Regioselective alkylation of 1-(4-pyridyl)-2-[5-(dicyanomethanide)thien-2-yl]ethylene sodium salt (2 )b y a covalently surface-bound benzyl halide (4) produces a polar-ordered zwitterionic thin film (5). Chemisorption of 2 on the coupling layer 4 was monitored by UV-vis spectroscopy, contact-angle measurements, X-ray photoelectron spectroscopy, and second harmonic generation (SHG). Relative to carbanion 2, the film UV-vis spectrum exhibits a red-shifted (¢I 170 nm) charge-transfer band, consistent with quaternization of the pyridyl group of 2 by 4. The nonlinear optical properties of the blue films of 5 were measured by SHG. The average molecular tilt angle of the chromophore was determined to be 46°, and zzz 5.0 10 -8 esu (20 pm/V) was estimated at a fundamental wavelength of 1064 nm.