Photoinitiated multistep charge separation in ferrocene-zinc porphyrin-diiron hydrogenase model complex triads
Photoinitiated multistep charge separation in ferrocene-zinc porphyrin-diiron hydrogenase model complex triads
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DOI：
10.1039/c1ee01334c
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发表时间：
2011-07-01
影响因子：
32.5
通讯作者：
Wasielewski, Michael R.
中科院分区：
文献类型：
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作者：
Poddutoori, Premaladha;Co, Dick T.;Wasielewski, Michael R.
两个共价连接的线性电子给体-受体三联体Fc-ZnTPP-[NMI-Fe-I-Fe-I-S-2（CO）（6）]（1）和Fc-Ph-ZnTPP-[NMI-Fe-I-Fe-I-S-2（CO）（6）]（2），其由锌内消旋四苯基卟啉（ZnTPP）发色团、萘单酰亚胺二铁氢化酶活性位点模型[NMI-Fe-I-Fe-I-S-2（CO）（6）]组成，和二茂铁（Fc）二次电子给体与它们相应的二联体参考分子ZnTPP-[NMI-Fe-I-Fe-I-S-2（CO）（6）]（3）、Fc-ZnTPP（4）和Fc-Ph-ZnTPP（5）一起被合成沿着。时间分辨瞬态吸收和发射研究表明，ZnTPP在三单元组1和2中的选择性光激发导致（1）*ZnTPP的两种竞争猝灭途径：电子从（1）*ZnTPP转移到[NMI-Fe-I-Fe-I-S-2（CO）（6）]和能量从（1）*ZnTPP转移到低激发态Fc。我们对参考二联体4和5的研究表明，由激光脉冲产生的大部分（1）*ZnTPP通过三联体1中的能量转移到Fc而快速衰减（τ < 10 ps），而电子转移到[NMI-Fe-I-Fe-I-S-2（CO）（6）]在三联体2中占主导地位，允许从Fc到ZnTPP+的第二快速电子转移步骤进行。完全电荷分离态Fe +-ZnTPP-[NMI-Fe-0-Fe-I-S-2（CO）（6）]和Fe +-Ph-ZnTPP-[NMI-Fe-0-Fe-I-S-2（CO）（6）]的量子产率分别为0.13和0.71。Fc+-ZnTPP-[NMI-Fe-0-FeI-S-2（CO）（6）]中的电荷复合发生，对于Fc（+）-Ph-ZnTPP-[ NMI-Fe-0-FeI-S2（CO）6]，tau（CR）= 9 +/-1 ns和tau（CR）= 67 +/-2 ns。通过引入二次电子供体，还原的二铁氢化酶模拟物的寿命延长了>450倍。使用1和2的光化学析氢的研究表明，氢的产生效率取决于最终电荷分离态的寿命。以逐步方式执行多电子质子耦合电子转移机制的能力将使我们能够研究每个步骤的结构和电子要求，以帮助整体系统优化。因此，可以使用已经用于延长光驱动供体-受体系统中的电荷分离态的寿命的相同的多步电子转移策略，以延长在催化质子还原中潜在使用的金属络合物的还原态的寿命。
Two covalently linked linear electron donor-acceptor triads Fc-ZnTPP-[NMI-Fe-I-Fe-I-S-2(CO)(6)] (1) and Fc-Ph-ZnTPP-[NMI-Fe-I-Fe-I-S-2(CO)(6)] (2) consisting of a zinc meso-tetraphenylporphyrin (ZnTPP) chromophore, a naphthalene monoimide diiron hydrogenase active site model [NMI-Fe-I-Fe-I-S-2(CO)(6)], and a ferrocene (Fc) secondary electron donor have been synthesized along with their corresponding dyad reference molecules ZnTPP-[NMI-Fe-I-Fe-I-S-2(CO)(6)] (3), Fc-ZnTPP (4), and Fc-Ph-ZnTPP (5). Time-resolved transient absorption and emission studies in CH2Cl2 show that selective photoexcitation of ZnTPP in triads 1 and 2 results in two competing quenching pathways for (1)*ZnTPP: electron transfer from (1)*ZnTPP to [NMI-Fe-I-Fe-I-S-2(CO)(6)] and energy transfer from (1)*ZnTPP to low-lying Fc excited states. Our studies on reference dyads 4 and 5 show that the majority of (1)*ZnTPP produced by the laser pulse decays rapidly by energy transfer to Fc in triad 1 (tau < 10 ps), while electron transfer to [NMI-Fe-I-Fe-I-S-2(CO)(6)] dominates in triad 2, allowing the second rapid electron transfer step from Fc to ZnTPP+ to proceed. Quantum yields of the fully charge separated states Fc+-ZnTPP-[NMI-Fe-0-Fe-I-S-2(CO)(6)] and Fc+-Ph-ZnTPP-[NMI-Fe-0-Fe-I-S-2(CO)(6)] are 0.13 and 0.71, respectively. Charge recombination in Fc+-ZnTPP-[NMI-Fe-0-Fe-I-S-2(CO)(6)] occurs with tau(CR) = 9 +/- 1 ns and tau(CR) = 67 +/- 2 ns for Fc(+)-Ph-ZnTPP-[ NMI-Fe-0-FeI-S2(CO)6]. By incorporating a secondary electron donor, the lifetime of the reduced diironhydrogenase mimic was extended by a factor of >450. Studies of photochemical hydrogen evolution using 1 and 2 reveal that the hydrogen generation efficiency depends on the lifetime of the final charge separated state. The ability to execute a multi-electron proton-coupled electron transfer mechanism in a stepwise manner will allow us to investigate the structural and electronic requirements for each step aiding in overall system optimization. Thus, it is possible to use the same multi-step electron transfer strategy that has been employed to extend the lifetime of charge-separated states in photodriven donor-acceptor systems to extend the lifetime of the reduced states of metal complexes of potential use in catalytic proton reduction.