Nonlinear optical interactions in Langmuir-Blodgett organic semiconductor heterostructures

Monolayer and multilayer Langmuir-Blodgett films of two systems: (i) polyalkylthiophene and (ii) tetrakis cumylphenoxy phthalocyanines in pure form and mixed phase with octadecanol were prepared. We report here the first observation of a degenerate four wave mixing signal from a monolayer Langmuir-Blodgett film that of phthalocyanine, due to a large resonant third order optical nonlinearity, x⁽³⁾. The effective x⁽³⁾ behaviors of both phthalocyanine and polythiophene Langmuir-Blodgett films were investigated by time-resolved femtosecond degenerate four wave mixing. The polythiophene Langmuir-Blodgett film when doped with iodine was found to be highly conductive. We have also observed a dramatic reduction of the nonlinear reflectivity as a consequence of iodine doping of polythiophene Langmuir-Blodgett films.