Light-induced electron spin polarization in vanadyl octaethylporphyrin: I. Characterization of the excited quartet state
Light-induced electron spin polarization in vanadyl octaethylporphyrin: I. Characterization of the excited quartet state
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DOI：
10.1021/jp0620365
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发表时间：
2006-08-10
影响因子：
2.9
通讯作者：
van der Est, Art
中科院分区：
文献类型：
--
作者：
Kandrashkin, Yuri E.;Asano, Motoko S.;van der Est, Art
本文报道了八乙基钒卟啉在各向同性和部分有序冷冻溶液中的激光诱导自旋极化瞬态电子顺磁共振（TREPR）谱，并与相应的发光数据进行了比较。的TREPR光谱显示出良好的解决超精细耦合钒核和多重极化模式与零场分裂（ESTA）的典型功能。由谱估计的钒超精细耦合张量的主值是从基态的稳态EPR谱发现的相应值的1/3。基于这些特性和数值模拟，我们将偏振模式归属于激发四重态。从模拟的光谱（D = 17.5 mT和E = 1.5 mT）的三重态的三重参数的值是可比的锌和游离碱八乙基卟啉的三重态。自旋极化的寿命被发现是温度依赖性的，基本上是相同的光发射。的温度依赖性是合理的，使用一个模型，其中的衰变到基态发生从trip-quartet和trip-doublet，这是在热平衡，即使在15 K。模型与观测到的自旋极化寿命的拟合产生了三重四重态和三重二重态之间47 cm（-1）的能隙。结果表明，自旋极化演化从一个多重态图案在早期的时间，在后期的净吸收模式以下的激光闪光。我们认为热平衡的建立导致自旋从多重态向净极化的演化。
Laser flash induced spin-polarized transient electron paramagnetic resonance ( TREPR) spectra for vanadyl octaethylporphyrin in isotropic and partially ordered frozen solutions are presented and compared with corresponding luminescence data. The TREPR spectra show well-resolved hyperfine couplings to the vanadium nucleus and a multiplet polarization pattern with features typical of zero-field splitting ( ZFS). The principal values of the vanadium hyperfine coupling tensor evaluated from the spectra are 1/3 of the corresponding values found from steady-state EPR spectra of the ground state. On the basis of these characteristics and numerical simulations, the polarization patterns are assigned to the excited quartet state. The values of the ZFS parameters of the trip-quartet obtained from simulation of the spectra ( D = 17.5 mT and E = 1.5 mT) are comparable to those of the triplet state of the zinc and free base octaethyl porphyrin. The lifetime of the spin polarization is found to be temperature dependent and is essentially the same as that of the optical emission. The temperature dependence is rationalized using a model in which the decay to the ground state occurs from both the trip-quartet and trip-doublet, which are in thermal equilibrium even at 15 K. A fit of the model to the observed spin polarization lifetimes yields an energy gap of 47 cm(-1) between the trip-quartet and trip-doublet. It is shown that the spin polarization evolves from a multiplet pattern at early times to a net absorptive pattern at late times following the laser flash. It is proposed that the establishment of thermal equilibrium leads to the evolution of the spin from multiplet to net polarization.