LUMINESCENCE PROPERTIES OF TERBIUM(III) COMPLEXES WITH 4-SUBSTITUTED DIPICOLINIC ACID ANALOGS

The spectral properties of Tb(III) complexes with a series of 4-substi tuted analogues of dipicolinic acid (2,6 pyridinedicarboxylic acid) we re compared. Analogues in which the 4-substituent was -H, -OH, -Cl, -B r, -NH2, or -NHAc all sensitized emission from bound terbium ions when excited with ultraviolet light. Molar extinction coefficients of the complexes at the wavelengths of maximum absorbance were in the range ( 2.2 x 10(3) to 8.3 x 10(3)) M(-1) cm(-1) with magnitudes in the follow ing order: NHAc > NH2 > OH > H > Br > Cl. When excitation spectra of T b(III) complexes were measured under identical conditions for each lig and, the maximum Tb(mj emission intensities were in the following orde r: NH2 > NHAc > OH > K > Cl similar to Br. Measurements of Tb(III) emi ssion decay kinetics revealed lifetimes in the range 1.0-2.0 ms. Relat ive quantum yields for energy transfer were ordered as follows: NH2 > OH > NHAc > Cl > H similar to Br. Energy transfer efficiency was not e nhanced when Br was substituted for Cl at the 4-position, consistent w ith energy transfer from excited singlet, rather than triplet states. The efficient sensitization of Tb(III) emission by the analogues with nitrogen at the 4-position suggests that this class of compounds will be most useful for developing millisecond luminescence probes for bioa nalytical studies.