4-Aminophthalimide derivatives as environment-sensitive probes

The potential of 4-aminophthalimide (AP) and its derivatives as fluorescenc e probes for organized media is highlighted. The fluorescence response of A P, as measured from the position of the fluorescence maximum, fluorescence intensity and lifetime, is highly sensitive to the polarity of the medium. The sensitivity of the fluorescence parameters is further enhanced due to t he involvement of the emitting intramolecular charge transfer state in hydr ogen bonding interaction with the solvent molecules containing hydroxyl gro ups. It is shown that the microheterogeneous environments of organized medi a such as cyclodextrins and micelles can be very conveniently monitored usi ng this probe. The results of the investigations carried out employing AP a nd its derivatives as fluorescence probe molecules in these media clearly s uggest that a combination of the hydrophobic interaction with the host medi a and hydrogen bonding interaction with the solvent molecules determine the location of the fluorophore, which in all cases is found to be the interfa cial region separating the nonpolar core of the micelle or the cyclodextrin cavity and the polar aqueous environment. Guidelines for the design of pro bes of this class of systems for the nonpolar core region of the micelles a re provided and possible ways to increase the sensitivity of the fluorescen ce response of the systems are suggested.