Absorption polarized

Tabic 6-3. Vibrational assignment of the b- and c-polarized absorption spectra of T6 single crystal at 4.2 K. The proposed assignment is in agreement with the most intense vibrational modes found by Bimbaum et al. [64] in the excitation spectra of matrix isolated tetralhiophene (T4) at low temperature. 

In order to summarize this section it must be noted that the possibility to evaporate conjugated oligomers in such a way that their chain axes point predominantly in one direction allows us to determine the anisotropic electronic properties of conjugated molecules. From these studies it becomes evident that in order to obtain polarized absorption or emission of light as required in polarization Filters or LCD-backlights, the application of conjugated molecules is one of the most attractive areas of application for these materials. 

The b-polarized absorption bands (see Fig. 6-3b) at 20945 cm 1, 22250 cm-1 and 23535 cm-1 are assigned to a vibronic progression built on the bu Davydov component with the totally symmetric mode at 1275 cm-1. 

We examined the magnetic orientation or organization of the SWNTs or the polymer-wrapped SWNTs using MEHPPV by measurements of AFM images and polarized absorption spectra [46-48]. 

Figure 15.2 Polarized absorption spectra of SWNT/MEHPPV composites on glass plates in (a) the absence (OT) and (b) the presence of magnetic processing (8T). In the absence of magnetic processing (OT), the polarization direction of the light against the longitudinal direction of the glass plates is horizontal...

The above results of polarized absorption spectra on glass plates support the magnetic orientation ofthe SWNT/MEHPPV composites and the shortened SWNTs in the absence and presence of NaHC03, where the composites or the SWNTs were oriented with the tube axis of the composites or the SWNTs parallel to the magnetic field (8T), suggested by the results ofthe AFM images (Figure 15.1). 

On the basis of the polarized absorption spectra (Figure 15.2), the magnetic orientation of SWNT/MEHPPV composites can also most likely be ascribed to the anisotropy in susceptibilities of SWNTs, similar to the comparison of the AFM images (Figure 15.1), as described above. 

Rosell FI, Boxer SG (2003) Polarized absorption spectra of green fluorescent protein single crystals Transition dipole moment directions. Biochemistry 42 177-183... 

In this chapter, we briefly discuss the theoretical background of polarized x-ray absorption spectroscopy (PXAS). Many of the recent applications of synchrotron radiation to polarized absorption edge structure and to EXAFS are discussed, with particular emphasis being given to the study of discrete molecular systems. We present here some indication of the potential applications of PXAS to systems of chemical and biological interest. 

Absorption Spectrum The polarized absorption spectrum of a single crystal of aspirin was measured which indicated that aspirin may be spectroscopically treated as perturbed benzoic acid.59... 

The out-of-plane orientation of chromophores can be more easily controlled in LB films as compared with the in-plane orientation. Many chromophores are known to show anisotropic orientation in the surface normal direction. The molecular structure of chromophores and their position in amphiphile molecules, the surface pressure, the subphase conditions are among those affect their out-of-plane orientation. The out-of-plane orientation has been studied by dichroic ratio at 45° incidence, absorbance ratio at normal and 45° incidence, and incident angle dependence of p-polarized absorption [3,4,27,33-41]. The evaluation of the out-of-plane orientation in LB films is given below using amphipathic porphyrin (AMP) as an example [5,10,12]. 

Figure 5 The incident (5 and polarization angle a dependence of polarized absorption. The y and z axes indicate the dipping direction and the surface normal. The transition dipole M and its xy projection makes and 0 from the z and y axes, respectively.

The angular dependence of the polarized absorption spectra of LB films containing AMP deposited at lower (20 mN m1) and higher (43 or 50 mN m 1) surface pressures was studied to determine the molecular orientation of porphyrins as schematically shown in Figure 5. No polarization angle (a) dependence was observed at normal incidence. This indicates that the projections of the transition dipole moments of the porphyrins are statistically... 

The existence of a carrier-mediated transport in nasal mucosa was first suggested by Kimura et al. [34], P-glycoprotein, organic cation transporter, dopamine transporter, and amino acid transporters have all been identified in the nasal mucosa, especially in the olfactory mucosa [31, 32, 35, 36], These transporters determine the polarized absorption and excretion of their substrates including amino acids, amines, and cations. 

Fig. 9 a Observation of intercalation of ethidium bromide into the DNA-lipid film in an aqueous solution, and polarized absorption spectra of the ethidium-intercalated stretched DNA-lipid film b in the wet state and c in the dry state. Ethidium bromide was intercalated one molecule per 10 base-pairs at 25 °C. Open, two-headed arrows show the stretching direction of the film... 

When a polarized spectrum of the film was taken in the dry state, a small dichroic ratio was observed (A L/A// = 1.3, see Fig. 9c). This is due to the slant structures of base pairs and intercalated dyes to the axis of the strands, since the DNA strands were confirmed to be aligned along the stretching direction even in the dry film (see Fig. 7c). These changes of polarized absorption spectra dependent on water moisture were reversible at least 10 times. 

The LB film of the DNA-/profiavine/2C18-glu-N complex was transferred with 44 layers (22 cycles) on one side of a glass plate (total 88 layers on both sides) and measured by polarized absorption spectra in aqueous solution (see Fig. 11a). The LB film did not swell and did not remove from the substrate... 

Fig. 11 Polarized absorption spectra of DNA /proflavine/2Ci8-glu-N LB films (88 layers) deposited by a vertical dipping method and b horizontal lifting method...

The 3.5- and 8-ntn nanoparticles show well-resolved peaks at 362 and 473 nm, respectively, as well as other features at higher energies. The 4.5-nm particles show a well-resolved peak at 400 nm and a shoulder at 450 nm. It is tempting to assume that in each case, the lowest energy absorption corresponds to the lowest allowed transition (the A exciton) in bulk M0S2. Polarization spectroscopy can be used to determine if this is the case. The lowest allowed transitions in bulk material, the A and B excitons, are polarized perpendicular to the crystallographic c axis. If the lowest allowed transition correlates to the A exciton, then it would be expected to also be a planar (xy polarized) oscillator. However, tire results of polarization studies reveal that the actual situation is more complicated. A combination of time-resolved polarized emission and one-color time-resolved polarized absorption (transient bleach) studies facillitate assignment of the polarizations of the observed nanoparticle transitions. The 3.5-nm particles are emissive and the polarization of the several of the lowest transitions may be determined... 

Figure 23-9 Polarized absorption spectra of orthorhombic crystals of cytosolic aspartate aminotransferase. The light beam passed through the crystals along the b axis with the plane of polarization parallel to the a axis (A) or the c axis (C). Left, native enzyme at pH 5.4 right, enzyme soaked with 300 mM 2-methylaspartate at pH 5.9. The band at 430 nm represents the low pH proto-nated Schiff base form of the enzyme. Upon soaking with 2-methylaspartate the coenzyme rotates 30° to form a Schiff base with this quasisubstrate. The result is a large change in the c/a polarization ratio. The 364 nm band in the complex represents the free enzyme active site in the second subunit of the dimeric enzyme.70,73 Courtesy of C. M. Metzler.

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