Polarized fluorescence spectroscopy

In addition to fluorescence intensity and polarization, fluorescence spectroscopy also includes measurement of the lifetime of the excited state. Recent improvements in the design of fluorescence instrumentation for measuring fluorescence lifetime have permitted additional applications of fluorescence techniques to immunoassays. Fluorescence lifetime measurement can be performed by either phase-resolved or time-resolved fluorescence spectroscopy. 

III. Chirality of excimers as observed with circularly polarized fluorescence spectroscopy, 203... 

III. CHIRALITY OF EXCIMERS AS OBSERVED WITH CIRCULARLY POLARIZED FLUORESCENCE SPECTROSCOPY... 

Fisz, J. J., 1996, Polarized fluorescence spectroscopy of two ground and two-excited state systems in solutions, Chetn. Phys. Lett. 262 495-506. 

The decrease of x with decreasing X was explained by the correlation of the transition energy AE with the Einstein coefficient A= 1/Xo (AE) X" [2, 5]. A long-lived fluorescence component with x>100 is was interpreted by a weak coupling between some levels of the A Ai and X states [6]. A very short radiative lifetime of the (0,10,0)i level, x = 0.35 ps, measured by polarized fluorescence spectroscopy [11], is in disagreement with x = 18 4 ps... 

Ikkai, T. Arii, T. Shimada, K. Excimer fluorescence as a tool for monitoring protein domain dynamics applied to actin conformation changes based on circulatory polarized fluorescence spectroscopy. J. Fluoresc. 2006,16, 367-374. 

The attachment of pyrene or another fluorescent marker to a phospholipid or its addition to an insoluble monolayer facilitates their study via fluorescence spectroscopy [163]. Pyrene is often chosen due to its high quantum yield and spectroscopic sensitivity to the polarity of the local environment. In addition, one of several amphiphilic quenching molecules allows measurement of the pyrene lateral diffusion in the mono-layer via the change in the fluorescence decay due to the bimolecular quenching reaction [164,165]. 

Intermediate methods include the earliest procedure based on Stein s equation [33] and one based on Samuels equation [34]. Among the direct methods is an IR spectroscopic method based on the measurement of the dichroic ratio (R), of amorphous absorption bands. In the investigations [35], the amorphous bands 898 cm" and 1368 cm", for which the angles of transition moment are a898 = 39 and aneg = 80 , respectively, were used. Other methods are spectroscopy of polarized fluorescent radiation [35,36], measurement of color di-... 

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

Fluorescence spectroscopy is also particularly well-suited to clarify many aspects of polymer/surfactant interactions on a molecular scale. The technique provides information on the mean aggregation numbers of the complexes formed and measures of the polarity and internal fluidity of these structures. Such interactions may be monitored by fluorescence not only with extrinsic probes or labelled polymers, but also by using fluorescent surfactants. Schild and Tirrell [154] have reported the use of sodium 2-(V-dodecylamino) naphthalene-6-sulfonate (SDN6S) to study the interactions between ionic surfactants and poly(V-isopropylacrylamide). 

Polarized Raman and fluorescence spectroscopies, NMR and X-ray diffraction allow the determination of at least (P2) and (P4) for uniaxial systems. This is a great advantage since the shape of the orientation distribution can then be estimated [7], even if not all the coefficients of the ODF s expansion are known. While P2 has fixed boundary limits, those of (P4) depend on the (P2) value such as... 

Like Raman scattering, fluorescence spectroscopy involves a two-photon process so that it can be used to determine the second and the fourth rank order parameters. In this technique, a chromophore, either covalently linked to the polymer chain or a probe incorporated at small concentrations, absorbs incident light and emits fluorescence. If the incident electric field is linearly polarized in the e direction and the fluorescent light is collected through an analyzer in the es direction, the fluorescence intensity is given by... 

Other optical and spectroscopic techniques are also important, particularly with regard to segmental orientation. Some examples are fluorescence polarization, deuterium nuclear magnetic resonance (NMR), and polarized IR spectroscopy [4,246,251]. Also relevant here is some work indicating that microwave techniques can be used to image elastomeric materials, for example, with regard to internal damage [252,253]. 

Vukjovic et al.199 recently proposed a simple, fast, sensitive, and low-cost procedure based on solid phase spectrophotometric (SPS) and multicomponent analysis by multiple linear regression (MA) to determine traces of heavy metals in pharmaceuticals. Other spectroscopic techniques employed for high-throughput pharmaceutical analysis include laser-induced breakdown spectroscopy (LIBS),200 201 fluorescence spectroscopy,202 204 diffusive reflectance spectroscopy,205 laser-based nephelometry,206 automated polarized light microscopy,207 and laser diffraction and image analysis.208... 

Droplet temperature is of interest in practical spray processes since it influences the associated heat and mass transfer, chemical reactions, and phase changes such as evaporation or solidification. Various forms of Rayleigh, Raman and fluorescence spectroscopies have been developed for measurements of droplet temperature and species concentration in sprays.16471 Rainbow refractometry (thermometry), polarization ratioing thermometry, and exciplex method are some examples of the droplet temperature measurement techniques. 

Another advantage to examine these polyaers is that characterizations of ablated materials can be Bade possible by fluorescence spectroscopy. Fluorescence is very sensitive, and such surrounding aicroenvironaental conditions around the it -chromophore as polarity and viscosity and chroaophore aggregation can be probed. 

Until recently, previous studies for continuous monitoring of hepatic function with ICG utilized the absorption mode. However, new studies demonstrate that the highly sensitive fluorescence technique can equally be used [148-150]. In addition to high sensitivity, in-depth analysis of the emission, excitation and polarization properties of fluorescence spectroscopy furnishes additional functional information about the dye molecule. In this system, the fluorescence profile emanating from the clearance of injected biocompatible dye is monitored with a small photodetector. Fig. 8 shows the in vivo fluorescence detection apparatus developed for continuous monitoring of organ functions [147,148]. 

Time-resolved fluorescence spectroscopy of polar fluorescent probes that have a dipole moment that depends upon electronic state has recently been used extensively to study microscopic solvation dynamics of a broad range of solvents. Section II of this paper deals with the subject in detail. The basic concept is outlined in Figure 1, which shows the dependence of the nonequilibrium free energies (Fg and Fe) of solvated ground state and electronically excited probes, respecitvely, as a function of a generalized solvent coordinate. Optical excitation (vertical) of an equilibrated ground state probe produces a nonequilibrium configuration of the solvent about the excited state of the probe. Subsequent relaxation is accompanied by a time-dependent fluorescence spectral shift toward lower frequencies, which can be monitored and analyzed to quantify the dynamics of solvation via the empirical solvation dynamics function C(t), which is defined by Eq. (1). 

Steady-state and multifrequency phase and modulation fluorescence spectroscopy are used to study the photophysics of a polar, environmentally-sensitive fluorescent probe in near- and supercritical CF3H. The results show strong evidence for local density augmentation and for a distribution of cluster sizes. These results represent the first evidence for lifetime distributions in a "pure solvent system. 

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