Unipolar charge injection from an electrode/fluid interface into a medium of nearly the same dielectric constant as the electrode is studied. For both photohyphen; and dark injection, electrical image forces no longer serve as an impediment to charge detachment. The system investigated is mesotetraphenylporphin (excited in the vishyphen;near UV) in fluorobenzene solution against tin oxide electrodes. Despite polarity of the medium, photocurrent is extrinsic, with both dark and photocurrent injection occurring at the positive electrode. Both show saturation with applied field in accordance with a model based on forced diffusion theory. In addition, interfacial charge generation and recombination rates are extractable from the data. This method shows promise as a way to study these as a function of excited state and dielectric properties of the system.
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