Effect of Solvents and pH on β-Cyclodextrin Inclusion Complexation of 2,4-Dihydroxyazobenzene and 4-Hydroxyazobenzene

Abstract

The spectral characteristics of 2,4-dihydroxyazobenzene (DHAB, sudan orange G) and 4-hydroxyazobenzene (HAB) have been studied in various solvents, different hydrogen ion and β-cyclodextrin (β-CD) concentrations, and are compared with azobenzene (AB). The inclusion complexes of the above molecules with β-CD were analyzed by UV-vis spectrometry, flourometry, FT-IR, 1H NMR, SEM and DFT methods. The solvent study shows that only the azo form is present in DHAB and HAB molecules. The unusually large red shift observed in acidic solutions indicates both molecules exhibit azo-hydrazo tautomerization. In the β-CD solutions, the increase in fluorescence intensity and large bathochromic shift in the S1 state indicates that DHAB and HAB form 2:2 inclusion complexes, whereas AB forms a 1:1 inclusion complex.