New flexible molecular probes bearing dansyl and TEMPO moieties for host–guest interactions in solution and gels

Abstract

A series of nine dual molecular probes containing dansyl and TEMPO groups with fluorescent and paramagnetic properties, respectively, linked by linear alkyl chains were synthesized and characterized. The series of probes bearing only the dansyl moiety was also obtained. The photophysical properties of the probes were investigated in aqueous solution and the results evidenced the quenching effect of the nitroxide group on the fluorescence quantum yield of the dansyl moiety. Host–guest interactions of these dual molecular probes with β-cyclodextrin were investigated simultaneously by electron paramagnetic resonance (EPR) and fluorescence spectroscopies. The analysis of both EPR and fluorescence data evidenced the formation of complexes with preferential inclusion of the dansyl group in the cyclodextrin cavity and 1 : 1 stoichiometry. The association constants for the inclusion complexes were of the 10² M⁻¹ order of magnitude. Diffusion experiments of the probes in natural and functionalised alginate gels bearing adamantane and/or cyclodextrin units have shown the suitability of these compounds to describe interactions in complex and non-uniform systems in which host–guest interactions play an important role.