The technique of optical second-harmonic generation (SHG) interference was applied to evaluate the nonlinear polarization vector of a monolayer assembly at the air/water interface. Coherent interference patterns of second-harmonic (SH) waves from a sample monolayer and a reference SHG-active material were clearly observed. Interference patterns were compared with three SHG-active amphiphilic dyes: ruthenium complex, stilbazole and hemicyanine dyes. The ruthenium complex and the hemicyanine dyes afforded almost identical interference patterns of SH waves, indicating the same sign of the nonlinear polarization vector in the monolayers with respect to the water surface. In spite of the fact that the stilbazole and the hemicyanine dyes have the same SHG-active moiety, an almost 180° phase shift of the interference patterns was observed. This result shows that the nonlinear polarization vector of the stilbazole monolayer is oppositely directed to that of the hemicyanine monolayer.
All Science Journal Classification (ASJC) codes
- Analytical Chemistry