Efficient visible light sensitisation of water-soluble near-infrared luminescent lanthanide complexes

Fluorexon (4',5'-bis[N,N-bis(carboxymethyl)aminomethyl]fluorescein) forms s table, water-soluble complexes with lanthanide ions. The complexes with neo dymium(III), erbium(III) and ytterbium(III) display sensitised near-infrare d lanthanide luminescence upon excitation of the fluorexon with visible lig ht. The photosensitisation efficiency is very high (0.5-1.0) as a result of lanthanide-enhanced intersystem crossing in the sensitising chromophore an d rapid intracomplex energy transfer. The overall luminescence quantum yiel ds, however, are low (2 x 10(-4)-5 x 10(-3)) due to nonradiative deactivati on of the excited lanthanide ion.