Femtosecond linear dichroism of DNA-intercalating chromophores:: Solvation and charge separation dynamics of [Ru(phen)2dppz]2+ systems
Femtosecond linear dichroism of DNA-intercalating chromophores:: Solvation and charge separation dynamics of [Ru(phen)2dppz]2+ systems
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DOI：
10.1073/pnas.100127397
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发表时间：
2000-05-23
影响因子：
11.1
通讯作者：
Zewail, AH
中科院分区：
文献类型：
--
作者：
Önfelt, B;Lincoln, P;Zewail, AH
DNA嵌入发色团[Ru(phen)(2)dppz](2+)具有独特的光物理性质，其中最引人注目的是与DNA结合时的“光开关”特性。作为二聚体，它充当 DNA 的分子主食，表现出显着的双嵌入拓扑结构。在此，我们报告了单体和共价连接的二聚体发色团的飞秒动力学，它们均游离于水溶液中并与 DNA 复合，瞬时吸收和线性二向色性显示电子弛豫至最低的金属到配体电荷转移 (CT) 状态，据我们所知，首次观察到该发色团的亚皮秒动力学。我们在水溶液中观察到两个不同的弛豫过程，时间常数分别为 700 fs 和 4 ps。有趣的是，这两个时间常数与散装水的重定向模式观察到的时间常数非常相似。 700-fs 工艺涉及重大的二色性变化。我们将这些观察结果与电荷分布的变化以及 CT 状态溶剂化所涉及的时间尺度联系起来。当追逐 DNA 时，单体和二聚体都观察到较慢的过程，寿命约为 7 和 37 ps。这种差异可归因于 DNA 嵌入口袋中经历的结构和电子弛豫的变化。最后，最终金属与配体 CT 态到基态的重组寿命（这是光开关过程的关键）在水溶液中被发现对结构修饰敏感，范围从 [Ru(phen)(2)dppz](2+) 的 260 ps 和单体发色团衍生物的 360 ps 到二聚体的 2.0 ns。这种巨大的变化反映了溶剂化在光开关过程中的直接作用。
The DNA-intercalating chromophore [Ru(phen)(2)dppz](2+) has unique photophysical properties, the most striking of which is the "light-switch" characteristic when binding to DNA. As a dimer, it acts as a molecular staple for DNA, exhibiting a remarkable double-intercalating topology. Herein, we report femtosecond dynamics of the monomeric and the covalently linked dimeric chromophores, both free in aqueous solution and complexed with DNA, Transient absorption and linear dichroism show the electronic relaxation to the lowest metal-to-ligand charge-transfer (CT) state, and subpicosecond kinetics have been observed for this chromophore for what is, to our knowledge, the first time. We observe two distinct relaxation processes in aqueous solution with time constants of 700 fs and 4 ps. Interestingly, these two time constants are very similar to those observed for the reorientational modes of bulk water. The 700-fs process involves a major dichroism change. We relate these observations to the change in charge distribution and to the time scales involved in solvation of the CT state. Slower processes, with lifetimes of approximate to 7 and 37 ps, were observed for both monomer and dimer when hound to DNA, Such a difference can be ascribed to the change of the structural and electronic relaxation experienced in the DNA intercalation pocket. Finally, the recombination lifetime of the final metal-to-ligand CT state to the ground state, which is a key in the light-switch process, is found in aqueous solution to be sensitive to structural modification, ranging from 260 ps for [Ru(phen)(2)dppz](2+) and 360 ps for the monomer chromophore derivative to 2.0 ns for the dimer. This large change reflects the direct role of solvation in the light-switch process.