Ultrafast Spectroscopy of Even Parity States in pi-Conjugated Polymers

Ultrafast relaxation dynamics of even parity (A sub g) states in poly(p-phenylene vinylene) derivatives were studied using multiple pulse transient spectroscopy, where two different fsec excitation pulses successively generate odd parity (1B sub u) excitons and then re-excite them to higher A sub g states. For re-excitation energies bar h omega 1.1 eV (mA sub g band) ultrafast internal conversion back to 1B sub u is observed in accordance with Vivilov-Kasha's rule. However, for bar h omega > 1.1 eV (kA sub g band) the decay occurs into a non-emissive state identified as a polaron pair, which indicates that kA sub 6 is dramatically different from mA sub g and may belong to another excitation manifold.