Abstract. The paper treats the excitonic model of channelrhodopsin (ChR) which consists of dimers, each one connected with two-fold symmetry axis. By using the general theory of molecular excitons and the studies of bacteriorhodpsin (BR), the tensors of dielectric permeability and the gyration tensor are calculated including the contributions of the molecular gyrotropy and of the excitonic coupling. Two cases of refraction in the membrane of ChR are studied: a) normal incidence; b) oblique incidence. The components of refracted waves and the shape of the signal of circular dichroism (CD) are analyzed. The CD spectrum of ChR exhibits a negative couplet in those two cases unlike the case of BR in which couplet disappears at normal incidence.

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