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首页> 外文期刊>Chemistry: A European journal >Comparative Electrochemical and Photophysical Studies of Tetrathiafulvalene-Annulated Porphyrins and Their Zn~(II) Complexes: The Effect of Metalation and Structural Variation
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Comparative Electrochemical and Photophysical Studies of Tetrathiafulvalene-Annulated Porphyrins and Their Zn~(II) Complexes: The Effect of Metalation and Structural Variation

机译：四硫富富瓦烯环化的卟啉及其锌〜（II）配合物的电化学和光物理比较研究：金属化和结构变化的影响

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摘要

A series of tetrathiafulvalene (TTF)-annulated porphyrins, and their corresponding Zn~(II) complexes, have been synthesized. Detailed electrochemical, photophysical, and theoretical studies reveal the effects of intramolecular charge-transfer transitions that originate from the TTF fragments to the macrocyclic core. The incremental synthetic addition of TTF moieties to the porphyrin core makes the species more susceptible to these chargetransfer (CT) effects as evidenced by spectroscopic studies. On the other hand, regular positive shifts in the reduction signals are seen in the squarewave voltammograms as the number of TTF subunits increases. Structural studies that involve the tetrakis-substituted TTF-porphyrin (both free-base and Zn~(II) complex) reveal only modest deviations from planarity. The effect of TTF substitution is thus ascribed to electronic overlap between annulated TTF subunits rather than steric effects. The directly linked thiafulvalene subunits function as both p acceptors as well as s donors. Whereas s donation accounts for the substituent-dependent charge-transfer transitions, it is the pacceptor nature of the appended tetrathiafulvalene groups that dominates the redox chemistry. Interactions between the subunits are also reflected in the square-wave voltammograms. In the case of the free-base derivatives that bear multiple TTF subunits, the neighboring TTF units, as well as the TTF~(·+) generated through one-electron oxidation, can interact with each other; this gives rise to multiple signals in the square-wave voltammograms. On the other hand, after metalation, the electronic communication between the separate TTF moieties becomes restricted and they act as separate redox centers under conditions of oxidation. Thus only two signals, which correspond to TTF~(·+) and TTF~(2+), are observed. The reduction potentials are also seen to shift towards more negative values after metalation, a finding that is considered to reflect an increased HOMO-LUMO gap. To probe the excited-state dynamics and internal CT character, transient absorption spectral studies were performed. These analyses revealed that all the TTF-porphyrins of this study display relatively short excited-state lifetimes, which range from 1 to 20 ps. This reflects a very fast decay to the ground state and is consistent with the proposed intramolecular charge-transfer effects inferred from the ground-state studies. Complementary DFT calculations provide a mechanistic rationale for the electron flow within the TTF-porphyrins and support the proposed intramolecular chargetransfer interactions and p-acceptor effects.
机译：合成了一系列四硫富瓦烯（TTF）环化的卟啉及其相应的Zn〜（II）配合物。详细的电化学，光物理和理论研究揭示了从TTF片段到大环核的分子内电荷转移跃迁的影响。光谱研究表明，在卟啉核心中向TTF部分增加的合成添加使该物种更容易受到这些电荷转移（CT）的影响。另一方面，随着TTF亚基数目的增加，在方波伏安图中可以看到还原信号的正向正位移。涉及四取代的TTF-卟啉（游离碱和Zn〜（II）配合物）的结构研究表明，与平面度的偏差很小。因此，将TTF取代的作用归因于环状TTF亚基之间的电子重叠，而不是空间效应。直接连接的硫富瓦烯亚基既充当p受体又充当s供体。尽管供体解释了取代基依赖性的电荷转移跃迁，但连接的四硫富富瓦烯基团的受体性质决定了氧化还原化学。亚基之间的相互作用也反映在方波伏安图中。在带有多个TTF亚基的游离碱衍生物的情况下，相邻的TTF单元以及通过单电子氧化生成的TTF〜（·+）可以彼此相互作用。这会在方波伏安图中产生多个信号。另一方面，在金属化之后，单独的TTF部分之间的电子通信受到限制，并且它们在氧化条件下充当单独的氧化还原中心。因此，仅观察到对应于TTF_（·+）和TTF_（2+）的两个信号。在金属化之后，还可以看到还原电位向更多的负值移动，这一发现被认为反映了增加的HOMO-LUMO间隙。为了探测激发态动力学和内部CT特性，进行了瞬态吸收光谱研究。这些分析表明，本研究的所有TTF-卟啉均显示出相对较短的激发态寿命，范围为1至20 ps。这反映出到基态的快速衰减，并且与从基态研究推断出的拟议的分子内电荷转移效应相一致。补充的DFT计算为TTF-卟啉中的电子流动提供了机械原理，并支持提出的分子内电荷转移相互作用和p受体效应。

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