Association constants of dibenzo[3n + 2]crown-n ethers using steady-state fluorescence spectroscopy

The steady-state fluorescence spectra of cation complexes of fluorophore macrocyclic ethers have been studied for the estimation of 1:1 association constants, and perchlorate salts of Li+, Na+, K+ Rb+ and Pb2+ complexing with dibenzo[23]crown-9, dibenzo[26]crown-10, and sym-dibenzo[26]crown-10, were investigated. The fluorescence emission maximum of the free and the various ligand/cation mixtures of complexed crown ethers were measured at room temperature in AN. The concentrations of chromophore crown ether were obtained from nonlinear calibration plots. The 1:1 stoichiometry of association constants (Kass) were calculated using the equation, 1/Kass [Lo] = (1 − nP)n(1 − m)m/P with linear best fit of plots depending on 1/[Lo] where P = PC/[1 + (m − 1)PC] and PC is the mole fraction of n/m ratio of the complexed ligand. The association constants of cations, Kass, displayed the cation selectivities depending on the cation radii and the macrocyclic ether size, and Pb+ was found to give the strongest association with such crown ethers.