Intensity-dependent excitonic dephasing in polyaniline

The first observation of light intensity-dependent dephasing time, τ2, of molecular excitons in polyaniline is reported. Using time-resolved four-wave mixing we observed an increase of τ2 when the pump intensity is increased. This unusual behavior is attributed to the excitation of torsional Raman modes associated to the phenyl rings, which contribute to strong confinement of the molecular excitons, as well as to blue shift the polyaniline energy gap and intragap energy levels.