FLUORESCENCE QUENCHING OF FEW AROMATIC-AMINES BY CHLORINATED METHANES

Fluorescence quenching of few aromatic amines; aniline (AB), 1-naphthylamine (1-AN), 2-naphthylamine (2-AN), 2,3-naphthalenediamine (2,3-DAN), 9-phenanthrenamine (9-AP), 1-pyrenamine (1-APy), 2-chrysenamine (2-AC), 6-chrysenamine (6-AC), and 3-fluoranthenamine (3-AF) by dichlormethane, chloroform, and carbon tetrachloride has been studied in cyclohexane and acetonitrile. The quenching rate constants (k(q)) have been determined in both the solvents and these values are nearly independent of the solvent polarity. The values of k(q) are nearly equal to diffusion-controlled limits (k(diff)) for CHCl3 and CCl4 in both the solvents, whereas for CH2Cl2 it is three to four order of magnitude less than k(diff). For a given amine, k(q) increases with the increase in electron affinity of the quencher, whereas for a given quencher (dichloromethane) k(q) increases with the increase in singlet state energy of fluorophore. The results obtained are explained in terms of a quenching mechanism involving an intermediate donor-acceptor (DA)* complex formed between the excited aromatic amine and quencher.