Cryptand-based fluorescent signaling systems: high enhancement with transition, inner-transition as well as heavy main-group metal ions

Two laterally non-symmetric cryptands have been selectively derivatized with anthryl groups to have fluorescent signaling systems in the format, “receptor–spacer–fluorophore”. In absence of a metal ion, no fluorescence is observed upon excitation of the anthryl moiety due to an efficient photoinduced electron transfer (PET). However, in the presence of transition metal ions such as Mn(II), Co(II), Ni(II), Cu(II), and Zn(II); heavy metal ions such as Pb(II), Hg(II), Tl(I), and Ag(I); or lanthanide ions such as Eu(III), Tb(III), Nd(III), Er(III), and Dy(III), the PET is blocked and the fluorescence could be recovered to different extents. The quantum yields of fluorescence enhancement depend upon the nature of the metal ion as well as the cryptand receptor.