ELECTRIC-FIELD MEASUREMENTS INSIDE SELF-ASSEMBLED MULTILAYER FILMS ATELECTRODE SURFACES BY ELECTROCHEMICALLY MODULATED SURFACE-PLASMON RESONANCE EXPERIMENTS

The new in situ optical technique of electrochemically modulated surfa ce plasmon resonance (EM-SPR) is described and applied to the measurem ent of the electrostatic fields inside noncentrosymmetric zirconium ph osphonate (ZP) films formed from the asymmetric nonlinear optical mate rial [1-[4-[4-[(N-(2-hydroxyethyl) -N-methyl)amino]phenyl]azo](5-phosp honopentyl)] pyridinium bromide (PY-AZO). In situ EM-SPR measurements on PY-AZO films yield a value for the change in electric field strengt h (Delta E) of 4 x 10(3) V/cm for a change in electrode potential (Del ta phi(m)) at 0.0 V vs. SCE of +/-25 mV (8 x 10(4) V/cm for Delta phi( m) = 1 V). This electric field strength value indicates that there is substantial ion penetration into the film in the electrochemical envir onment. Both the phase and magnitude of the surface optical response i n the EM-SPR measurements are used to distinguish the molecular and me tal electrode contributions to the overall optical signal. These two E M-SPR contributions are identified and separated in a quantitative fas hion through a series of theoretical Fresnel calculations.