Provided is a novel ion-pair charge-transfer complex polymer suitable for use as a photo-functional material which shows extremely fast photoresponses in the wide wavelength range from visible to near infrared regions, and thermally stable, wherein the acceptor is a substituted bipyridinium cation expressed by the formula (I) below. In the formula, X represents a group bonded at the 4- or 2-position relative to the nitrogen atoms of the bipyridinium group and selected from the group consisting of phenyl, biphenyl, thienyl, bithienyl, terthienyl, furyl, fluorenyl, pyrenyl, perylenyl, and vinyl groups, or X may not be present so that the pyridinium groups are directly connected; and Z represents a polymer preferably from the ring-opening polymerization of an oxazoline derivative (e.g. one substituted with phenyl group). The anion as the donor is selected, for example, from chloride, bromide, iodide, tetraphenylborate or derivatives thereof.