Directly meso-meso linked porphyrin rings:: Synthesis, characterization, and efficient excitation energy hopping
Directly meso-meso linked porphyrin rings:: Synthesis, characterization, and efficient excitation energy hopping
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DOI：
10.1021/ja045254p
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发表时间：
2005-01-12
影响因子：
15
通讯作者：
Osuka, A
中科院分区：
文献类型：
--
作者：
Nakamura, Y;Hwang, IW;Osuka, A
本文以5,10-二芳基锌（II）卟啉为原料，用分步法合成了由4个、6个和8个卟啉组成的直接介中-介中连接的卟啉环CZ4、CZ6和CZ8。通过简单的H-1核磁共振光谱和460 nm左右的非分裂索雷特谱带，表明了对称的环状结构，只有一组卟啉。在B3LYP/6-31G*能级计算的能量最小化结构表明，相邻卟啉之间的二面角按CZ6 > CZ8 > CZ4的顺序减小，这与1H NMR数据一致。通过稳态吸收、荧光、荧光寿命、荧光各向异性衰减和瞬态吸收测量，研究了这些分子的光物理性质。泵浦功率对飞秒瞬态吸收的依赖性和瞬态吸收各向异性衰减曲线都与卟啉环内激发能迁移过程直接相关，其中激子-激子湮灭时间和极化各向异性上升时间用福斯特型非相干能量跳变模型描述得很好。因此，估计了CZ4 (119 +/- 2 fs)（-1）、CZ6 (342 +/- 59 fs)（-1）和CZ8 (236 +/- 31 fs)（-1）的激发能跳变率，反映了相邻卟啉之间电子耦合的大小。总的来说，这些卟啉环作为一个明确的轮状光收集天线模型，在沿环非常有效的激发能量跳跃的光收集天线模型。
Directly meso-meso linked porphyrin rings CZ4, CZ6, and CZ8 that respectively comprise four, six, and eight porphyrins have been synthesized in a stepwise manner from a 5,10-diaryl zinc(II) porphyrin building block. Symmetric cyclic structures have been indicated by their very simple H-1 NMR spectra that exhibit only a single set of porphyrin and their absorption spectra that display a characteristic broad nonsplit Soret band around 460 nm. Energy minimized structures calculated at the B3LYP/6-31G* level indicate that a dihedral angle between neighboring porphyrins decreases in order of CZ6 > CZ8 > CZ4, which is consistent with the 1H NMR data. Photophysical properties of these molecules have been examined by the steady-state absorption, fluorescence, fluorescence lifetime, fluorescence anisotropy decay, and transient absorption measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly related with the excitation energy migration processes within the porphyrin rings, where the exciton-exciton annihilation time and the polarization anisotropy rise time are well described in terms of the Forster-type incoherent energy hopping model. Consequently, the excitation energy hopping rates have been estimated for CZ4 (119 +/- 2 fs)(-1), CZ6 (342 +/- 59 fs)(-1), and CZ8 (236 +/- 31 fs)(-1), which reflect the magnitude of the electronic coupling between the neighboring porphyrins. Overall, these porphyrin rings serve as a well-defined wheel-shaped light harvesting antenna model in light of very efficient excitation energy hopping along the ring.