Chromophores substituents

Phosphazene polymers are inherently good electrical insulators unless side-group stmctures allow ionic conduction in the presence of salts. This insulating property forms the basis for appHcations as wire and cable jackets and coatings. Polyphosphazenes also exhibit excellent visible and uv radiation transparency when chromophoric substituents are absent. 

The coloration efficiency of photochromic spirocompounds may be enhanced by careful selection of additional chromophoric substituents. Tomasulo et al. reported amplification of coloration efficiency of photochromic oxazines using a bichromo-phoric approach [25],... 

R = a functionally modified carboxy-group, an optionally substituted Ph group or an optionally substituted 5-membered heterocyclic ring R = H, an alkyl group or an optionally subst. Ph group, = 0 or 1 and or 5 may contain non-chromophoric substituents... 

Table 7.10 demonstrates the effect of acidity or basicity of the solution on such a chromophoric substituent group. In the case of benzoic acid, the primary and secondary bands are shifted substantially from those noted for benzene. However, the magnitudes of the shifts are somewhat smaller in the case of benzoate ion, the conjugate base of benzoic acid. The intensities of the peaks are lower than for benzoic acid, as well. We expect electron transfer of the sort just shown to be less likely when the functional group already bears a negative charge. 

B Conformational and association equilibria of a modified cyclodextrin with a chromophoric substituent in the presence and absence of an additional achiral guest and their manifestation in the CD spectra... 

Although the Cotton effects of a-amino acids can be measured directly with up-to-date ORD/CD equipment, more often it is advantageous to form chromophoric derivatives or complexes whose chiroptical properties reflect the absolute configuration of the a-carbon atom. This is especially important when adequate instrumentation is not available or chromophoric substituents other than COOH or NH2 are present. For instance, in the case of aromatic amino acids, more complex chirospectral patterns have to be considered which might prevent the unequivocal assignment of absolute stereochemistry. Also, minor optically active impurities might interfere with spectral data in the 200-250-nm area. 

The chromophoric derivatives (1) have a chromophore that is optically inactive by nature but becomes optically active in the vicinity of the asymmetric a-carbon atom (2) absorb in the near-uv or visible spectral range (above 300 nm, where the aromatic and other chromophoric substituents are transparent) and (3) preferably have a rather high Kuhn s dissymmetry factor... 

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