Molecular orientation of oxacyanine dye in an LB film determined by secondharmonic generation and polarized absorption techniques

The molecular orientation of an oxacyanine dye (DOOC) in an LB film has bee n determined based on the second harmonic generation (SHG) using a fs-pulse d Ti-sapphire laser and the polarization absorption spectrometry. Both pola rization and wavelength dependence of SHG varied with surface concentration of the dye. The dye was either in a monomer, a dimer or a J-aggregate form depending on the surface concentration. The tilt angle to the surface norm al was 34 degrees for the monomer, 26-29 degrees for the dimer and 16-23 de grees for the J-aggregate. The J-aggregate stayed more flat on surface and showed larger SHG intensity than the monomer did. (C) 1999 Elsevier Science S.A. All rights reserved.