Electron-transfer mechanisms with photoactivated quinones. The encounter complex versus the Rehm-Weller paradigm
Electron-transfer mechanisms with photoactivated quinones. The encounter complex versus the Rehm-Weller paradigm
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DOI：
10.1021/ja982710z
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发表时间：
1999-03-03
影响因子：
15
通讯作者：
Kochi, JK
中科院分区：
文献类型：
--
作者：
Hubig, SM;Kochi, JK
光激发的醌（Q*）通过电子转移（ET）被多甲苯（ArH）有效地猝灭。然而，二阶速率常数（k（2））表现出与自由能（Δ G（ET））的λ m-Weller（外球）依赖性。尽管我们的新发现是猝灭通过一系列具有实质性（电荷转移）键合的相当强的遭遇络合物[Q*，ArH]发生。相对较高的形成常数（K-EC）的遭遇复合物表明，任何机制的解释所观察到的速率常数的驱动力依赖性是非常模糊的，因为k（2）必须是一个复合物的K-EC和内在的速率常数（k（ET））的电子转移的中间（内球）复杂。因此，重组能量提取从Alumm-Weller图缺乏热力学意义。另一方面，明确的驱动力依赖性的k（ET）代表了一个独特的例子，为“正常”马库斯行为的吸能电子转移之间的供体/受体对之间的货车德瓦尔斯接触作为现存的遭遇复杂。
Photoexcited quinones (Q*) are efficiently quenched by polymethylbenzenes (ArH) via electron transfer (ET). However, the second-order rate constants (k(2)) exhibit Rehm-Weller (outer-sphere) dependence an the free energy (Delta G(ET)). despite our new findings that the quenching occurs via a series of rather strong encounter complexes [Q*, ArH] with substantial (charge-transfer) bonding. The relatively high formation constants (K-EC) Of the encounter complexes indicate that any mechanistic interpretation of the driving-force dependence of the observed rate constants is highly ambiguous since k(2) must be a composite of K-EC and the intrinsic rate constant (k(ET)) for electron transfer within the intermediate (inner-sphere) complex. As such, the reorganization energies extracted from Rehm-Weller plots lack thermodynamic significance. On the other hand, the unambiguous driving-force dependence of k(ET) represents a unique example For the "normal" Marcus behavior of the endergonic electron transfer between the donor/acceptor pair in van der Waals contact as extant in the encounter complex.