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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Intramolecular Energy Transfer in a Covalently Linked Copper(II) Porphyrin-Free Base Porphyrin Dimer: Novel Spin Polarization in the Energy Acceptor
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Intramolecular Energy Transfer in a Covalently Linked Copper(II) Porphyrin-Free Base Porphyrin Dimer: Novel Spin Polarization in the Energy Acceptor

机译：共价连接的铜（II）卟啉无基卟啉二聚体中的分子内能量转移：能量受体中的新型自旋极化。

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摘要

The excitation wavelength dependence of time-resolved EPR is used to demonstrate the pathway of intramolecular energy transfer in a covalently liked copper(II)-free base porphyrin dimer. Spin polarized spectra are presented for selective excitation of both the copper(II) porphyrin donor (at 540 nm) and the free base porphyrin acceptor (at 640 nm) at 50 and 80 K. In all cases the observed spectra are assigned to the triplet state of the free base which is coupled weakly to the copper ground state doublet. The polarization pattern generated by selective excitation of the free base half is indicative of intersystem crossing (ISC), whereas excitation of the copper(II) half gives an eaa/eea polarization pattern. The latter is rationalized in terms of energy transfer via the lowest excited trip-quartet state of the copper(II) moiety, followed by selective depopulation from the spin states with doublet character in the weakly coupled free base triplet-copper doublet system. This leads to a spectrum which resembles that of the free base triplet state with overpopulation of the T_(+1) and T_(-1) sublevels. The spin-selective electronic relaxation is supported by the fact that the rise time of the polarization is consistent with the decay rate of the triplet signal generated via ISC following direct excitation of the free base. Superimposed on these triplet spectra is a narrow emissive feature at g = 2.02 and a very broad a/e pattern, both of which decay with the same rate. In addition, a short-lived absorptive feature at g = 2.00 is observed at temperatures below 50 K. From their g-values and temperature dependence these featrues are tentatively assigned to quartet and doublet states in conformations of the complex in which the coupling between the free base triplet and Cu(II) ground state is strong.
机译：时间分辨的EPR的激发波长依赖性用于证明在共价喜欢的无铜（II）的碱性卟啉二聚体中分子内能量转移的途径。呈现了自旋极化光谱，用于在50和80 K下选择性激发铜（II）卟啉供体（540 nm）和游离碱卟啉受体（640 nm）。在所有情况下，观察到的光谱均分配给三重态弱耦合到铜基态双峰的自由基态。由选择性激发游离碱的一半产生的极化图表明了系统间交叉（ISC），而激发铜（II）的一半给出了eaa / eea极化图。后者在能量转移方面是合理的，它通过铜（II）部分的最低激发三重态达到四重态，然后在弱耦合的游离碱三重态-铜二重态系统中，从具有二重态特征的自旋态中有选择地减少。这导致了一个光谱，该光谱类似于游离基三重态的光谱，其中T _（+ 1）和T _（-1）子级人口过多。自旋选择性电子弛豫得到以下事实的支持：极化的上升时间与在直接激发游离碱后通过ISC生成的三重态信号的衰减率一致。叠加在这些三重态光谱上的是g = 2.02时的窄发射特征和非常宽的a / e图案，两者均以相同的速率衰减。此外，在低于50 K的温度下，观察到g = 2.00的短时吸收特征。根据其g值和温度依赖性，这些特征被暂定为四重态和二重态，其形式为：游离碱三重态和Cu（II）基态很强。

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