Probing of bound electron–hole-pairs by optical re-excitation in a short-chain oligomer

We probe the photoconductive response to optical re-excitation of photoexcitations in a four-member oligophenylenevinylene in a sandwich LED configuration. Re-excitation of the singlet exciton leads to an enhancement of photocurrent (PC). Only excitons in the vicinity of the aluminum electrode give rise to PCs. Also charged photoexcitations can be re-excited to form mobile charge carriers. We show that an increase of PC is only observed during the ultrashort period of geminate recombination, due to optically induced enhancement of the escape probability of the charged pairs.