Solvatochromic Properties of Some 6,7-Dihydroxybenzopyryllium Perchlorate Derivatives

Abstract

The creation of new reagents based on benzopyrylium derivatives with improved che­mical-analytical characteristics is of interest because their preparative synthesis is relatively simple and consists in the condensation of triatomic phenols with β-dicarbonyl compounds. Benzopyryllium derivatives are reactive compounds and are able to redox reactions, complexes formation with polyvalent metal ions, and are also prone to acid-base transformations in solutions. It should be noted separately that hydroxyderivatives of ben­zopyrylium during complex formation can turn into anhydro bases with a quinoid structure, which leads to a significant bathochromic shift of the absorption band and an increase in the contrast of analytical reactions. The current work is devoted to the study of solvatochromic pro­perties of a number of 6,7-dihydroxybenzopyrylium perchlorate derivatives: 6,7-dihyd­roxy-2,4-dimethylbenzopyrylium, 6,7-dihyd­roxy-2-phenyl-4-methylbenzopyrylium and 6,7-di­hyd­roxy-2,4 -diphenylbenzopyrylium. The presented work is a continuation of research on synthesis, acid-base and complexation of 6,7-­dihyd­roxybenzopyrylium derivatives. The influence of the nature of organic solvents was stu­died using the example of methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, n-pentanol, iso-pentanol, n-hexanol, n-heptanol, n-nonanol, decanol, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, acetonitrile, butyl acetate, toluene, and chloroform. It is shown that when a polar solvent is replaced by a less polar one, a bathochromic shift of the maximum of the absorption band of 6,7-dihydroxybenzopyrylium derivatives is observed, which corresponds to the n→π* electronic transition. It was noted that there is a satisfactory correlation (R = 0.795–0.993) between the position of the maximum absorption of the dye and the values of the Hansen parameter, Kamlet – Taft, donor and acceptor number according to Gutman.