Within a rigid-band correlated electron model for oligomers of poly-(paraphenylene) (PPP) and poly-(paraphenylenevinylene) (PPV), we show that there exist two fundamentally different classes of two-photon Ag states in these systems to which photoinduced absorption (PA) can occur. At relatively lower energies there occur Ag states which are superpositions of one electron–one hole (1e–1h) and two electron–two hole (2e–2h) excitations, that are both comprised of the highest delocalized valence-band and the lowest delocalized conduction-band states only. The dominant PA is to one specific member of this class of states (the mAg). In addition to the above class of Ag states, PA can also occur to a higher energy kAg state whose 2e–2h component is different and has significant contributions from excitations involving both delocalized and localized bands. Our calculated scaled energies of the mAg and the kAg agree reasonably well to the experimentally observed low- and high-energy PA’s in PPV. The calculated relative intensities of the two PA’s are also in qualitative agreement with experiment. In the case of ladder-type PPP and its oligomers, we predict from our theoretical work an intense PA at an energy considerably lower than the region where PA’s have been observed currently. Based on earlier work that showed that efficient charge-carrier generation occurs upon excitation to odd-parity states that involve both delocalized and localized bands, we speculate that it is the characteristic electronic nature of the kAg that leads to charge generation subsequent to excitation to this state, as found experimentally.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Jun 27 2003|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics