Balan Bijitha, Gopidas Karical R
Photosciences and Photonics Section, Chemical Sciences and Technology Division, Regional Research Laboratory (CSIR), Trivandrum 695019, India.
Chemistry. 2007;13(18):5173-85. doi: 10.1002/chem.200601756.
The self-assembly of a beta-cyclodextrin (beta-CD)-based supramolecular dyad is reported, in which the donor anthracene moiety is covalently linked to the smaller rim of the beta-CD and the acceptor pyromellitic diimide (PMDI) is encapsulated within the beta-CD cavity. Encapsulation of the PMDI into the beta-CD cavity was studied by a variety of techniques, which suggested that PMDI is encapsulated so as to position the aromatic part at the centre of the cavity with the 2-propyl end at the narrower rim among the overhanging primary OH groups and the N-ethylpyridinium end situated at the wider rim exposed to water. Photoinduced electron transfer (PET) in the system was studied by fluorescence quenching and laser flash photolysis techniques. At [PMDI]<10(-4) M, the equilibrium is in favour of the free molecules, and under these conditions fluorescence quenching is negligible and diffusion-mediated electron transfer involving the triplet excited state of anthracene predominates. At higher concentrations of PMDI, the equilibrium is largely in favour of the supramolecular dyad and intra-ensemble PET processes predominate. The experimentally determined electron-transfer rate constant agrees very well with that calculated by using the Marcus equation. It was observed that a fraction of the ion pairs survived for more than 200 micros.
报道了一种基于β-环糊精（β-CD）的超分子二元体系的自组装，其中供体蒽部分共价连接到β-CD的较小边缘，受体均苯四甲酸二酰亚胺（PMDI）被包封在β-CD腔内。通过多种技术研究了PMDI在β-CD腔内的包封情况，结果表明PMDI被包封后，其芳香部分位于腔中心，2-丙基端位于伸出的伯羟基中较窄边缘处，N-乙基吡啶鎓端位于暴露于水的较宽边缘处。通过荧光猝灭和激光闪光光解技术研究了该体系中的光诱导电子转移（PET）。当[PMDI]<10^(-4) M时，平衡有利于游离分子，在此条件下荧光猝灭可忽略不计，涉及蒽三重激发态的扩散介导电子转移占主导。在较高浓度的PMDI下，平衡主要有利于超分子二元体系，体系内PET过程占主导。实验测定的电子转移速率常数与使用Marcus方程计算得到的值非常吻合。观察到一部分离子对存活时间超过200微秒。
