Photophysical and Photoprototropic Characteristics of 2-Aminobenzothiazole in β-Cyclodextrin Medium

The formation of stable inclusion complexes between neutral and monocationic species of 2-aminobenzothiazole (2ABT) with β-CDx is observed with significant enhancement in absorbance and fluorescence intensity. The stoichiometry of the 2ABT and 2ABTH^⊕ with β-CDx is found to be 1:1 at pH 6.8 and 1.1. Their binding constant values for neutral and monocationic species are found to be 1239.3 and 1259.2 M^-1, respectively. Lifetime analysis, FT-IR spectral and SEM image analysis strongly supports the formation of the inclusion complex between 2ABT and β-CDx. Photoprototropic study shows that there is no remarkable difference in the pK _a and pK _a* in aqueous and β-CDx media, which is rules out the formation of the inclusion complex with -NH₂ group of 2ABT inside the cavity of β-CDx i.e., the -NH₂ group of 2ABT is in aqueous environment. Based on stoichiometry, binding constant and acidity constant values, the structure of the 1:1 complex is proposed.