Eugster Nicolas, Fermín David J, Girault Hubert H
Laboratoire d'Electrochimie Physique et Analytique, Institut de Chimie Moléculaire et Biologique, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
J Am Chem Soc. 2003 Apr 23;125(16):4862-9. doi: 10.1021/ja029589n.
The initial stages of the heterogeneous photoreduction of quinone species by self-assembled porphyrin ion pairs at the water|1,2-dichloroethane (DCE) interface have been studied by ultrafast time-resolved spectroscopy and dynamic photoelectrochemical measurements. Photoexcitation of the water-soluble ion pair formed by zinc meso-tetrakis(p-sulfonatophenyl)porphyrin (ZnTPPS(4)(-)) and zinc meso-tetrakis(N-methylpyridyl)porphyrin (ZnTMPyP(4+)) leads to a charge-separated state of the form ZnTPPS(3)(-)-ZnTMPyP(3+) within 40 ps. This charge-separated state is involved in the heterogeneous electron injection to acceptors in the organic phase in the microsecond time scale. The heterogeneous electron transfer manifests itself as photocurrent responses under potentiostatic conditions. In the case of electron acceptors such as 1,4-benzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and tetrachloro-1,4-benzoquinone (TCBQ), the photocurrent responses exhibit a strong decay due to back electron transfer to the oxidized porphyrin ion pair. Interfacial protonation of the radical semiquinone also contributes to the photocurrent relaxation in the millisecond time scale. The photocurrent responses are modeled by a series of linear elementary steps, allowing estimations of the flux of heterogeneous electron injection to the acceptor species. The rate of electron transfer was studied as a function of the thermodynamic driving force, confirming that the activation energy is controlled by the solvent reorganization energy. This analysis also suggests that the effective redox potential of BQ at the liquid|liquid boundary is shifted by 0.6 V toward positive potentials with respect to the value in bulk DCE. The change of the redox potential of BQ is associated with the formation of hydrogen bonds at the liquid|liquid boundary. The relevance of this approach toward modeling the initial processes in natural photosynthetic reaction centers is briefly discussed.
通过超快时间分辨光谱和动态光电化学测量，研究了自组装卟啉离子对在水|1,2 - 二氯乙烷（DCE）界面上对醌类物质的多相光还原初始阶段。由锌中 - 四（对 - 磺酸钠苯基）卟啉（ZnTPPS(4)(-)）和锌中 - 四（N - 甲基吡啶基）卟啉（ZnTMPyP(4+)）形成 的水溶性离子对的光激发在40皮秒内导致形成ZnTPPS(3)(-)-ZnTMPyP(3+)形式的电荷分离态。这种电荷分离态在微秒时间尺度上参与向有机相中的受体进行多相电子注入。多相电子转移在恒电位条件下表现为光电流响应。对于诸如1,4 - 苯醌（BQ）、2,6 - 二氯 - 1,4 - 苯醌（DCBQ）和四氯 - 1,4 - 苯醌（TCBQ）等电子受体，由于向氧化卟啉离子对的反向电子转移，光电流响应呈现强烈衰减。自由基半醌的界面质子化也在毫秒时间尺度上对光电流弛豫有贡献。光电流响应由一系列线性基本步骤建模，从而能够估计向受体物种的多相电子注入通量。研究了电子转移速率作为热力学驱动力的函数，证实活化能由溶剂重组能控制。该分析还表明，相对于本体DCE中的值，BQ在液 - 液边界处的有效氧化还原电位向正电位偏移了0.6 V。BQ氧化还原电位的变化与液 - 液边界处氢键的形成有关。简要讨论了这种方法对模拟天然光合反应中心初始过程的相关性。
