Charge Transfer and Spin Dynamics in a Zinc Porphyrin Donor Covalently Linked to One or Two Naphthalenediimide Acceptors
Charge Transfer and Spin Dynamics in a Zinc Porphyrin Donor Covalently Linked to One or Two Naphthalenediimide Acceptors
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DOI：
10.1021/acs.jpca.0c10471
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发表时间：
2021-01-15
影响因子：
2.9
通讯作者：
Wasielewski, Michael R.
中科院分区：
文献类型：
--
作者：
Bancroft, Laura;Zhang, Jinyuan;Wasielewski, Michael R.
研究了5，10，15-三（正戊基）-20-苯基卟啉锌（ZnP）电子给体与萘-1，8：4，5-二（二甲酰亚胺）（NDI）电子受体之间的量子相干效应.在295 K下，1和2在甲苯中的光激发后，飞秒瞬态吸收光谱表明，2的电子转移（ET）速率常数比1的大约3倍，这可以解释为非相干ET的统计性质以及电荷分离反应的电子耦合。相比之下，1的电荷复合（CR）的速率常数比2的快约25%。利用飞秒瞬态红外光谱和理论分析，我们发现，在NDI 2中心点-在2本地化到两个NDI之一之前，CR，从而排除电子相干CR从NDI 2中心点-。相反，1和2中的CR是自旋相干的，如通过观察到CR之后的（3）*ZnP产率中的共振作为施加磁场的函数所指示的，分别给出2 J = 210和236 mT的自旋-自旋交换相互作用能，其中2的共振的线宽大于1。这些数据表明，虽然CR是一个自旋相干的过程，在2中的两个NDI之间的电子的非相干跳跃，与缺乏上述的离域一致，导致在2中相对于1更大的自旋退相干。
Quantum coherence effects on charge transfer and spin dynamics in a system having two degenerate electron acceptors are studied using a zinc 5,10,15-tri(n-pentyI)-20-phenylporphyrin (ZnP) electron donor covalently linked to either one or two naphthalene-1,8:4,5-bis(dicarboximide) (NDI) electron acceptors using an anthracene (An) spacer, ZnP-An-NDI (1) and ZnP-An-NDI2 (2), respectively. Following photoexcitation of 1 and 2 in toluene at 295 K, femtosecond transient absorption spectroscopy shows that the electron transfer (ET) rate constant for 2 is about three times larger than that of 1, which can be accounted for by the statistical nature of incoherent ET as well as the electron couplings for the charge separation reactions. In contrast, the rate constant for charge recombination (CR) of 1 is about 25% faster than that of 2. Using femtosecond transient infrared spectroscopy and theoretical analysis, we find that the electron on NDI2 center dot- in 2 localizes onto one of the two NDIs prior to CR, thus precluding electronically coherent CR from NDI2 center dot-. Conversely, CR in both 1 and 2 is spin coherent as indicated by the observation of a resonance in the (3)*ZnP yield following CR as a function of applied magnetic field, giving spin-spin exchange interaction energies of 2J = 210 and 236 mT, respectively, where the line width of the resonance for 2 is greater than 1. These data show that while CR is a spin-coherent process, incoherent hopping of the electron between the two NDIs in 2, consistent with the lack of delocalization noted above, results in greater spin decoherence in 2 relative to 1.