PHOTOEXCITATION SPECTROSCOPY - SOLITONS IN PERNIGRANILINE BASE

Pernigraniline base, the fully oxidized form of polyaniline, is the fi rst known system beyond trans-polyacetylene to exhibit a Peierls band gap with a doubly degenerate ground state. The presence of phenyl ring s in this system suggests that solitonic and polaronic defects involvi ng changes in the ring angle as well as in the bond length should be c onsidered as the excited states of pernigraniline are studied. The res ults of near-steady-state and long-time photoinduced absorption and li ght-induced electron spin resonance studies of pernigraniline will be reviewed. Excitations observed in these experiments differ in associat ed infrared activity and spin as well as in decay time. The short-live d photoinduced phenomena have been proposed to result from charged sol iton-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 act ivity is identified with neutral solitons.