Abstract
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 σ Hammett constants and the differences of the absorption maxima of the hydrazone form and the anion. Quantum chemical calculations indicate to a charge migration upon excitation.
The electron donor substituents cause bathochromic and hypsochromic shifts in the absorption and in the fluorescence maxima resp., while the acceptor substituents shift bathochromically both maxima. All compounds studied except the p-N(CH3)2 derivative show an anomalously large Stokes shift in nonpolar solvents.
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