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)stilb azole nonlinear optical chromophore precursor onto benzyl chloride-pre functionalized surfaces is studied in situ by polarized second harmoni c generation techniques. The measurements reveal that the self-assembl y kinetics are approximately biexponential (I2w1/2 approximately (1-al pha1e(-k1t) -alpha2-k2t)) with a rapid initial phase, followed by a sl ower second phase. The in situ measurements also indicate that the ave rage tilt angle of the chromophore dipole moment direction with respec t to the surface normal increases significantly (approximately 20-degr ees --> 42-degrees) in the initial phases of chromophore adsorption an d then remains nearly constant. These results suggest substantial chro mophore-chromophore electrostatic and steric repulsion as monolayer gr owth proceeds. The maximum chromophore coverage observed corresponds t o approximately 49 angstrom2/molecule and chi(2) = 3 x 10(-7) esu at l ambda = 1064 nm.