<title>Optically induced azo-hydrazone tautomerism of some 2,6-dialkylphenol-based azobenzenes</title>

Abstract

The present publication is devoted to the studies of the azo- hydrazone tautomerism of some 3,5-dialkyl substituted azobenzenes. Four new 3,5-dialkyl-4-hydroxy azobenzenes containing electron acceptor SO<SUB>2</SUB> groups were synthesized and investigated in solutions, vacuum evaporated (VE) films and doped polymer films. We have observed that azo-hydrazone tautomeric equilibrium depends on the structure of the molecule and the polarity of the solvent. VE films of compounds containing a primary sulfonamide group SOP<SUB>2</SUB>NH<SUB>2</SUB> exhibit predominating azo form absorption band at about 365 nm, which decreases or disappears on UV irradiation giving rise to characteristic hydrazone absorption band at 430 nm. For the thin VE films of related derivatives containing a secondary sulfonamide group SO<SUB>2</SUB>NHC<SUB>4</SUB>H<SUB>9</SUB> we have observed predominating hydrazone form absorption band at about 430 nm or a broad band at 380 - 430 nm suggesting a tautomeric mixture. Reversible trans-cis isomerization of 3,5-dimethyl-4- hydroxy azobenzenes containing secondary sulfonamide group in the doped PMMA film was investigated.