Effect of β-cyclodextrin on intramolecular charge-transfer emission of 4-aminophthalimide

Abstract

Steady state and time-resolved studies on the fluorescence of 4-aminophthalimide (AP) in aqueous β-cyclodextrin (CD) solutions are reported. A blue shift of the fluorescence maximum, enhancement of the fluorescence quantum yield and increase in the lifetime of the emitting intramolecular charge-transfer state are observed on addition of CD to an aqueous solution of AP. It is suggested that the elimination of water molecules from the surrounding of the fluorescent probe, as a result of encapsulation, leads to the changes in the photophysical properties. The formation constant of the complex is estimated from the pre-exponential factors of the biexponential decay of the fluorescence and is found to agree reasonably well with that obtained from fluorescence intensity measurements.