Mechanism of transient photoinduced absorption in conjugated polymers

We examine theoretically two possible origins of transient photoinduced abs orption of conjugated polymers absorption from all exciton-polaron with B-u symmetry and front the optically forbidden 2A(g) State. Exact calculations for the Pariser-Parr-Pople (PPP) model demonstrate that absorption spectra from 2A(g) and from IB, are quite similar when their energies are nearly d egenerate. We discuss the effects of lattice relaxation on spectral feature s and the natures of transitions ill absorption from 1B(u) within configura tion-interaction calculations of the PPP model.