We have attempted to control the helical pitch of a chiral nematic liquid crystal by the use of a photoresponsive chiral metal complex. For this purpose, a novel Ru(III) complex [Ru(acac)(2)(L)] was synthesized, where acac and L denote acetylacetonato and 1,3-bis-{4-[6-(4-phenylazo-phenoxy)-hexyloxy]-phenyl}-propane-1,3- dionato, respectively. The complex underwent cis-trans photoisomerization in methanol when under UV (lambda(max) = 360 nm) or visible (lambda(max) = 450 nm) light illumination, respectively. When the complex was doped into a room-temperature nematic liquid crystal (ZLI-1132), it induced a chiral nematic phase. Under illumination with UV or visible light, the helical pitch of the chiral nematic phase could be changed reversibly by up to 50%. Corresponding to this change, the helical twisting power (HTP) of the complex varied between 34.0 and 22.0 mu m(-1), or between -43.9 and -26.6 mu m(-1) at 35.0 degrees C, where the positive and negative signs corresponded to the Lambda- and Delta-enantiomers, respectively. This has been the first attempt at combining the Delta Lambda chirality of an octahedral metal complex with the cis-trans isomerization of an azobenzene group in the development of a photoresponsive dopant.