Effect of α- and β-cyclodextrins on S-triazine derivatives: spectral and molecular modelling studies

Cyclodextrins (CDs, α-CD and β-CD) effects on three S-triazine derivatives (1A, 1B and 1C) were investigated by absorption, fluorescence and molecular modelling studies. A regular red and blue shift observed in acidic buffer medium suggests intramolecular proton transfer (IPT) present in these molecules. The longer wavelength emission intensity dramatically increased with the β-CD concentrations while in α-CD solution, the shorter wavelength emission intensity is increased. Considering size and shape of the CDs and guest molecules, S-triazine molecules are partially encapsulated within the CD cavity. Semiempirical quantum mechanical calculations have also been carried out to ascertain the mode of inclusion process. These results indicate that amino form is energetically favourable than imino form, which is consistent with experimental results.