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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Spin dynamics of photogenerated triradicals in fixed distance electron donor-chromophore-acceptor-TEMPO molecules
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Spin dynamics of photogenerated triradicals in fixed distance electron donor-chromophore-acceptor-TEMPO molecules

机译：固定距离电子给体-发色团-受体-TEMPO分子中光生三基团的自旋动力学

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摘要

The stable free radical 2,2,6,6-tetramethylpiperidinoxyl (TEMPO, T-center dot) was covalently attached to the electron acceptor in a donor-chromophore-acceptor (D-C-A) system, MeOAn-6ANI-Ph-n-A-T-center dot, having well-defined distances between each component, where MeOAn-p-methoxyaniline, 6ANI = 4-(N-piperidinyl)naphthalene- 1, 8-dicarboximide, Ph = 2,5-dimethylphenyl (n = 0,1), and A = naphthalene-1,8: 4,5-bis(dicarboximide) (NI) or pyromellitimide (PI). Using both time-resolved optical and EPR spectroscopy, we show that T-center dot influences the spin dynamics of the photogenerated triradical states (2,4)(MeOAn(+center dot)-6ANI-Ph-n-A(-center dot)- T-center dot), resulting in modulation of the charge recombination rate within the triradical compared with the corresponding biradical lacking T-center dot. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn(+center dot) and A(-center dot) is not altered by the presence of T-center dot, which interacts most strongly with A(-center dot) and accelerates radical pair intersystem crossing. Charge recombination within the triradicals results in the formation of (2,4)(MeOAn-6ANI-Ph-n-(NI)-N-3*-T-center dot) or (2,4)(MeOAn-(3*)6ANI-Ph-n-PI-T-center dot) in which T-center dot is strongly spin polarized in emission. Normally, the spin dynamics of correlated radical pairs do not produce a net spin polarization; however, the rate at which the net spin polarization appears on T-center dot closely follows the photogenerated radical ion pair decay rate. This effect is attributed to antiferromagnetic coupling between T-center dot and the local triplet state (NI)-N-3*, which is populated following charge recombination. These results are explained using a switch in the spin basis set between the triradical and the three-spin charge recombination product having both T-center dot and (NI)-N-3* or (3*)6ANI present.
机译：稳定的自由基2,2,6,6-四甲基哌啶氧基（TEMPO，T-中心点）在供体-生色团-受体（DCA）系统中共价附于电子受体，MeOAn-6ANI-Ph-nAT-中心点，在各组分之间具有明确定义的距离，其中MeOAn-对甲氧基苯胺，6ANI = 4-（N-哌啶基）萘-1、8-二甲酰亚胺，Ph = 2,5-二甲基苯基（n = 0,1）和A ＝萘1.8：4，5-双（二甲叉酰亚胺）（NI）或均苯四甲酰亚胺（PI）。使用时间分辨光学和EPR光谱，我们表明T中心点影响光生三基态（2,4）（MeOAn（+中心点）-6ANI-Ph-nA（-中心点）- T中心点），与相应的缺少T中心点的双基点相比，导致三基团内电荷复合率的调制。 T中心点的存在不会改变光生自由基MeOAn（+中心点）和A（中心点）之间的自旋-自旋交换相互作用，T中心点与A（中心点）相互作用最强并加速自由基对系统间交叉。三基内的电荷重组导致形成（2,4）（MeOAn-6ANI-Ph-n-（NI）-N-3 * -T-中心点）或（2,4）（MeOAn-（3 * ）6ANI-Ph-n-PI-T-中心点），其中T-中心点在发射中强烈自旋极化。通常，相关基团对的自旋动力学不会产生净自旋极化。但是，净自旋极化出现在T中心点上的速率紧随光生自由基离子对的衰减速率。此效应归因于T中心点与局部三重态（NI）-N-3 *之间的反铁磁耦合，该电荷在电荷重组后产生。使用三自由基和三主轴电荷重组产物之间同时存在T中心点和（NI）-N-3 *或（3 *）6ANI的自旋基组中的开关来解释这些结果。

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