p-Aminothiophenol-capped CdS nanoparticles (8.5 +/- 0.3 nm) were assembled as a monolayer by their electropolymerization into a p-aminothiophenol-monolayer-functionalized Au electrode. The resulting CdS nanoparticle monolayer, 9.0 x 10(11) particles/cm(2), was characterized by AFM, XPS, and microgravimetric quartz crystal microbalance measurements. The dianiline-bridged US nanoparticles assembled on the Au electrode revealed highly efficient photoelectrochemical properties in the presence of triethanolamine as sacrificial electron donor. The dianiline bridging unit was found to have an important function in the photocurrent generation. At an applied potential that is more positive than -0.1 V, the dianiline exists in its oxidized state, and it acts as an electron relay that mediates electron transfer from the semiconductor to the bulk electrode. The quantum yield at an applied potential of 0.4 V corresponds to phi = 5.7%. At an applied potential of less than -0.1 V the polymer exists in its reduced state, and under these conditions the dianiline units act as a tunneling medium for transporting the electrons from the semiconductor nanoparticles to the electrode.