Structure characterization of new cyanine dye Langmuir-Blodgett multilayers by polarized UV-vis spectroscopy

Abstract

We investigated on cyanine dye (HQ) in Langmuir and Langmuir-Blodgett (LB) films by surface pressure-area (&#960;-A) isotherms, UV-visible and polarized UV-visible spectra as well as small angle x-ray diffraction (SAXD) measurement. It is found from the isotherms that there is a <i>critical point </i>on Langmuir films near the area 0.8nm²/molecule for HQ LB films with and without Cd²⁺ ions respectively and suggested that the facts should result from the phase transition due to the change of molecular tilt angle on surface of sub-phase. UV-visible spectra indicated a uniform film transfer. The orientation angle of HQ molecular chromophore in LB films was measured by polarized UV-visible absorption spectra, and the result showed that the angle with respect to the substrate surface was 65 and 59 degree without and with Cd²⁺ ions respectively, which are agreement with those obtained from the surface pressure-area isotherm. It is suggested that the arrangements of the HQ molecule in LB films incorporating Cd²⁺ions was more compact than those without Cd²⁺.