New 4-amino-N-alkylphthalimides as fluorescence probes for β-cyclodextrin inclusion complexes and hydrophobic microdomains of amphiphilic systems

The synthesis and photophysical behaviour of a series of 4-amino-N-alkylphthalimides have been described. The complexation between β-cyclodextrin and the different phthalimides has been studied by steady-state fluorescence. The association constant K depends strongly on the hydrophobicity of the alkyl substituent, and the K values vary between 115 M−1 and 19,000 M−1. The studied compounds have been used as fluorescent probes to determine the first and second association constants of surfactants with β-cyclodextrin from competitive binding data. The results are compared with those given by other authors, and limitations of the method are discussed. 4-Amino-N-tert-butylphthalimide is also used as a sensor for following micellar aggregation process of surfactants and autoassociation of hydrophobically modified polymers. Values of critical micellar concentration (cmc) and critical aggregation concentration (cac) are determined, and comparison is made with pyrene.