Photophysical properties of tris-acetylpyrene derivative of a cryptand in different environments

Abstract

The three secondary amino nitrogens of a heteroditopic cryptand have been derivatized with acetylpyrene to have a fluorophore-spacer-receptor configuration. The localized monomer fluorescence intensity is reduced in this system due to quenching via photoinduced intramolecular electron transfer from nitrogen atoms in the receptor cryptand moiety to the fluorophores. The system also exhibits a red-shifted broad structureless emission in different solvents which is assigned to intramolecular exciplex formation. Among the different metal ions, which bind in the cryptand cavity, the local monomer emission can be recovered to different extents in the presence of Zn(II), Co(II) and Mn(II) ions while binding of Ni(II) or Cu(II) did not result in any fluorescence enhancement. Presence of protons, however, facilitates intramolecular excimer formation in the free ligand. The intensity ratio of monomer and excimer emission is found to be a function of proton concentration. The system is thus a rare one exhibiting monomeric, excimeric and exciplex emissions depending on the environment.