Azocalixarenes.7: Synthesis and study of the absorption properties of novel mono-azo substituted chromogenic calix[4]arenes

Eight new mono-azo substituted chromogenic calix[4]arenes (1-8) were synthesized by diazo-coupling re- actions in which 25,26,27-tribenzoyloxy-28-hydroxy-5,11,17-tri-(tert -butyl)calix[4]arene and diazonium salts (2-, 3-, and 4-nitroaniline; 4-phenyl azoaniline; 3- and 4-chloroaniline; or 2- and 4-methylaniline) formed the corresponding mono-azo substituted derivatives in high yields. The mono-azo substituted calix[4]arenes were characterized by UV-Vis, FT-IR, and 1 H-NMR spectroscopic techniques. Elemental analysis was also carried out. In addition, the effects of varying pH levels and solvents upon the absorption ability of azo- calix[4]arenes substituted with electron-donating and electron-withdrawing groups at their o-, m-, and p- positions were studied. The results proved that the absorption maxima of the prepared compounds showed large bathochromic effects in comparison with analog compounds containing aromatic amine residue. Fur- thermore, concentration effects on the visible absorption maxima of the azocalix[4]arene compounds studied were also reported.