Photoinduced Electron Transfer of 5,10,15,20-Tetraphenylporphyrinato Zinc(II) at the Polarized Water/1,2-Dichloroethane Interface

Abstract

The photocurrent at the polarized water/1,2-dichloroethane (DCE) interface was successfully observed in the presence of a lipophilic sensitizer, 5,10,15,20-tetraphenylporphyrinato zinc (ZnTPP), in the organic phase. The photocurrent transient responses were apparently affected by the employed organic supporting electrolyte: tetrapenthylammonium tetraphenylborate (TPnATPB) or tris(tetraoctylammonium)tungstophosphate ((TOcA)₃PW₁₂O₄₀). The photocurrent measured in the TPnATPB system exhibited rather slow responses associated with the ion transfer of photoproducts. On the other hand, the photoinduced heterogeneous electron transfer could be observed in the use of (TOcA)₃PW₁₂O₄₀. The photocurrent intensity in the (TOcA)₃PW₁₂O₄₀ system exhibited an apparent pH dependence and the photoreduction of hydrogen ions probably took place at the water/DCE interface. By analyzing the real and imaginary components of the photocurrent depending on the photoexcitation frequency, we roughly estimated the phenomenological rate constants of the product separation (k_ps) and recombination (k_rec) processes as log(k_ps/s^-1) = 1.5 ± 0.2 and log(k_rec/s^-1) = 1.8 ± 0.1, respectively.