FLUORESCENCE QUENCHING OF 1-CYANONAPHTHALENE BY IODIDE AND THIOCYANIDE ANIONS IN POLAR-SOLVENT

Fluorescence quenching of 1-cyanonaphthalene (1-CNN) by iodide and thi ocyanide anions in ethanol, acetonitrile, water and in water solution of 0.02 M beta-cyclodextrin has been investigated. The mechanism of th e fluorescence quenching of 1-CNN by inorganic anions is the electron transfer from the anion to the excited 1-CNN molecule, confirmed previ ously by nanosecond transient absorption measurements. The Stern-Volme r plots exhibit the positive curvatures, indicating relatively strong diffusion Limitation of the quenching process. Diffusion coefficients and encounter radii for the investigated systems were calculated from the nonlinear Stern-Volmer dependencies using the procedure by Stevens . It has been found that mutual diffusion coefficients are in agreemen t with those taken from other published sources. Both the diffusion co efficients and encounter radii estimated for the systems containing 1- CNN complexed with beta-cyclodextrin are similar to those in ethanol, which indicates similarity of cyclodextrin cavities to ethanol.