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Figure 4. Correlation between molar absorptivity of IA Dye – 12-tungstogallate

measured at analytical wavelength (corresponding to the maximum in the difference

spectrum) and molar absorptivity of the dye.

Dye: 1 – Chompyrazole-1; 2 – Malachite Green; 3 – Crystall Violet; 4 – Rhodamine 6G; 5 –

Astra Phloxine

The second important factor reflects the influence of the structure of dyes and

their relative position in the molecular structure of IA on the steric structure of the
aggregate formed. According to the exciton theory, the initial intensity of the dye band
is redistributed between the two new bands, and the obtained sum of intensities is
approximately equal to the initial intensity. Extent of redistribution between new bands
depends on the angle between the chromophores. As can be seen from the spectra
presented by us, the most favorable is the redistribution in the case of rhodamine and
especially polymethine dyes. For Astra Phloxine, both new bands are approximately
equal in intensity while for triphenylmethane dyes the blue-shifted band is substantially
more intense than the red-shifted. For triphenylmethane dyes, the molar absorptivity is
nearly 2.5 times smaller than for polymethine dyes, while other things being equal, the
molar absorptivity for rhodamine dyes is about 1.5 times smaller.

Quantitatively, the second criterion proposed is the ratio of the molar absorptivity

of the ion associate calculated at analytical wavelength (with considering the dye
absorbance) and molar absorptivity of the dye calculated at absorption maximum.

We cannot evaluate molar absorptivity coefficient for the IA if the measurements

are made in the excess of the anion. In these conditions, only molar absorptivity for the
aggregated dye can be obtained. As it is well seen from the Table 1, value for this
constant practically does not depend on the charge of HPA and composition of IA. It

40000

60000

80000

100000

120000

140000

40000

80000

120000

160000

200000

Dye

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