Influence of cyclodextrin complexation on the emission of thioflavin T and its off-on control

Abstract

The effect of cyclodextrin (CD) complexation on the emission of thioflavin T is studied at room temperature. Formation of 2:1 (TFT⁺:γ-CD) inclusion complex at lower concentration and 2:2 inclusion complex at higher concentration of γ-CD is observed. The formation of 2:1 inclusion complex caused a decrease in the emission intensity and an increase in the emission intensity with a red shift in the emission band due to the formation of emittive dimer by the 2:2 inclusion complex. The observed dimer emission in the presence of γ-CD underwent "off-on" switching in the presence of an acid. In the acid medium, the TFT⁺ molecule underwent protonation and the protonated dye molecule (TFTH²⁺) cannot form dimer in the cavity of γ-CD because of the electrostatic repulsion. 3D emission spectral studies were carried out for the γ-CD inclusion complex of TFT⁺. Enhancement in the emission intensity of TFT⁺ was noticed in the presence of β-CD and hydroxypropyl–β-CD (HPCD). The dimer emission of TFT⁺ was not observed in the presence of β-CD and HPCD. The stoichiometries of the inclusion complexes were found to be 1:1 and 1:2 (TFT⁺:β-CD) in the case of β-CD and 1:1 in the case of HPCD. Formation constants were calculated for the inclusion complexes of TFT⁺ with different CDs.