Charge transfer bands in the luminescence excitation spectra of isomeric pyridinedicarboxylic salts of europium

The ligand-cation charge transfer band was observed in the region of 360-400 nm of the luminescence excitation spectrum of europium salt of 3,4-pyridinediearboxylic acid but was absent in the spectra of europium 2,6- and 2,3-pyridinedicarboxylic salts. It was due to higher efficiency of the energy transfer through the charge transfer state conditioned by increased polarizability of the ligand of the former compound. Energy transfer through the excited ligand-lanthanide charge transfer state may explain the effect of the quenching of luminescence by the redox-sensitive lanthanide ions. (C) 2002 Elsevier Science B.V. All rights reserved.