Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States.
J Am Chem Soc. 2015 Mar 25;137(11):3981-90. doi: 10.1021/jacs.5b00977. Epub 2015 Mar 13.
We have prepared a G-quadruplex (GQ-1) that incorporates an 8-(4'-aminophenylethynyl)guanine (GEAn) electron donor covalently attached to a 4-aminonaphthalene-1,8-imide (ANI) chromophore and a naphthalene-1,8:4,5-bis(dicarboximide) (NDI) electron acceptor (GEAn-ANI-NDI, 1). In the presence of KPF6 in tetrahydrofuran (THF), 1 self-assembles into a monodisperse, C4-symmetric GQ-1 with small spatial intraquadruplex overlap between the ANI-NDI units. Photoexcitation of monomeric 1 induces the two-step charge transfer GEAn-(1)*ANI-NDI → GEAn(+•)-ANI(-•)-NDI → GEAn(+•)-ANI-NDI(-•) that occurs in τ(CS1) = 5 ps and τ(CS2) = 330 ps, respectively, while charge recombination in ca. 300 ns. Sharpening of the GEAn(+•) transient absorption and a shift of the ethynyl vibrational frequency in 1 were observed, concomitant with the stepwise electron transfer from ANI(-•) to NDI. Formation of GQ-1 from 1 in THF increases the secondary charge-shifting rate (τ(CS2) = 110 ps) and results in no change in ethynyl vibrational frequency. Charge recombination in GQ-1 is slowed by enhanced radical-pair intersystem crossing driven by the greater number of hyperfine couplings in the assembly. Moreover, time-resolved EPR spectroscopy shows that the spin-spin-exchange interaction (J) between the radicals of GEAn(+•)-ANI-NDI(-•) within GQ-1 is smaller than that of 1, suggesting that the spin (charge) density in GEAn(+•) is more dispersed in GQ-1. The spectroscopic results are consistent with hole sharing among the guanines within the G-quadruplex that is kinetically competitive with the formation of GEAn(+•). This suggests that G-quadruplexes can serve as effective hole conduits in ordered donor-acceptor assemblies.
我们制备了一种 G-四链体 (GQ-1)，其中包含一个共价连接到 4-氨基萘-1,8-亚胺 (ANI) 发色团和萘-1,8:4,5-双(二羧酸二酰亚胺) (NDI) 电子受体的 8-(4'-氨基苯乙炔基)鸟嘌呤 (GEAn) 电子供体 (GEAn-ANI-NDI, 1)。在四氢呋喃 (THF) 中存在 KPF6 的情况下，1 自组装成单分散的、C4 对称的 GQ-1，ANI-NDI 单元之间的空间内四链体重叠较小。单体 1 的光激发诱导两步电荷转移 GEAn-(1)*ANI-NDI → GEAn(+•)-ANI(-•)-NDI → GEAn(+•)-ANI-NDI(-•)，分别发生在 τ(CS1)=5 ps 和 τ(CS2)=330 ps，而在 ca.300 ns 时发生电荷复合。观察到 GEAn(+•)瞬态吸收的锐化和 1 中乙炔振动频率的移动，同时伴随着 ANI(-•)向 NDI 的逐步电子转移。在 THF 中，1 形成 GQ-1 会增加二级电荷转移速率 (τ(CS2)=110 ps)，并且乙炔振动频率没有变化。在组装体中更多的超精细耦合驱动下，自由基对的系间窜越增强，导致 GQ-1 中的电荷复合速度减慢。此外，时间分辨 EPR 光谱表明，GQ-1 中 GEAn(+•)-ANI-NDI(-•)自由基之间的自旋-自旋交换相互作用 (J) 小于 1，表明 GQ-1 中 GEAn(+•)的自旋 (电荷)密度分布更广。光谱结果与 G-四链体内鸟嘌呤之间的空穴共享一致，这与 GEAn(+•)的形成具有动力学竞争。这表明 G-四链体可以作为有序供体-受体组装体中的有效空穴导体。
