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

The three secondary amino nitrogens of a heteroditopic cryptand have been d erivatized with acetylpyrene to have a fluorophore-spacer-receptor configur ation. The localized monomer fluorescence intensity is reduced in this syst em due to quenching via photoinduced intramolecular electron transfer from nitrogen atoms in the receptor cryptand moiety to the fluorophores. The sys tem also exhibits a red-shifted broad structureless emission in different s olvents which is assigned to intramolecular exciplex formation. Among the d ifferent metal ions, which bind in the cryptand cavity, the local monomer e mission can be recovered to different extents in the presence of Zn(II), Co (II) and Mn(II) ions while binding of Ni(IT) or Cu(II) did not result in an y fluorescence enhancement. Presence of protons, however, facilitates intra molecular excimer formation in the free ligand. The intensity ratio of mono mer 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. (C) 2000 Published by Elsevier Sci ence B.V. All rights reserved.