The formation and structure of aggregates in hemicyanine monolayers

Abstract

Absorption spectra of a hemicyanine monolayer on a sodium sulfate subphase were recorded as a function of surface pressure. Upon compression, the intensity of the monomer band is reduced and two new bands are observed. The results from principal factor analysis of the spectra and the clear isosbestic points indicate that the two bands are due to exciton splitting from an aggregate structure with two molecules per unit cell. By comparison with spectra obtained previously, the influence of counterions and the dilution of the dye monolayer on the formation and structure of the aggregates is investigated. The addition of sulfate counterions to the subphase raises the threshold surface concentrat..