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 reactions 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 H-1-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. Furthermore, concentration effects on the visible absorption maxima of the azocalix[4]arene compounds studied were also reported.