The ground- and excited-state electronic interactions between the nucleobase analog 8-(4′-phenylethynyl)deoxyguanosine, EG, with natural nucleobases and 7-deazaguanine, as well as between adjacent EG base analogs, have been characterized using a combination of steady-state spectroscopy and time-resolved fluorescence, absorption, and stimulated Raman spectroscopies. The properties of the nucleoside EG-H₂ are only weakly perturbed upon incorporation into synthetic DNA hairpins in which thymine, cytosine or adenine are the bases flanking EG. Incorporation of the nucleoside to be adjacent to guanine or deazaguanine results in the formation of short-lived (40–80 ps) exciplexes, the charge transfer character of which increases as the oxidation potential of the donor decreases. Hairpins possessing two or three adjacent EG base analogs display exciton-coupled circular dichroism in the ground state and form long-lived fluorescent excited states upon electronic excitation. Incorporation of EG into the helical scaffold of the DNA hairpins places it adjacent to its neighboring nucleobases or a second EG, thus providing the close proximity required for the formation of exciplex or excimer intermediates upon geometric relaxation of the short-lived EG excited state. The three time-resolved spectroscopic methods employed permit both the characterization of the several intermediates and the kinetics of their formation and decay.

中文翻译：

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嘌呤碱基衍生物8-苯基乙炔基鸟嘌呤在DNA发夹中的荧光准分子和激基复合物

核碱基类似物8​​-（4'-苯基乙炔基）脱氧鸟苷EG与天然核碱基和7-脱氮鸟嘌呤之间以及相邻的EG碱基类似物之间的基态和激发态电子相互作用已经通过稳定的组合进行了表征态光谱和时间分辨的荧光，吸收和受激拉曼光谱。仅当掺入以胸腺嘧啶，胞嘧啶或腺嘌呤为EG侧基的合成DNA发夹中时，核苷EG-H ₂的特性才会受到微弱的干扰。。与鸟嘌呤或脱氮鸟嘌呤相邻的核苷掺入会导致形成短寿命的（40–80 ps）激基复合物，其电荷转移特性随供体氧化电位的降低而增加。具有两个或三个相邻EG碱基类似物的发夹在基态下显示激子耦合的圆二色性，并在电子激发时形成长寿命的荧光激发态。将EG掺入DNA发夹的螺旋支架中使其与邻近的核碱基或第二个EG相邻，从而在短暂EG的几何弛豫后提供形成激基复合物或受激准分子中间体所需的紧密邻近性兴奋的状态。所采用的三种时间分辨光谱方法既可以表征几种中间体，也可以分析其形成和衰变的动力学。