SURFACE-PLASMON-RESONANCE INVESTIGATIONS OF LANGMUIR-BLODGETT-FILMS OF DONOR-ACCEPTOR SUBSTITUTED POLYENES - LINEAR OPTICAL AND ELECTROOPTIC PROPERTIES

We present surface-plasmon-resonance (SPR) investigations on Langmuir-Blodgett films of two different types of donor-acceptor substituted polyenes. SPR spectroscopy in Kretschmann configuration enables determination of thickness and dielectric constants of films down to the monolayer range. The linear electro-optic susceptibilities chi(2)(-omega;omega,0) of mono- and multi-layer films are determined as dielectric constant changes DELTAepsilon, which are seen as field-induced modulations in the mode-coupling condition in prism-coupled SPR. Knowing the magnitude and sign of chi(2)(-omega;omega,0) and the orientation angle of the molecules in the film, obtained from FT-IR spectroscopy, we were able to determine the second hyperpolarisability beta(-omega;omega,0). In films of 7-N,N-dioctylaminophenyl-7,8'-diapocarotene-8'-al, beta is found to have a very high value of 7.7 x 10(-47) cm3/V2. The dependence of beta on the film deposition type is discussed.