Understanding the kinetics and energetics of photoinduced electron transfer (PET) reactions is of considerable research interest in photochemical sciences. In this study, interactions between trivalent lanthanide ions (Ln(III)) as electron acceptors and coumarin dyes as electron donors have been investigated in aqueous media using ground state absorption, steady-state (SS) emission, time-resolved (TR) fluorescence and laser flash photolysis (LFP) techniques. Among different Ln(III) ions, only Eu(III), Yb(III) and Sm(III) are found to display substantial interaction with the excited singlet (S₁) state of the coumarin dyes, which correspond well with the favorable free energy changes (negative ΔG⁰) associated with the PET reactions in these coumarin-Ln(III) systems. For other Ln(III) ions, as ΔG⁰ is not favorable, they do not show any interaction with the excited coumarin dyes. Among the interacting coumarin-Ln(III) systems, bimolecular quenching rate constant (k_q) increases consistently with the increasing exergonicity (−ΔG⁰), when each of the Ln(III) ions are considered independently, except for Eu(III), for which the k_q values have already reached the diffusion controlled limit. However, considering all the Ln(III) ions together, the k_q values do not show any common correlation with the changing ΔG⁰ values. The k_q values are in general much lower for Yb(III) quencher as compared to Sm(III), even though the exergonicity values for coumarin-Yb(III) systems are more favorable than the coumarin-Sm(III) systems. Correlating the observed results based on the diffusion mediated bimolecular reaction model, we infer that depending on the ΔG⁰ values, some Ln(III) quenchers possibly also engage their upper electronic energy states as well to assist multichannel ET with the excited coumarin donors, and thereby modulating the k_q values very substantially for different coumarin-Ln(III) systems. Apparently, the involvement of multichannel ET causes the total reorganization energy (λ) for ET reactions to differ largely for different Ln(III) ions, which would otherwise be very similar for all the coumarin-Ln(III) pairs. Observed results suggest that the intramolecular reorganization energy (λ_i) associated with lower electronic states of the hydrated Ln(III) ions is much larger than that associated with higher electronic states of these ions. While the involvement of multichannel ET is itself an intriguing inference, modulation in the ET kinetics and total λ values for different Ln(III) quenchers through the differential participation of the multichannel PET is also expected to find potential uses in the controlled utilization of such PET reactions in many practical areas.

在光化学领域，了解光诱导电子转移（PET）反应的动力学和能量学具有相当大的研究兴趣。在这项研究中，使用基态吸收，稳态（SS）发射，时间分辨（TR）荧光在水性介质中研究了作为电子受体的三价镧系离子（Ln（III））与作为电子供体的香豆素染料之间的相互作用和激光闪光光解（LFP）技术。在不同的Ln（III）离子中，仅发现Eu（III），Yb（III）和Sm（III）与香豆素染料的激发单线态（S ₁）表现出实质性相互作用，这与良好的游离态非常吻合。能量的变化（ΔG负⁰）与这些香豆素-Ln（III）系统中的PET反应有关。对于其他LN（III）离子，如ΔG ⁰是不利的，它们不显示与激发香豆素染料的任何相互作用。间相互作用的香豆素-LN（III）系统，双分子猝灭速率常数（k _q）与增加exergonicity（-ΔG持续增大⁰），当每个LN（III）离子被独立地考虑，除铕（III） ，其k _q值已达到扩散控制极限。然而，考虑到所有的LN（III）离子一起，第k _q值不显示出与变化ΔG任何共同关联⁰值。第k _q尽管香豆素-Yb（III）系统的能动性值比香豆素-Sm（III）系统更有利，但Yb（III）淬灭剂的Sb值通常比Sm（III）低得多。关联基于介导的双分子反应模型中的扩散所观察到的结果，我们推断，这取决于ΔG ⁰值，一些LN（III）的淬灭剂也可能从事其上的电子能量状态，以及协助多信道ET与激发香豆素供体，和从而针对不同的香豆素-Ln（III）系统非常显着地调节k _q值。显然，多通道ET的参与会导致总重组能量（λ），因为不同的Ln（III）离子的ET反应差异很大，否则所有香豆素-Ln（III）对的反应都非常相似。观察到的结果表明，分子内重组能（λ_我与水合LN（III）离子的低电子状态相关联）比与这些离子的更高电子态相关联的大得多。尽管多通道ET的参与本身是一个有趣的推断，但通过多通道PET的不同参与，对不同Ln（III）淬灭剂的ET动力学和总λ值的调节也有望在这种PET的可控利用中找到潜在的用途。在许多实际领域的反应。