Synthesis, Optical Characteristics and Complex Formation of Molecular Receptors Based on 1,8-Naphthalimide Derivatives in Solution and in Composition of Hybrid Tin Dioxide Nanoparticles

In the present work the synthesis of N-alkyl- and N-phenyl-1,8-naphthalimides containing dithiacrown ether, carboxyl group or both of these substituents has been developed. Molecular receptor 4-methoxy-N-benzodithiacrown-1,8-naphthalimide was synthesized from anhydride of 4-nitro-1,8-naphthalene dicarboxylic acid by acylation of crown-containing aniline and the replacement of nitro group onto methoxy one. Carboxylic derivatives of 1,8-naphthalimide with or without thiacrown ether moiety were prepared and the method of their covalent attachment to the SnO2 surface has been proposed. Molecular receptor 4-methoxy-N-benzodithiacrown-1,8-naphthalimide demonstrates selectivity towards Hg2+ and Pb2+ cations in acetonintrile solution and towards Hg2+ in aqueous media. Due to its structure this receptor shows low fluorescence intensity in the free state and substantial increase of fluorescence in the presence of Hg2+ and Pb2+ is observed. This phenomenon is explained by the fact that an efficient photoinduced electron transfer takes place between fluorophore and receptor parts of the molecule in the absence of metal ions, resulting in fluorescence quenching. Electron transfer process is blocked in the presence of metal ions because the lone pair of electrons originally involved in the electron transfer process is engaged in metal ion binding. As a result the fluorescence enhancement is observed upon complexation with metal ions. 1,8-Naphthalimide derivatives in the composition of hybrid SnO2 sol demonstrate optical characteristics similar to those of molecular fluorophores. However, the binding of metal ions by hybrid nanoreceptor was not observed. It should be due to effective interaction of crown-containing molecule with SnO2 surface.