Dynamics of charge pair generation in ladder-type poly(para-phenylene) at different excitation photon energies -: art. no. 035215

Generation of charge pairs in a ladder-type poly(para-phenylene) was investigated by means of electric field modulated femtosecond pump-probe absorption spectroscopy upon excitation at 3.1 and 4.66 eV. Exciting at 3.1 eV in the optical S-0-->S-1 transition, the number of geminately bound electron-hole pairs rises smoothly within the entire exciton life time. Upon excitation at 4.66 eV an instantaneous generation of geminate pairs superimposed on the more gradual increase is observed. Both processes are field-assisted, albeit differently. The former is attributed to ultrafast dissociation of a hot Franck-Condon state, while the latter is assigned to dissociation of vibrationally relaxed singlet excitons.