Anisotropy absorption

Blessing, R.H. (1995) An empirical correction for absorption anisotropy, Acta Cryst. A, 51, 33-38. 

The electronic structure of fluorenes and the development of their linear and nonlinear optical structure-property relationships have been the subject of intense investigation [20-22,25,30,31]. Important parameters that determine optical properties of the molecules are the magnitude and alignment of the electronic transition dipole moments [30,31]. These parameters can be obtained from ESA and absorption anisotropy spectra [32,33] using the same pump-probe laser techniques described above (see Fig. 9). A comprehensive theoretical analysis of a two beam (piunp and probe) laser experiment was performed [34], where a general case of induced saturated absorption anisotropy was considered. From this work, measurement of the absorption anisotropy of molecules in an isotropic ensemble facilitates the determination of the angle between the So Si (pump) and Si S (probe) transitions. The excited state absorption anisotropy, rabs> is expressed as [13] ... 

The values of /labs were determined from the experimentally measured absorption anisotropy with Eq. 6. In viscous polyTHF, the rotational movement of dye molecules on a lOOps time scale is assumed to be negligible, and thus, does not reduce the limiting value of anisotropy. For the concentrated fluorene solutions (5 x 10 M, 1 mm cuvette), the anisotropy Tabs was not affected by FOrster depolarization mechanisms [13] due to the short time delay, tD, between probe and pump pulses when td/ti 1 [35]. 

Fig. 14 Excited state absorption (AD (1), ADx (2)) and absorption anisotropy (3) spectra of compoiuids 16 (a) and 22 (b) in polyTHF...

In the work by Willemsen and co-authors [84] the three Stokes polarization parameters were studied during polarization switches in a vertical-cavity semiconductor laser. It was demonstrated that when the linear part of the absorptive anisotropy is close to zero [127], the laser is bistable and switches stochastically between two polarisations [128]. The analysis of large fluctuations of polarizations in this system [84] reveals what authors have called a stochastic inversion symmetry (see Fig. 10), which is analogous to the time-reversal symmetry observed for the model (17) and shown in Fig. 7. 

Reid PJ, Silva C, Walhout PK, Barbara PE. (1994) Femtosecond absorption anisotropy of the aqueous solvated electron. Chem Phys Lett 228 658-664. 

The wide range of values of the ratio of MCD to absorption forms the basis of another practical, albeit rarely used, application in biophysical spectroscopy. Molecules with a characteristic MCD spectrum and high MCD/absorption anisotropy in a limited spectral region (heme proteins are a good example) can be detected and quantified in complex mixtures that exhibit continuous absorption and scattering of light across the spectrum, such as crude cell or tissue extracts.This use of MCD is similar to one-beam, two-wavelength absorption difference spectroscopy, which is widely used in studies of metabolism and the biochemistry of heme proteins. ... 

The absorbance A of polarized light is directly correlated to concentration and absorption anisotropy of molecules through the Lambert-Beer law ... 

As previously described (1,6), we used eosinisotbio(7anate (EITC), covalently attached to dmerent sites in OF jCFy as a triplet mobe for measuring the protein rotational diffusion via absorption anisotropy. CF C was labelled after... 

Figure 3. Time course of the absorption anisotropy for the ETTC labelled CFOCFl reconstituted in Uposomes.

Figure 3 shows a typical curve obtained for the decay of the absorption anisotropy. The shown measurement was performed at 30 C and the proteoliposomes were contained in aequous buffer solution (tisfl mPa S). In all measurements with subunit m labelled CFgCFj in liposomes die decay of the absorption anisotropy could only be fitted by two exponentials according to equation 1 (Materials and Methods section). 

As shown elsewere (7) the observed decay of the absorption anisotropy can be attributed to anisotropic rotation of the protein in the bilayer membrane. The mathematical analysis of the curve shown in figure 2 according to equation 1 yielded the following parameters initial anisotropy rQ=0.17 aj=0.045 32=0.12 4>j=200 ns 2=50ns. 

Absorption anisotropy (dichroism) in liquid crystals takes place either due to the presence of the short wavelength (< 400 nm) oscillator, usually coinciding with the direction of its long molecular axis, or due to the impurities, such as dichroic dyes ( guests ) dissolved in liquid crystals ( hosts ). We will consider the second case as the most important for practical applications ( guest-host effect [18]). 

Park etal. assumed the chevron structure as shown in Fig. 6.3.28 based on the results of X-ray measurements. They argued that the effective birefrengence, switching current, second harmonic generation and IR absorption anisotropy measured for this phase could be explained by the model as shown in Fig. 6.3.28. 

IR absorption anisotropies of the phenyl ring vibration mode at 1605 cm for the SmA phase and the frustoelectric phase without applied voltage show that the molecular ordering in this phase at zero field is almost the same as that in SmA phase. Furthermore, the maxima and minima of the IR absorption anisotropies under the electric field do not change from those at zero field. These phenomena mean that the molecular distribution at zero voltage is the same as that under the electric field. These phenomena including the chevron structure can only be explained by the model shown in Fig. 6.3.28 [46]. 

The use of the picosecond technique enabled Pouligni et al. to observe the reorientation kinetics of 3,3 -diethyloxadicarbocyanine by absorption anisotropy in microemulsions of Aerosol OT (AOT) and methyl alcohol in cyclohexane [84, 85]. 

Observable in time-resolved absorption anisotropy measurements, and not as spectral shift or population decay. 

Fig. 14. Time dependence of the absorption anisotropy of RuN3 in EtOH solution at 850 nm. Inset the same data at early times together with the scaled absorption anisotropy of the RuN3-sensitized Ti02 film. Symbols are measured data, curves are fits to the signals with the following time constants RuN3-EtOH 65 10 fs, 19+2 ps, and >250 ps RuN3-TiOs-CHjCN 30+10 fs.

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