Analysis of counter ions of cyanine dye in Langmuir-Blodgett films by PIXE

Langmuir-Blodgett (LB) films of 1-methyl-1'-octadecylquinocyanine bromide, iodide and perchlorate were prepared from subphases containing NaClO4, KBr and/or KI. Each sample consists of an arachidic cadmium layer and about 100 cyanine dye layers on a Si substrate. Anions incorporated into the film as counter ions from the subphase were analyzed by particle induced X-ray emi ssion (PIXE) using a 2.5 MeV He2+ beam. It was found that the dissociation of the cationic dye molecule in the monolayer at the air/water interface le ads to the substitution of counter anions of the dye molecules, and the sub sequent incorporation of the counter anions in the LB films. Some of the di ssociation constants of cyanine halide dyes were estimated. (C) 2000 Elsevi er Science B.V. All rights reserved.