Study of the adsorptive behavior of water-soluble dye molecules (rhodamine6G) at the air-water interface using confocal fluorescence microscope

A confocal fluorescence microscope was applied to directly study the charac teristic behaviors of adsorbed molecules at the air-water interface for a w ater-soluble chromophore, rhodamine 6G (R6G), in its extremely low-concentr ation region (below 10(-10) M). Significant photon bursts were observed onl y from the surface, and their width, height, and frequency were found to de pend on the bulk concentration, suggesting the inhomogeneous distribution o f R6G molecules at the air-water interface. This property of the adsorbed m olecules is different from that of the bulk one. The influence of the ionic strength on photon bursts from the interface was investigated. It was foun d that the addition of NaCl to the R6G solution caused a decrease of the fl uorescence signal. A change in the size of the aggregate and in the fluores cence quantum yield of the adsorbed molecules was suggested to be responsib le for this experimental result. (C) 2001 Elsevier Science B.V. All rights reserved.