PICOSECOND PHOTOINDUCED ABSORPTION AND LONG-LIVED EFFECTS IN POLYANILINE

We present results of picosecond photoinduced absorption studies on po ly(pernigraniline base) (PNB), the degenerate-ground-state form of pol yaniline, and poly(emeraldine base), a nondegenerate form. When pumped at, the 2.1 eV absorption edge, both polymers display photoinduced ab sorption in the 1.3-1.6 eV region due to charged polarons. PNB display s additional absorption at >1.5 eV due to neutral solitons. For each o f these polymers, the photogenerated polaron absorption at fixed pump/ probe time delay is found to lose oscillator strength with continued e xposure to the pump beam, decaying in a stretched-exponential manner o ver several minutes and saturating at about 10 percent of its initial value. In PNB, the soliton absorption saturates completely and is repl aced by a slowly-decaying bleaching signal which is comparable in magn itude. We consider a possible origin of these effects to be the buildu p of long-lived electronic states in the polymers.