ORIENTED Z-TYPE LANGMUIR-BLODGETT-FILMS FROM A SOLUBLE ASYMMETRICALLYSUBSTITUTED POLYDIACETYLENE

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).