Spin-multiplicity of a moderately coupled triplet-doublet spin pair in a biphenylene-linked porphyrin dimer
Spin-multiplicity of a moderately coupled triplet-doublet spin pair in a biphenylene-linked porphyrin dimer
复制标题
DOI：
10.1080/00268970600647789
复制
发表时间：
2006-05-20
影响因子：
1.7
通讯作者：
Kaizu, Youkoh
中科院分区：
文献类型：
--
作者：
Asano, Motoko S.;Ishizuka, Kazuhiko;Kaizu, Youkoh
电子自旋瞬变章动谱已应用于中等耦合激发三重态和二重态自旋对。在联亚苯基连接的铜（II）-游离碱卟啉二聚体中，游离碱半或铜半的激光照射导致激发到（pi，pi*）激发态和弛豫到二聚体的最低激发态。在该最低激发态中，最低（pi，pi*）三重态中的游离碱部分与铜卟啉基态二重态偶联，从而形成三重态-二重态自旋对。时间分辨电子顺磁共振（TREPR）光谱的二聚体在冷冻溶液中，在40 K显示更宽的光谱宽度和一个突出的带在光谱的中心比那些为游离碱单体三重态或铜（II）单体卟啉。这些特征与强耦合和弱耦合的三重态二重态自旋对截然不同。用脉冲EPR瞬态章动方法研究了二聚体在三个磁场位置上激发态的自旋多重性。结果表明，自旋多重性在很大程度上取决于磁场。这是合理的，在一个中等大小的耦合。在这种中间耦合的情况下，三重态和二重态基波函数的混合程度很大程度上取决于磁场和分子轴之间的相对取向，因为耦合大小与未扰动物质（三重态和二重态）之间的能量差的比率随磁场方向而变化。部分取向样品的TREPR谱的分裂表明，交换耦合垂直杆J垂直杆约为10 mT，这合理地匹配脉冲实验的结果。
Electron spin transient nutation spectroscopy has been applied to a moderately coupled excited triplet and doublet spin-pair. In a biphenylene-linked copper(II)-free base porphyrin dimer, laser irradiation of either the free base half or the copper half, leads to excitation to the (pi, pi*) excited states and relaxation to the lowest excited state of the dimer. In this lowest excited state, the free base moiety in the lowest (pi,pi*) triplet state is coupled to the copper porphyrin ground doublet state, and thus forming a triplet-doublet spin pair. Time-resolved electron paramagnetic resonance (TREPR) spectra of the dimer in frozen solution at 40K show much wider spectral width and a prominent band in the centre of the spectra than either of those for the free base monomer triplet or that of the copper( II) monomer porphyrin. These features are quite different from the strongly-coupled and weakly-coupled triplet doublet spin pairs. Transient nutation method by pulsed EPR is used to examine the spin-multiplicity of the excited state in the dimer at three magnetic field positions. It was found that spin-multiplicity depends largely on the magnetic field. This is rationalized in terms of an intermediate size of coupling. In such intermediate coupling cases, the degree of mixing of the triplet and doublet basis wavefunctions depends greatly on the relative orientation between magnetic field and molecular axis because the ratio of the coupling size to an energy difference between the unperturbed species, triplet and doublet, varies with magnetic field direction. A splitting of TREPR spectra in partially oriented samples suggests that exchange coupling vertical bar J vertical bar is around 10 mT, which reasonably matches the results of the pulsed experiments.