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Fluorescence and Absorption Spectra of Phenylazopyrazolone Dyes

Peter Nikolov and Filip Fratev
Institute of Organic Chemistry , Bulgarian Academy of Sciences,
Sofia 1113
Stefan Stoyanov
Chemical Department of Sofia University,
Sofia 1024
and Oskar E. Polansky
Institut fur Strahlenchemie im Max-Planck-Institut fur Kohlenforschung,
Mülheim a. d. Ruhr
Z. Naturforsch. Ua, 191-196 (1981);

[received December 151980]

The absorption and fluorescence spectra of some arylazopyrazolone dyes have been investigated. The emission is assigned to their hydrazone form. A very good linear correlation is obtained between the a Hammett constants and the differences of the absorption nm^im* of the hydrazone form and the anion* Quantum chemical calculations indicate to a charge migration upon excitation. The electron donor substituenta cause bathochromic and hypsochromic shifts in the absorption and in the fluorescence maxima reap., while the acceptor substituents shift bathoohromically both maxima. All compounds studied except the p-N(CHs)j derivative show an anomalously large Stokes shift in nonpolar solvents.

The compounds studied are a class of widely used