EFFECT OF HYDROXYL SUBSTITUTION IN SQUARAINE DYES ON THEIR AGGREGATION IN LANGMUIR-BLODGETT-FILMS

In this paper we study the effect of hydroxyl substituents at the benz ene ring of the squaraine dye chromophore and different alkyl substitu ents at the N atom on the aggregation state of dyes in Langmuir-Blodge tt (LB) films. Squaraine dyes were used as follows: dye I, minophenyl) -4-(4-dipropyl-iminocyclohexa-2,5-dieny lidene)-3-oxocyclobut-1-enolat e]; dye II, clohexa-2,5-dienylidene)-3-oxocyclobut-1-enolate]; and dye III, [2-(2-hydroxyl-4-ethyl, stearylaminophenyl)-4-(2-hydroxyl-4-ethy l, clohexa-2,5-dienylidene)-3-oxocyclobut-1-enolate]. Surface pressure -area isotherm studies showed that the molecules of squaraine dyes I, II and III may be residing vertically along its short axis on the wate r surface with an area of 0.75 nm(2), standing at the water surface on the faces of smallest area of 0.27 nm(2) and residing vertically alon g its short axis on the water surface with an area of 0.72 nm(2) respe ctively. Stable LB films can be obtained by mixing dye with arachidic acid (C-20) The aggregation of the squaraine dyes in these mixed monol ayers were studied by reflection spectra of surface and that of their LB films by absorption spectroscopy. Spectral data showed that the agg regation states of dyes I, II and III in mixed monolayers and LB films not only are different from their solution absorption spectra but als o are different from each other.