Spectroscopic study of the inclusion complexes of 1-methyl-4-[4′-aminostyryl] quinolinium iodide with α,β,γ-cyclodextrins in the ground and excited states

Inclusion complexes of 1-methyl-4-[4′-aminostyryl] quinolinium iodide, (Q = +NH2)I− with α,β,γ-cyclodextrins have been investigated in the ground and excited states. The formation constant of the inclusion complexes has been determined from the spectral changes in the ground state. The higher values of the formation constant (Kf = 25,010-25,200) reflect the stability of the inclusion complexes. The increase in the formation constant in case of β-cyclodextrin (25,200) reveal that the dye was accommodated in the cavity. In the excited state, the fluorescence quantum yield (Qf) has been determined and it was 0.043 in water, 0.06 in γ-CD, 0.08 in α-CD, and 0.38 in β-CD. The increase in the fluorescence quantum yield (Qf) indicates that the dye is highly accommodated in β-CD compared to the other cavities. On the other side, at 0.01 mol dm−3, the results showed a red shifts by ∼11-13 nm in the absorption maximum in case of α,γ-CDs respectively, while in the excited states the spectra show an additional band at longer wavelength in case of γ-CD. This may be attributed to an excimer of two adjacent (Q = +NH2)I− molecules.