Abstract:

The introduction of chromophoric azo group into calixarene was of great value for the development of functional calixarenes, and the azo-coupled calixarene usually showed large UV-Vis band shifts when base was added. Eight azocalixarene compounds were synthesized by diazo-coupling reaction. These compounds were characterized by IR, ¹H NMR, ESI-MS and elemental analysis. The effect of varying pH values upon the absorption ability of both 5,11,17,23-tetra[(2-benzothiazole)azo]-25,26,27,28-tetrahydroxycalixarene and 5,17-di[(1-naphthyl)azo]-25,26,27,28-tetrahydroxycalixarene was tested to study the azo-quinoid tautomerizm phenomena. Observed result exhibit that with the increasing of pH, the proportion of quinoid tautomer in azo-quinoid tautomerizm equilibrium is rised. Unexpectedly an conjugated system may be formed in the condition of pH=-1 for 5,17-di[(1-naphthyl)-azo]-25,26,27,28-tetrahydroxycalixarene, of which the UV absorption spectra show substantial bathochromic shifts(Δλ=477—545 nm).

Key words: Azocalixarene, Diazo-coupling reaction, Acidity effect, Azo-quinoid tautomerizm