Dw. Cheong et al., ORIENTED Z-TYPE LANGMUIR-BLODGETT-FILMS FROM A SOLUBLE ASYMMETRICALLYSUBSTITUTED POLYDIACETYLENE, Macromolecules, 29(5), 1996, pp. 1416-1421
A soluble, asymmetric polydiacetylene has been shown to form stable mo
nolayers at the air-water interface of a Langmuir trough. The monolaye
rs of this unconventional amphiphilic polymer could be repeatedly depo
sited onto hydrophobic substrates during every upstroke cycle of the v
ertical dipping method to form uniform Z-type multilayers. Characteriz
ation of the precise orientation of the polymer main chain has been ca
rried out to determine the spatial correlation between the nonlinear o
ptical chromophore responsible for second-order nonlinear optical prop
erties and the backbone. Polarized UV/vis and IR spectroscopic studies
indicate a preferential orientation of the main chain along the dippi
ng direction with a mean fluctuation of +/-30 degrees between director
axis and chain trajectories. Polarization-dependent second-harmonic g
eneration (SHG) in multilayers indicates a high degree of orientationa
l anisotropy of the backbone. As expected, SHG intensities increase wi
th the number of layers due to the noncentrosymmetric Z-type structure
. The second-order nonlinear coefficient (d(33)) was estimated to be 1
.52 pm/V at 1064 nm of Nd:YAG laser after correcting for absorption. S
urface characterization and alignment of the extended chain backbones
is further established using atomic force microscopy (AFM).