Optical properties of one-dimensional semiconductors and conjugated polymers

We present a description of the optical properties of one-dimensional semiconductors within the one-electron tight-binding approximation. The case of conjugated carbon chains is explicity considered; the influence of the bond alternation, superalternation, effective heteroatomicity and chain coupling on the optical properties of these systems is evaluated in terms of a simplified but exactly soluble model. It is found that the linear susceptibility in the transparency region of the semiconductor shows a square dependence on a parameter Nd which represents the extent of the electron delocalization. Further the peculiar structure observed in the low-temperature absorption spectrum of the polydiacetylenes is explained in terms of a short-range coupling between chains.