ULTRAFAST FIELD-INDUCED DISSOCIATION OF EXCITONS IN A CONJUGATED PORPHYRIN POLYMER

We present a study of field-induced modulation of the ultrafast transi ent photo-induced response in a conjugated zinc porphyrin polymer. Thi s was in the form of aggregated strands in a host polymer matrix. The photobleaching of the polymer Q-band is significantly reduced by the a pplication of an electric field. This field modulation occurs at very short times (< 0.4 ps). We attribute this to field-assisted dissociati on of excitons to give charge separation, as supported by the measured photovoltaic response. By the measurement of the field-dependent phot o-induced Q-band bleaching, we are able to extend the study of the pho togeneration of charge in conjugated polymers to very much shorter tim es than hitherto. Our results indicate that charge generation is close ly coupled with exciton formation. (C) 1997 Published by Elsevier Scie nce B.V.