We have prepared the organosulfur self-assembled monolayer (SAM) containing hemicyanine on gold. It shows a large second-order nonlinear optical susceptibility chi(zzz) = 58 pm/V. The adsorption kinetics of the SAM on gold was also probed by the in situ real time measurements of second-harmonic generation (SHG) and surface plasmon resonance (SPR) spectroscopy. While the SHG kinetics was saturated immediately after the immersion of the gold substrate in the solution, the SPR kinetics showed additional slow adsorption for more than 20 000 s. This means that rapid formation of the well-ordered hemicyanine SAM is followed by gradual physisorption where the molecules are disordered. (C) 2002 Elsevier Science B.V. All rights reserved.