Langmuir-Blodgett films of indandione-1,3 pyridinium betaine. III: Linear dichroism and non-linear optical properties

Linear dichroism and second-harmonic generation (SHG) have been measured in Langmuir-Blodgett (LB) multilayers of Z-type structure of amphiphilic indandione-1,3 pyridinium betaine (IPB) with an aliphatic tail containing 17 carbon atoms (C17IPB). The dichroic ratio A_s/A_p of electronic absorption of s- and p-polarised light and the SHG intensity show that the 'heads' of C17IPB molecules are predominantly oriented along the deposition direction of monolayers on a quartz substrate. Orientation parameters and mean statistical azimuthal and tilt angles are evaluated as a function of the number of monolayers. The SHG efficiency has been measured in C17IPB monolayers on a water surface as a function of surface pressure. The effective hyperpolarisability β of the IPB molecule has been determined experimentally in a chloroform solution by the hyper-Rayleigh-scattering method. The obtained value of β = (138±16) × 10^-30 esu is in good agreement with theoretical estimates.