Spectroscopic, electrochemical, and photochemical studies of self-assembled via axial coordination zinc porphyrin-fulleropyrrolidine dyads
Spectroscopic, electrochemical, and photochemical studies of self-assembled via axial coordination zinc porphyrin-fulleropyrrolidine dyads
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DOI：
10.1021/jp013165i
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发表时间：
2002-04-04
影响因子：
2.9
通讯作者：
Ito, O
中科院分区：
文献类型：
--
作者：
D'Souza, F;Deviprasad, GR;Ito, O
研究了含吡啶或咪唑配位配体的四苯基卟啉锌、(TPP)锌和富勒吡咯烷轴向配位形成的自组装给体-受体二元组分的光谱、氧化还原和光化学行为。UV-Vis、H-1NMR和ESI-MS研究以及计算研究表明，电子供体[(TPP)锌]和电子受体富勒吡咯烷实体之间形成了1：1的超分子二联体。测得的生成常数K值顺序为o-吡啶比m-吡啶小得多，与对吡啶相似或相等，比富勒吡咯烷的N-苯基咪唑小得多。热力学参数表明络合反应稳定，络合离解热在26~32kJ·mol~(-1)之间。H-1核磁共振研究表明，吡啶或咪唑配体与(TPP)锌的中心锌发生轴向配位，而在CH2Cl2基质中进行的ESI-MS研究表明，自组装的二联体具有预期的分子离子峰。用从头算B3LYP/3-21G(*)方法研究了二联体的几何结构和电子结构。这些研究表明，(TPP)锌与富勒吡咯烷之间存在稳定的络合作用。最高占据前线分子轨道(HOMO)大部分位于(TPP)锌实体上，而最低未占据分子轨道(LUMO)则完全位于富勒烯实体上。在邻二氯苯，0.1(TBA)ClO4溶液中研究了分离的自组装二元组分的氧化还原行为。在该溶剂的可及电势窗口内，观察到了与锌卟啉环的氧化还原和富勒烯实体的还原对应的7个单电子氧化还原过程。这些电化学结果表明基态组分之间的相互作用很弱。用稳态和时间分辨发射以及瞬时吸收技术对激发态电子转移反应进行了监测。在邻二氯苯中，富勒吡咯烷的吡啶基团或咪唑基团与(TPP)锌配位后，主要的猝灭途径是从单重态激发的(TPP)锌到C-60部分的电荷分离。计算的电荷分离速率在10(7)-10(10)S(-1)之间，取决于富勒吡咯烷的轴向配体(吡啶或咪唑)。然而，在苯腈等配位溶剂中，分子间电子转移主要发生在三重态(TPP)锌原子到C-60原子的转移上。目前的研究还表明，单线态激发的富勒吡咯烷对(TPP)锌的配位很少或没有猝灭。
Spectroscopic, redox, and photochemical behavior of self-assembled donor-acceptor dyads formed by axial coordination of zinc tetraphenylporphyrin, (TPP)Zn, and fulleropyrrolidine bearing either pyridine or imidazole coordinating ligands were investigated. The UV-vis, H-1 NMR, and ESI-mass spectral studies, as well as computational studies, revealed supramolecular 1:1 dyad formation between the electron donor [(TPP)Zn] and the electron acceptor, fulleropyrrolidine entities. The determined formation constant K values followed the order o-pyridyl much less than m-pyridyl similar or equal to p-pyridyl much less than N-phenyl imidazole entities of the fulleropyrrolidine. The evaluated thermodynamic parameters revealed stable complexation with complex dissociation enthalpies ranging between 26 and 32 kJ mol(-1). The H-1 NMR studies revealed axial coordination of the pyridine or imidazole ligands to the central zinc of (TPP)Zn, while the ESI-Mass spectral studies performed in CH2Cl2 matrix revealed the expected molecular ion peak of the self-assembled dyads. The geometric and electronic structures of the dyads were probed using ab initio B3LYP/3-21G(*) methods. Such studies revealed stable complexation between (TPP)Zn and fulleropyrrolidine entities. The majority of the highest occupied frontier molecular orbital (HOMO) was found to be located on the (TPP)Zn entity, while the lowest unoccupied molecular orbital (LUMO) was found to be entirely on the fullerene entity. The redox behavior of the isolated self-assembled dyads was investigated in o-dichlorobenzene, 0.1 (TBA)ClO4. A total of seven one-electron redox processes corresponding to the oxidation and reduction of zinc porphyrin ring, and the reduction of fullerene entities were observed within the accessible potential window of the solvent. These electrochemical results suggest weak interactions between the constituents in the ground state. The excited-state electron-transfer reactions were monitored by both steady-state and time-resolved emission as well as transient absorption techniques. In o-dichlorobenzene, upon coordination of either the pyridine or imidazole entities of fulleropyrrolidine to (TPP)Zn, the main quenching pathway involved charge separation from the singlet excited (TPP)Zn to the C-60 moiety. The calculated rate of charge separation was found to range between 10(7) and 10(10) s(-1) depending upon the axial ligand (pyridine or imidazole) of the fulleropyrrolidine. However, in a coordinating solvent like benzonitrile, intermolecular electron transfer predominantly takes place mainly from the triplet excited (TPP)Zn to the C-60 moiety. The present studies also revealed little or no quenching of the singlet excited fulleropyrrolidine upon coordination of (TPP)Zn.