Chelation number of terbium dipicolinate: Effects on photoluminescence lifetime and intensity

Abstract

Time-resolved photoluminescence was studied as a function of chelation number in terbium dipicolinate. We excited the ligand (dipicolinate) with UV (250 to 330 nm) and collected the emission from the cation (terbium) in the visible region (450 to 700 nm). The luminescence of Tb(dpa)n3-2n followed a monoexponential decay, with a lifetime (0.66 to 2.0 ms) that decreased continuously as the terbium chloride concentration increased. The luminescence lifetime of Tb(dpa)+ was 0.66 ms. We measured the luminescence decay time, the peak intensity, and the total time-integrated intensity as a function of terbium chloride concentration at two dipicolinic acid concentrations and fitted the results to functions of terbium dipicolinate concentration. We used a model with rapid ligand exchange and rapid back-transfer of energy to fit the data to first order. We also present molar absorptivity spectra of complexes with different chelation numbers.