Design and studies on supramolecular ferrocene-porphyrin-fullerene constructs for generating long-lived charge separated states
Design and studies on supramolecular ferrocene-porphyrin-fullerene constructs for generating long-lived charge separated states
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DOI：
10.1021/jp064504g
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发表时间：
2006-12-21
影响因子：
3.3
通讯作者：
Ito, Osamu
中科院分区：
文献类型：
--
作者：
D'Souza, Francis;Chitta, Raghu;Ito, Osamu
二茂铁-卟啉-富勒烯超分子结构，其中共价连接的二茂铁-卟啉冠醚化合物与烷基铵阳离子功能化富勒烯自组装，已被设计用于实现逐步电子转移和空穴移位，以产生长寿命的电荷分离态。通过DFT B3LYP/3-21G（*）方法进行的计算研究和荧光猝灭研究得出的结合常数表明，采用冠醚-烷基铵阳离子结合策略得到了稳定的共轭物。卟啉腔中不同金属离子的选择改变了电荷分离和电荷结合的自由能变化。自由能计算表明，光诱导的电子转移过程从单重态激发态到所有被研究的超分子二联体和三联体都是放热的。结合时间分辨荧光和纳秒瞬态吸收光谱测量，证实了光致电荷分离和电荷重组过程。在三元组中，富勒烯部分的自由基阴离子的电荷重组过程分为两个步骤，即卟啉阳离子自由基的直接电荷重组和二茂铁阳离子部分的远距离电荷重组。发现第二种途径的电荷复合速率比前一种途径慢一个数量级，从而满足了在超分子体系中产生长寿命电荷分离态的电荷迁移条件。
Supramolecular ferrocene-porphyrin-fullerene constructs, in which covalently linked ferrocene-porphyrincrown ether compounds were self-assembled with alkylammonium cation functionalized fullerenes, have been designed to achieve stepwise electron transfer and hole shift to generate long-lived charge separated states. The adopted crown ether-alkylammonium cation binding strategy resulted in stable conjugates as revealed by computational studies performed by the DFT B3LYP/3-21G(*) method in addition to the binding constants obtained from fluorescence quenching studies. The free-energy changes for charge-separation and chargerecombination were varied by the choice of different metal ions in the porphyrin cavity. Free-energy calculations suggested that the light-induced electron-transfer processes from the singlet excited state of porphyrins to be exothermic in all of the investigated supramolecular dyads and triads. Photoinduced charge-separation and charge-recombination processes have been confirmed by the combination of the time-resolved fluorescence and nanosecond transient absorption spectral measurements. In case of the triads, the charge-recombination processes of the radical anion of the fullerene moiety take place in two steps, viz., a direct charge recombination from the porphyrin cation radical and a slower step involving distant charge recombination from the ferrocene cation moiety. The rates of charge recombination for the second route were found to be an order of magnitude slower than the former route, thus fulfilling the condition for charge migration to generate long-lived chargeseparated states in supramolecular systems.