Attenuated total reflection properties and structures in squarylium LB films

The attenuated total reflection (ATR) properties, as a function of the incident angle of the laser beam, were investigated for squarylium (SQ) Langmuir-Blodgett (LB) films on thin Ag layers. Photosensitive SQ dyes exhibit strong absorption in the visible. The ATR curves are strongly dependent on the number of LB monolayers; the resonant angles at the dips increase with increasing number of monolayers. The complex dielectric constants of the LB films (uniaxial anisotropic dielectrics) were determined by fitting the theoretical ATR curves to the experimental curves. The ATR properties suggest that the tilt angles of the long axes of the chromophores in the SQ molecules are about 10 degrees from the LB film plane for two layers and about 30 degrees for more than four layers, Since H aggregation of SQ molecules in LB films is generated on annealing and the absorption spectra change, the ATR properties were also investigated for annealed SQ LB films. The properties are of interest for optical applications.