Picosecond photoionization and geminate recombination in an organic donor-acceptor complex

The initial steps involved in the charge separation process in thin films of the organic charge-transfer complex formed from poly-N-vinylcarbazole (PVK) and 2,4,7-trinitro-9-fluorenone (TNF) are observed directly using polarization selective pico-second transient grating techniques. When forming a grating with parallel polarized writing beams, a nonexponential decay of the transient grating signal is observed. When forming a grating with perpendicularly polarized writing beams, the decay of the transient grating signal is observed to increase and to be described adequately as a single exponential. These transient grating signals have been investigated as a function both of an applied electric field and as a function of the TNF ratio. All of these results are consistent with a four-level kinetic model that includes charge hopping, geminate recombination, and field-assisted charge separation. © 1992.