Ultrafast spectroscopy of even-parity states in ∏-conjugated polymers

Relaxation dynamics of even parity (Ag) states in poly(p-phenylene vinylene) derivatives are studied using a novel fsec transient spectroscopy, in which two different excitation pulses successively generate odd parity (1 1Bµ) excitons at 2.2 eV and then reexcite them to higher Ag states. For reexcitation energies hω, <1.1 eV ultrafast internal conversion back to 1 1Bµ takes place in accordance with Vavilov-Kasha's rule. However, for hω >1.1 eV the decay occurs in a nonemissive state identified as a polaron pair, showing that the Ag states above 3.3 eV mediate charge transfer.