CHROMOPHORIC SELF-ASSEMBLED NLO MULTILAYER MATERIALS - REAL-TIME OBSERVATION OF MONOLAYER GROWTH AND MICROSTRUCTURAL EVOLUTION BY IN-SITU 2ND-HARMONIC GENERATION TECHNIQUES

The self-assembling adsorption/quaternization of a (dialkylamino)stilbazole nonlinear optical chromophore precursor onto benzyl chloride-prefunctionalized surfaces is studied in situ by polarized second harmonic generation techniques. The measurements reveal that the self-assembly kinetics are approximately biexponential (I2w1/2 approximately (1-alpha1e(-k1t) -alpha2-k2t)) with a rapid initial phase, followed by a slower second phase. The in situ measurements also indicate that the average tilt angle of the chromophore dipole moment direction with respect to the surface normal increases significantly (approximately 20-degrees --> 42-degrees) in the initial phases of chromophore adsorption and then remains nearly constant. These results suggest substantial chromophore-chromophore electrostatic and steric repulsion as monolayer growth proceeds. The maximum chromophore coverage observed corresponds to approximately 49 angstrom2/molecule and chi(2) = 3 x 10(-7) esu at lambda = 1064 nm.