Inada Taeko, Funasaka Yoko, Kikuchi Koichi, Takahashi Yasutake, Ikeda Hiroshi
Department of Physics, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara 228-8555, Japan.
J Phys Chem A. 2006 Mar 2;110(8):2595-600. doi: 10.1021/jp054027m.
To make the effects of molecular size on photoinduced electron-transfer (ET) reactions clear, the ET fluorescence quenching of aromatic hydrocarbons by trivalent lanthanide ions M3+ (europium ion Eu3+ and ytterbium ion Yb3+) and the following ET reactions such as the geminate and free radical recombination were studied in acetonitrile. The rate constant k(q) of fluorescence quenching, the yields of free radical (phi(R)) and fluorescer triplet (phi(T)) in fluorescence quenching, and the rate constant k(rec) of free radical recombination were measured. Upon analysis of the free energy dependence of k(q), phi(R), phi(T), and k(rec), it was found that the switchover of the fluorescence quenching mechanism occurs at deltaG(fet) = -1.4 to -1.6 eV: When deltaG(fet) < -1.6 eV, the fluorescence quenching by M3+ is induced by a long-distance ET yielding the geminate radical ion pairs. When deltaG(fet) > -1.4 eV, it is induced by an exciplex formation. The exciplex dissociates rapidly to yield either the fluorescer triplet or the geminate radical ion pairs. The large shift of switchover deltaG(fet) from -0.5 eV for aromatic quenchers to -1.4 to -1.6 eV for lanthanide ions is almost attributed to the difference in the molecular size of the quenchers. Furthermore, it was substantiated that the free energy dependence of ET rates for the geminate and free radical recombination is satisfactorily interpreted within the limits of the Marcus theory.
为了弄清楚分子大小对光致电子转移（ET）反应的影响，在乙腈中研究了三价镧系离子M3 +（铕离子Eu3 +和镱离子Yb3 +）对芳烃的ET荧光猝灭以及随后的ET反应，如双自由基和自由基复合反应。测量了荧光猝灭的速率常数k(q)、荧光猝灭中自由基产率(φ(R))和荧光体三重态产率(φ(T))以及自由基复合的速率常数k(rec)。通过分析k(q)、φ(R)、φ(T)和k(rec)的自由能依赖性，发现荧光猝灭机制转变发生在ΔG(fet) = -1.4至-1.6 eV时：当ΔG(fet) < -1.6 eV时，M3 +引起的荧光猝灭是由长距离ET产生双自由基离子对引起的。当ΔG(fet) > -1.4 eV时，是由激基复合物形成引起的。激基复合物迅速解离，产生荧光体三重态或双自由基离子对。猝灭剂的转变ΔG(fet)从芳烃猝灭剂的-0.5 eV大幅移至镧系离子的-1.4至-1.6 eV，几乎归因于猝灭剂分子大小的差异。此外，还证实了在Marcus理论的范围内，双自由基和自由基复合的ET速率的自由能依赖性得到了令人满意的解释。
