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

Abstract

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 Pb(2+) 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 (K(ass)) were calculated using the equation, 1/K(ass) [L(o)] = (1 -nP)(n)(1 -m)(m)/P with linear best fit of plots depending on 1/[L(o)] where P = P(C)/[1 + (m - 1)P(C)] and P(C) is the mole fraction of n/m ratio of the complexed ligand. The association constants of cations, K(ass), 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.