Fluorescence polarizer orientation

Nobbs, J. H., Ward, I. M. Polarized fluorescence in oriented polymers, in Photoluminescence of Synthetic Polymers (ed.) Phillips, D. C. Chap. 7, Chapman Hall Ltd., London (1984)... 

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]. 

B. Schartel, Y. Wachtendorf, M. Grell, D.D.C. Bradley, and M. Hennecke, Polarized fluorescence and orientational order parameters of a liquid-crystalline conjugated polymer, Phys. Rev. B, 60 277-283, 1999. 

We have considered spherical molecules so far, but it should be noted that isotropic rotations can also be observed in the case of molecules with cylindrical symmetry and whose absorption and emission transition moments are parallel and oriented along the symmetry axis. In fact, any rotation around this axis has no effect on the fluorescence polarization. Only rotations perpendicular to this axis have an effect. A typical example is diphenylhexatriene whose transition moment is very close to the molecular axis (see Chapter 8). 

The fluorescence polarization technique is a very powerful tool for studying the fluidity and orientational order of organized assemblies (see Chapter 8) aqueous micelles, reverse micelles and microemulsions, lipid bilayers, synthetic non-ionic vesicles, liquid crystals. This technique is also very useful for probing the segmental mobility of polymers and antibody molecules. Information on the orientation of chains in solid polymers can also be obtained. 

D. Axelrod, Carbocyanine dye orientation in red cell membrane studied by microscopic fluorescence polarization, Biophys. J. 26, 557-573 (1979). 

As soon saturation occurs, those ground-state molecules with p // die out first. This can be detected by observing the corresponding decrease in the fluorescence polarization. Fig. 12 shows the experimental results. This proves that the optical pumping by laser light is even faster than the relaxation rate between molecules of different spatial orientation. 

If the molecules are placed in a magnetic field, the different spatial orientations correspond to different Zeeman levels and the selective saturation explained above leads to a nonthermal population of the Zeeman niveaus. By exposing the sample simultaneously to an rf field with the proper frequency, magnetic dipole transitions between the Zeeman levels can occur and the thermal population can be restored. This will again increase the polarization of the fluorescence at most up to its presaturation value. The fluorescence polarization is thus used as detector for the rf transitions. 

The emitted light is detected along y through a polarizer oriented either along z (Fz) or along x (Fx). In fluorescence polarization studies with continuous excitation (steady-state experiments), the emission anisotropy r and the emission polarization p are defined in eqs 8a and 8b. 

The fluorescence polarization spectrum of Rhodamin B and the SoFresponding absorption spectrum are given in the Figure 4.17B. The transition in bands 1 and 5 have the same polarization direction, bands 3 pud 4 are polarized almost perpendicular to 1 and the polarization of 2 gjt at some intermediate angle. These reflect the relative orientation of phe transition moments in the respective bands. 

P. Lapersonne, J.-F. Tassin, P. Sergot, andL. Monnerie, Fluorescence polarization characterization of biaxial orientation, Polymer, 30,1558 (1989). 

Circular polarization of luminiscence, stopped-flow fluorescence, fluorescence-monitored chemical relaxation, the evaluation of relative orientation by polarized excitation energy transfer, time-resolved fluorescent polarization ( nanosecond polarization ), and other new techniques have become valuable means for studying protein structures, their interactions and structural changes in relation to various treatments (e.g. denaturation). New fluorescent probes and quenchers have enabled the research field to expand from isolated proteins to more complicated systems such as membranes, muscle and nerve components and other subcellular structures (see also 7.3). 

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