Quantum-chemical investigation of the electroabsorption spectra of directly meso-meso-linked porphyrin arrays: essential role of charge-transfer excited states accidentally overlapping with soret bands.
Quantum-chemical investigation of the electroabsorption spectra of directly meso-meso-linked porphyrin arrays: essential role of charge-transfer excited states accidentally overlapping with soret bands.
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DOI：
10.1021/jp040570b
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发表时间：
2005-02
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影响因子：
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通讯作者：
Y. Matsuzaki;A. Nogami;Y. Iwaki;N. Ohta;N. Yoshida;N. Aratani;A. Osuka;Kazuyoshi Tanaka
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文献类型：
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作者：
Y. Matsuzaki;A. Nogami;Y. Iwaki;N. Ohta;N. Yoshida;N. Aratani;A. Osuka;Kazuyoshi Tanaka
在INDO/S-SCI水平上，用态求和（SOS）方法研究了meso-meso直接连接的卟啉（Zn，n = 1-3）阵列的电吸收光谱. Zn（n >或= 2）的实验EA谱在激子分裂低能B（x）带处呈现出与Z1的一阶导数谱相反的不寻常的二阶导数线形，这很容易归因于B（Soret）带的二次Stark位移。虽然二阶导数线形通常归因于基态和激发态之间的永久偶极矩（Deltamu）的差异，但由于它们本质上是D（2）（d）或D（2）（h）对称性，因此对于Zn，二阶导数线形应该是零。正如我们以前的研究所指出的，卟啉间的电荷转移（CT）激发态与激子B带偶然地重叠，并且计算表明B（x）态通过跃迁偶极矩与两个CT态强耦合.这些情况引起了二次斯塔克效应的B（x）带之间的斯塔克位移（一阶导数）和斯塔克加宽（二阶导数）的中间，并发挥了核心作用，建立异常的二阶导数性质的EA光谱。此外，基于理论和实验光谱之间的比较，必须有一个额外的因素，进一步增强的二阶导数性质的EA光谱的卟啉阵列。讨论这个问题，包括溶剂（PMMA）引起的不对称性的作用的初步调查也被提出。
The electroabsorption (EA) spectra of directly meso-meso-linked porphyrin arrays (Zn, n = 1-3) have been investigated by means of the sum-over-states (SOS) approach at the INDO/S-SCI level theory. The experimental EA spectra of Zn (n > or = 2) exhibit an unusual second-derivative line shape at the exciton split low-energy B(x) band in contrast to the first-derivative spectrum of Z1, which is readily ascribed to a quadratic Stark shift of the B (Soret) band. Although the second-derivative line shape is usually attributed to a difference in the permanent dipole moment (Deltamu) between the ground and excited states, it should be vanishing for Zn due to their essentially D(2)(d) or D(2)(h) symmetry. As pointed out in our previous studies, the interporphyrinic charge-transfer (CT) excited states are accidentally overlapping with the excitonic B bands and the present calculations reveal that the B(x) state is strongly coupled via a transition dipole moment with two such CT states. These situations give rise to a quadratic Stark effect on the B(x) band that is intermediate between Stark shift (first derivative) and Stark broadening (second derivative), and play a central role in establishing the anomalous second derivative nature of the EA spectrum. Moreover, based on the comparison between the theoretical and experimental spectra, there must be an additional factor that further enhances the second derivative nature of the EA spectrum of porphyrin arrays. Discussions on this issue including the preliminary investigations on the role of solvent (PMMA)-induced asymmetry are also presented.