Second-order nonlinear optical effects in stacked assemblies of ultrathin polymer films with amphiphilic ruthenium complex

Ultrathin poly(vinyl chloride) films with asymmetric surface properties were prepared by incorporating an amphiphilic ruthenium complex at the air-water interface. Stacked assemblies of the films were constructed to examine second-order nonlinear optical effects under specified conditions: (1) number of stacked films, (2) orientation of the asymmetric surface, and (3) presence (or absence) of gaps between the stacked films. The second harmonic light (SHL) intensity quadratically increased with the number of stacked films, when the films with the same surface orientation were separated by gaps. In the absence of gaps, the SHL intensity increased less sharply with the number of films. Appreciable modification of nonlinear optical properties was suggested on each component of the laminated films. The asymmetric property of the surface was further confirmed by the use of stacked films with alternatively-reversed orientation.