Effect of Ultraviolet Irradiation on Proton Transfer Facilitated by 5,10,15,20-Tetraphenyl-21H,23H-porphine and Its Metal Complexes at a Water/1,2-Dichloroethane Interface

Abstract

We examined photochemical effects by ultraviolet irradiation on facilitated proton transfer at a water/1,2-dichloroethane (W/DCE) interface by ion-transfer voltammetry using a Xe flash lamp. 5,10,15,20-Tetraphenyl-21H,23H-porphine (HTPP) or its metal complex, such as cobalt (Co(II)TPP), zinc (Zn(II)TPP), and nickel (Ni(II)TPP) complexes, was added into the DCE phase as an ionophore for the facilitated proton transfer. After we irradiated the W/DCE interface through the W phase, the voltammetric waves for proton transfer facilitated by HTPP and Co(II)TPP were remarkably enhanced and shifted to the lower potential region, compared to those before irradiation. We confirmed from the pH and argentometric titrations that such enhancements and shifts of the waves were caused by hydrogen chloride (HCl) produced by photodecomposition of DCE. On the other hand, the waves for proton transfer facilitated by Zn(II)TPP and Ni(II)TPP were very small from the beginning, and showed neither enhancement nor any shift upon irradiation.

Ion-Transfer Voltammetry at a Water/1,2-Dichloroethane Interface Using Photoionization by Ultraviolet Irradiation: Detection of Cation Radicals of p-Phenylenediamine Derivatives

“…In order to solve this problem, we have been attempting to photoionize electrically neutral substances by using ultraviolet irradiation. In a previous paper, 5 we reported that DCE, serving as a solvent of an organic phase consisting of a W/DCE interface, was photochemically decomposed to hydrogen chloride (HCl) by ultraviolet irradiation from a Xe flash lamp (200 -300 nm); we also confirmed that facilitated proton-transfer by 5,10,15,20-tetraphenyl-21H,23Hporphine or its cobalt(II) complex was greatly enhanced. However, an ion transferring across the W/DCE interface in this work is a proton, but not an ion directly photoionized by ultraviolet irradiation.…”

“…This is because pH of the W phase was lowered than the initial pH of an unbuffer W phase with hydrogen chloride generated through photodecomposition of DCE by ultraviolet irradiation. 5 Namely, it can be concluded that the second wave observed after ultraviolet irradiation and the third wave observed before ultraviolet irradiation are both an ion transfer of TMPDH + from the W phase to the DCE phase. The pH dependences of Ipa were almost the same for both before and after irradiation, as can be seen from Fig.…”

“…The other is the photodecomposition of DCE to form hydrogen chloride (HCl). 5 Since HCl formed in the DCE phase readily dissolves into the W phase as hydrochloric acid and lowers pH of the W phase, a wave for the ion transfer of TMPDH + , which has already been distributed into the W phase before the voltammetric measurement, is expected to shift to a more negative potential region compared with that before ultraviolet irradiation. Based on these expectations, the waves observed in the cyclic voltammograms were investigated in more detail.…”

“…the W/DCE interface used in this work is the same as that used in previous work. 5 Ultraviolet light was supplied from a Xe flash lamp (Hamamatsu, SQ type, L 2359) covered with UV glass, which was driven at 400 Hz with an electronic source (Hamamatsu, C3684) and a function synthesizer (NF, 1930A). The Xe flash lamp has a spectral range of from 185 to 2000 nm, and several bright lines below an absorption edge of DCE saturated with water, approximately 300 nm.…”

Prediction of the Standard Gibbs Energy of Ion Transfer across the 1,2-Dichloroethane/Water Interface

“…[13][14][15][16][17] Furthermore, since DCE has no absorption in the visible light region, the DCE/W system is suitable for spectroelectrochemical measurements [18][19][20][21] and also for studies of photo-induced electrochemical reactions. [22][23][24][25] Thus, it would be useful to predict ∆ !" ∘,!→!…”