INTRAMOLECULAR PHOTOINDUCED CHARGE SEPARATION AND CHARGE RECOMBINATION OF THE PRODUCT ION-PAIR STATES OF A SERIES OF FIXED-DISTANCE DYADS OF PORPHYRINS AND QUINONES - ENERGY-GAP AND TEMPERATURE DEPENDENCES OF THE RATE CONSTANTS
INTRAMOLECULAR PHOTOINDUCED CHARGE SEPARATION AND CHARGE RECOMBINATION OF THE PRODUCT ION-PAIR STATES OF A SERIES OF FIXED-DISTANCE DYADS OF PORPHYRINS AND QUINONES - ENERGY-GAP AND TEMPERATURE DEPENDENCES OF THE RATE CONSTANTS
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DOI：
10.1021/ja00066a036
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发表时间：
1993-06-30
影响因子：
15
通讯作者：
MARUYAMA, K
中科院分区：
文献类型：
--
作者：
ASAHI, T;OHKOHCHI, M;MARUYAMA, K
利用皮秒-飞秒激光光谱研究了自由基卟啉或锌卟啉与醌类化合物的分子内光诱导电荷分离（CS）和产物离子对（IP）态的电荷复合（CR），以考察非极性介质中CS和CR反应的能隙和温度依赖性.得到的CS率在正常区域，到附近的顶部区域，和CR率在倒置区域;它们的能隙依赖性在室温下近似再现的半经典公式考虑到高频量子模式的核振动，虽然CS率附近的顶部区域没有显示出的迹象，相反的计算。我们已经证实，CS反应的激活势垒的增加与减少的能隙，而CR过程是activationless，表明在倒置区域的高频量子模式的主导作用。然而，我们很难找到重组能量等的最佳参数值，该理论方程能同时定量地再现CS和CR速率的能隙依赖性和温度依赖性。我们还研究了溶剂极性对能隙的影响（-DELTAG（CS））的CS速率常数（k（CS））的依赖性，其显示了相当大的系统变化，对应于溶剂重组能随溶剂极性的增加而增加，而能隙随溶剂极性的增加而增加。CR速率常数（k（CR））的（-DELTAG（CR））依赖性显示出很小的溶剂极性依赖性，导致在接近顶部区域的法线中的k（CS）对-DELTAG（CS）曲线与在接近顶部区域的反转中的k（CR）对-DELTAG（CR）曲线之间的交叉。这些结果的影响，这似乎很难解释的基础上，传统的电子转移理论，讨论的基础上的量子力学隧道在倒置区域和/或IP状态和周围的极性溶剂之间的非线性或一些特定的相互作用的存在的主导作用。
Intramolecular photoinduced charge separation (CS) and charge recombination (CR) of the product ion pair (IP) state of a series of fixed-distance dyads consisting of free-base porphyrin or zinc porphyrin and quinones have been investigated by means of picosecond-femtosecond laser spectroscopies in order to examine the energy gap and temperature dependences of CS and CR reactions in nonpolar media. Obtained CS rates were in the normal region, up to the neighborhood of the top region, and CR rates were in the inverted region; their energy gap dependences at room temperature were approximately reproduced by a semiclassical formula taking into consideration the high-frequency quantum mode of nuclear vibrations, although the CS rates near the top region did not show indication of the shift to the inverted region, contrary to the calculation. We have confirmed that the activation barrier for the CS reaction increases with a decrease of the energy gap, while the CR process is activationless, indicating the dominant effect of the high-frequency quantum mode in the inverted region. However, we could hardly find optimum parameter values for reorganization energies, etc., in the theoretical equation which could reproduce quantitatively both the energy gap dependence and the temperature dependence of the CS and CR rates at the same time. We have examined also the solvent polarity effect upon the energy gap (-DELTAG(CS)) dependence of the CS rate constant (k(CS)) which showed a rather large systematic change corresponding to the increase of the solvent reorganization energy with the increase of the solvent polarity, while the energy gap (-DELTAG(CR)) dependence of the CR rate constant (k(CR)) showed little solvent polarity dependence, leading to the crossing between the k(CS) vs -DELTAG(CS) curve in the normal to near the top region and the k(CR) vs -DELTAG(CR) in the inverted to near the top region. Implications of these results, which seem difficult to interpret on the basis of the conventional electron-transfer theories, are discussed on the basis of the dominant effect of the quantum mechanical tunneling in the inverted region and/or the existence of nonlinear or some specific interactions between the IP state and the surrounding polar solvent.