SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION, AND ELECTROOPTICAL PROPERTIES OF NONCENTROSYMMETRIC AZOBENZENE ZIRCONIUM PHOSPHONATE MULTILAYER FILMS/

Ultrathin noncentrosymmetric nonlinear optical films based on zirconiu m phosphonate (ZP) self-assembled multilayers that incorporate the asy mmetric azobenzene chromophore [5-[4-[[4-[(6-hydroxyhexyl)sulfonyl]phe nyl] azo]phenyl]pentoxy]phosphonic acid (HAPA) are synthesized and con structed, The ZP film structure and multilayer deposition chemistry ar e characterized by a combination of polarization/modulation Fourier tr ansform infrared reflection absorption spectroscopy, surface plasmon r esonance (SPR) measurements, and optical second harmonic generation (S HG). SPR measurements on the HAPA multilayer films yield an average mo nolayer thickness of 27 +/- 0.5 Angstrom. The resonant SHG at 365 nm f rom ultrathin HAPA ZP films on silica surfaces increases quadratically with the number of self-assembled HAPA monolayers, and an analysis of the polarization dependence of the surface SHG yields an orientation parameter LI = 0.79 +/- 0.03 corresponding to an average tilt angle of 27 +/- 2 degrees for the azobenzene chromophores with respect to the surface normal. An electro-optic coefficient r(33) for the HAPA monola yers of 11 pm/V at 632.8 nm is obtained from SPR modulation experiment s of ZP films on gold substrates that have been incorporated into air- gap capacitors, SPR modulation experiments are then performed on a HAP A monolayer in an in situ electrochemical environment in order to dete rmine that a modulation of +/- 25 mV corresponds to a change in the el ectric field strength of 1 x 10(-1) V/cm within the ultrathin organic film at the electrode surface.