Nonlinear excitations in polyacene

The polyacene chain is viewed as two interacting chains of trans-polyacetylene. the two polyacetylene chains are marked by 1 and 2. The extended SU-Schrieffer-Hedger model of the effects of the inter chain coupling has been used to study the polaronic excitations. We found that the polaron and bipolaron are not stable on chain 1 and spread over chain 2. The linear optical absorption spectrums and the third harmonic generation susceptibilities are found for pristine polyacene chain 1 having polaron or bipolaron. The band edge absorption is found to occur at energy much higher than the band gap energy of the system. This is refereed to the fact that the matrix elements of the oscillator strength of the transition between levels near fermi level is zero. (author). 7 Refs