching or enhancement of the fluorescence may occur depending on the various parameters that determine the quantum yield of the emission of the fluorophore molecules. These parameters include the excitation electric field E, the radiative rate k, and nonradiative rate k. ... 

Ono and Ware"" have measured the absorption, emission, and excitation spectra, the fluorescence decay times, and the quantum yields of a series of substituted diphenylmethylenes in rigid matrices at low temperatures. Acean-thrylene shows S2- So emission in hexane with a yield of 0.017 and lifetime of 4.3 ns. The low-temperature fluorescence spectra of bis-2-naphthyl-alkanes and their derivatives have been studied. Excimer formation is an activated process. The fluorescence and absorption spectra of 1,1-diphenyl-ethylenes have been analysed in some detail by Gustav and Bolke. " The S — Si transitions in trans isomers of phenylnaphthylethylenes have been assigned by picosecond absorption spectroscopy. Effects of solvent viscosity and the role of conformers in the mechanism of isomerization are elucidated. The production of non-equilibrium conformer concentrations in glassy solutions of diarylethylenes at 77 K due to restrictions imposed by the solid matrix has also been reported. Free jet excitation and emission spectra of diphenyl-butadiene show clearly the lowest excited Ag state and give a lifetime of 52.8 ns for 0-0 excitation.Electric field-induced charges in the optical... 

Paper, or cellulose, electrophoresis was introduced in the early 1950s as a separation technique for proteins. Prior to the start of the electrophoretic run, the cellulose sheet is saturated with the running buffer and placed in a tank, as shown in Figure 9.5. The sample is then applied as a spot or a line, the tank is covered and the electric field is applied. After the separation has proceeded for a sufficient time, the paper is removed and dried. The separated components are then located by color, by fluorescence under UV light, or after staining with a dye. If the components have been radiolabeled, autoradiography of the entire paper will yield a separation pattern. 

M. E. (1991) Excitation dichroism of electric field modulated fluorescence yield for the identification of primary electron acceptor in photosynthetic reaction center. /. Phys. Chem., 95, 2036-2041. 

A comprehensive review of hole burning spectroscopy of species in glasses has been prepared by Haarer and Silbey. Electric field effects on the spectral holes for perylene in Shpol skii matrices in n-heptane provide a useful extension of this technique . The limitations of the thermal lens method for the measurement of fluorescence yields have been examined and discussed . It is pointed out that the... 

Figure 25 depicts the angular dependence of the electric field and fluorescence yield for an adsorbate layer located at varying positions with respect to the diffracting planes. The phase and amplitude of this modulation (or so-called coherent position and coherent fraction) are a measure of the mean position and width of the distribution of atoms in the overlayer. The... 

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