Analytic expressions for the complex long-axis linear optical susceptibility ${\chi }_{\mathrm{xx}}$ of parallel, noninteracting trans-polyacetylene and poly(para-phenylene) chains are obtained in terms of the band gap $E_g$ and the π-band width $E_0.$ The fact that the susceptibility expressions show identical dependence on the parameters $E_g$ and $E_0$ leads the way to a general expression for the long-axis linear optical susceptibility of conjugated polymers valid for photon energies around the band gap. The susceptibility expressions include damping and are obtained in the free-carrier dipole approximation using an analytic tight-binding derivation based on carbon $\pi$ electrons only. In addition to the long-axis susceptibilities, the complex short-axis susceptibility ${\chi }_{\mathrm{yy}}$ and off-diagonal susceptibility ${\chi }_{\mathrm{xy}}$ of trans-polyacetylene and the imaginary part of the short-axis susceptibility of poly(para-phenylene) are also derived.

• Received 1 August 2002

DOI:https://doi.org/10.1103/PhysRevB.67.075206