Ultrafast field-induced dissociation of excitons in a conjugated porphyrin polymer

We present a study of field-induced modulation of the ultrafast transient photo-induced response in a conjugated zinc porphyrin polymer. This was in the form of aggregated strands in a host polymer matrix. The photobleaching of the polymer Q-band is significantly reduced by the application of an electric field. This field modulation occurs at very short times (< 0.4 ps). We attribute this to field-assisted dissociation of excitons to give charge separation, as supported by the measured photovoltaic response. By the measurement of the field-dependent photo-induced Q-band bleaching, we are able to extend the study of the photogeneration of charge in conjugated polymers to very much shorter times than hitherto. Our results indicate that charge generation is closely coupled with exciton formation.