Spectral shift magnitude

The intermolecular interaction described above provides information about the magnitude of spectral shifts, but it does not explain why the absorption spectra of molecular aggregates usually have either an H- or J-band. The square of transition dipole moment (in Debye2 units) is usually termed the dipole strength and is related to the intensity of the absorption band as (van Amerongen et al. 2000)... 

With a simple photodetector, a variation of 4x 10 4 in the cladding index could be detected. With some straightforward optimization, an improvement of the resolution by two orders of magnitude may be feasible. A thermally induced spectral shift of approximately 8 pm/K was observed. 

Ho et al. were able to verify the a-helical shape of the polymer by circular dichroism (CD) spectra. No structural elements were observed until the formation of the double helical DNA at which point they observed a right-handed a-helix in the polythiophene backbone. Their work demonstrates the power of fluorometric detection as they noted a seven order of magnitude increase in detection sensitivity (20 fM in 200 pi) simply through the use of fluorometric detection as opposed to UV-vis absorption. The polymer in solution has a high fluorescence yield with a maximum at 530 nm (Fig. 11a). Upon formation of the duplex the fluorescence is significantly quenched (Fig. lib), while with the addition of the complementary DNA and triplex formation, the fluorescence intensity is enhanced by a factor of 5 (Fig. 11c). The inherent sensitivity of the spectral shift even allowed distinction between DNA with only one and two mismatched bases (Fig. lOBd, e). 

Thus we see that the first moment of the spectral density multiplied by h is the reorganization energy (i.e., one half of the Stokes shift magnitude), whereas the time dependence of the first moment of p(w) corresponds to the fluorescence Stokes shift. Thus the time dependence of S t) is determined entirely by the spectral density. At high temperature [i.e., when p(w) contains frequencies less than 2kBT], S(t) becomes the classical correlation function [36] used by many previous authors [7-10], This follows from... 

Kronman et al. (1965) and Kronman and Holmes (1965) appear to be the first to have studied the effects of acid on a-lactalbumin and report that this protein, adjusted to pH values below its isoelectric point, exhibits a hypsochromic shift in its absorption spectrum between 270 and 300 nm. Spectral shifts in this region usually reflect changes in the environment of Trp and Tyr residues. The conformational change is a complex one, involving a series of steps. Because of the nature of the shift, the numbers of Trp and Tyr residues present, and the relative magnitudes of e for Trp and Tyr, Kronman and co-workers concluded that the shift results from environmental alterations for more than one of the buried Trp residues. (At the time of this study, three Trp residues were considered to be buried in bovine a-lactalbumin.) There appears to be no corresponding effect for hen egg-white lysozyme. [However, note the effect of acetic acid studied by Kato et al. (1984).]... 

Near 300 nm a spectral shift of 30 nm corresponds approximately to a change in wave number of Ai> = 3,300 cm". From Equation (1.53) this results in a p/C value change of 7 units. Since shifts of this extent are quite common on protonation, changes in dissociation constants of protonated compounds by 6-10 orders of magnitude on excitation are often observed. 

It was found that the magnitude of the shift depends, at least in part, on surface properties. With a given dye e.g., p-nitrodipheny-lamine (Fig. 17), spectral shifts of 960 and 600 A are found for this dye adsorbed on DSA-1 and SA-11, respectively. It should be pointed out that when an absorption band of a base dye borders on the visible, the shift which accompanies physisorption of the dye may be taken falsely... 

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