Squaryium Dyes Based on 2,6-Di-tert-butylselenopyrylium or Telluropyrylium Nuclei

The condensation of 2,6-di-tert-butyl-4-methylselenopyrylium and -telluropyrylium salts with squaric acid gives squarylium dyes with absorption maxima at 847 and 910 nm, respectively, in dichloromethane. The condensation of a 2,6-di-tert-butyl-4-ethylselenopyrylium salt with squaric acid gives the corresponding dimethyl-substituted squarylium dye with an absorption maximum at 906 nm in dichloromethane. Electrochemical reduction and oxidation potentials of these dyes are compared to those of the corresponding squalium dyes based on pyrylium and thiopyrylium nuclei