The relationship between the structures and photoelectrochemical properties of two dyes, cis-dithiocyanato-N,N'-bis(4,4'-dicarboxyl-2,2'-bipyridyl) Ru(II) and cis-dithiocyanato(4,4'-dicarboxyl-2,2'-bipyridyl)-(4,4'-di((N,N-methylphenylamino)methylene)-2,2'-bipyridyl) Ru(II), was examined and compared under the same conditions. Data show that the photophysical properties (including molar extinction coefficients - and excited-state lifetimes) and photoelectrochemical properties (including short-circuit photocurrent, open-circuit photovoltage, incident monochromatic photon to current conversion efficiency, overall energy conversion yield (eta) and transient photocurrent) were changed greatly only due to an acceptor replaced by a donor in one of polypyridyl of the Ru(II) complex, suggesting that the molecular design in energy conversion is very sensitive. (C) 2003 Elsevier Science B.V. All rights reserved.