CHARGE-TRANSFER LIKE COMPLEXES OF ORGANIC-DYES ADSORBED AT COLLOIDAL SILVER STUDIED BY CYCLIC VOLTAMMETRY, UV-VIS AND SERS SPECTROSCOPY

After adding cationic dyes like oxazine 170, malachite green, and crys tal violet to a solution of colloidal silver sometimes an absorption b and appears at wavelengths > 750 nm which is neither caused by the mon omeric dye nor by a coagulation of the colloid. Based on electrochemic al measurements this new absorption band is assigned to a chinhydron-l ike adsorption geometry of the dye. Usually this band is only observed at low concentration of the dye, whereas al higher concentration the formation of H-aggregates occurs. There seems to be a relationship bet ween the intensity of this band and the SERS activity.