Аннотация:A weak polarization response of the photoexcited states of a conjugated pi -electron chain is investigated by cw photoinduced polarimetry. The experiments are carried out with films and solutions of isotropic nano-poly(acetylene) at room temperature. It is found that the polarization response is caused by a weak linear dichroism of the long-lived excited state of nano-trans-poly(acetylene) with a ratio of approximately=0.6 between the absorption coefficients of light polarized transverse to and along the polymer chain. It is suggested that the pi electrons in long-lived states of nano-trans-poly(acetylene) are localized at several C-C bond lengths. (15 References).