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309 Figure 9. Shematic representations for possible structures of a bound monomer (a), a bound racemic aggregate (b), and a bound enantiomeric aggregate (c). The ligands in Cop2+ are represented by two ovals around a small open circle. The shaded and unshaded parts denote the portion of a ligand directed downward and upward from the paper, respectively. below the possible structures of the bound states on the basis of the calculations.For a bound monomer state, the experimental values of pI and pIr (+1.10 and -0.40 in Table I, respectively) were reproduced from the curves in Figure 8, if a and @(E) were chosen as 0' and 0.4, respectively. Under this conformation, it was possible for each of the naphthalene rings in Cop2+ to penetrate between the two neighboring styrenesulfonate residues. Accordingly the bound chelate would be stabilized due to the van der Waals interactions between the naphthalene of COP,+ and the benzene rings of PSS-. The hydrophobicity of PSS-as seen here was already noted by other investigator^.'^ For a racemic aggregate state, the experimental pI and. pII (+0.43 and +O. 10, respectively) corresponded to the theoretical values at a = 35O and @(E) = 0.4. If (+)-Cop2+ and (-)-Cop,+ (13) Tondre, C.; Kale, K. M.; Zana, R. Eur. Polymn. J. 1978, 14, 139.were placed alternatively along the Y axis under this conformation as shown in Figure 9b, the two facing ligands belonging to the neighboring chelates stacked preferably with each other. As a result, the racemic aggregate established a rigid rodlike structure. This explains why the racemic mixture attained a stereoregular racemic aggregate as the most thermodynamically stable state.For an enantiomeric aggregate state, the experimental pI and prI (+0.21 and +0.25, respectively) were reproduced by choosing a = 45' and @(E) = 0.4. When (+)-Cop,+ ions were placed along the Y axis with a = 45' in a sequence, no notable stacking appeared between the neighboring ligands. If, however, one chelate was placed at a = 45' and the other at a = -45' instead, the two ligands in the neighboring chelates stacked to a certain degree (Figure 9c).I4 The relative orientations of the stacking ligands were not so favored that the enantiomeric aggregate was much looser than the racemic aggregate.The stopped-flow experiments revealed the presence of an intermediate state during the course of formation of a racemic aggregate. The intermediate aggregate was formed about 4 ms after mixing when the initial rapid increase of absorbance was completed. It is suspected that, in such an intermediate state, the (+) and (-) isomers take a random distribution on the PSSchain. Accordingly, the sequence could not attain a close stacking as a whole. If this was the case, the succeeding slow step in the time range of 1-lo2 s might represent the process that the bound chelates rearranged on each polymer chain until the alternative sequence of (-)-Cop2+ and (+)-Cop2+ was realized. At that stage, the loosely bound aggregate changed into a rigid stereoregular racemic aggregate. This mechanism ...

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We study the nonlinear propagation of femtosecond pulses in the anomalous dispersion region of microstructured fibers, where soliton fission mechanisms play an important role. The experiment shows that the output spectrum contains, besides the infrared supercontinuum, a narrow-band 430-nm peak, carrying about one fourth of the input energy. By combining simulation and experiments, we explore the generation mechanism of the visible peak and describe its properties. The simulation demonstrates that the blue peak is generated only when the input pulse is so strongly compressed that the short-wavelength tail of the spectrum includes the wavelength predicted for the dispersive wave. In agreement with simulation, intensity-autocorrelation measurements show that the duration of the blue pulse is in the picosecond time range, and that, by increasing the input intensity, satellite pulses of lower intensity are generated.