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A Model Exact Study of Two-Photon Absorption Intensities in Oligomers of Thiophene and Pyrrole
Mousumi Das and S. Ramasesha

The two-photon absorption (TPA) intensities of oligomers of thiophene and pyrrole containing up to three rings are computed exactly within the Pariser-Parr-Pople (PPP) model. Correction Vector (CV) technique employed in these calculations takes into account the full singlet space of the system, which in the case of tri-thiophene spans nearly six million basis states. We find that in both systems the TPA cross section is large to the higher lying mAg state, which is characterized by a large transition dipole to the 1Bu state. The energy of the state lies between 1.4 and 1.8 times the optical gap.

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