PHOTOEXCITATION SPECTROSCOPY - SOLITONS IN PERNIGRANILINE BASE

Pernigraniline base, the fully oxidized form of polyaniline, is the first known system beyond trans-polyacetylene to exhibit a Peierls band gap with a doubly degenerate ground state. The presence of phenyl rings in this system suggests that solitonic and polaronic defects involving changes in the ring angle as well as in the bond length should be considered as the excited states of pernigraniline are studied. The results of near-steady-state and long-time photoinduced absorption and light-induced electron spin resonance studies of pernigraniline will be reviewed. Excitations observed in these experiments differ in associated infrared activity and spin as well as in decay time. The short-lived photoinduced phenomena have been proposed to result from charged soliton-like defects, while the long-lived absorption at 1.5 eV has been suggested to be due to a polaron defect. A new long-lived photoinduced absorption near 1.8 eV that has no observable associated infrared activity is identified with neutral solitons.