Cis-transoidal poly[(4-carboxyphenyl)acetyleneI (poly-1) complexed. with optically active amines and amino alcohols showed an induced circular dichroism (ICD) in the ultraviolet-visible region because of a predominantly one-handed helix formation in water and in dimethyl sulfoxide (DMSO). The Cotton effect signs of the poly-1/chiral amino alcohol complexes were inverted in the presence of water, whereas the ICD pattern of the poly-1/chiral amine complexes showed no change, regardless of the water content. These results demonstrated that the helix sense of poly-1 induced by optically active amino alcohols through noncovalent acid-base interactions could be switched by changes in the solvent ratio in the DMSO-water mixtures. (C) 2003 Wiley Periodicals, Inc.