The interplay between multiple chromophores in nucleic acids and photosynthetic proteins gives rise to complex electronic phenomena and largely governs the de-excitation dynamics. Electronic coupling between bases in the excited states of single strands of DNA and RNA may extend over several bases and likely protects nucleic acids from harmful UV damage. Here we report on the coupling between bases in single RNA strands of cytosine and find that the excited state is delocalized over up to five bases at neutral pH, where all bases are non-protonated (i.e. neutral). Delocalization is over four bases at 278 nm excitation, while it involves five bases at shorter wavelengths of 188 nm and 201 nm. This is in contrast to only nearest-neighbour interactions for corresponding DNA strands as previously reported. The current results seemingly corroborate earlier findings of larger spatial communication in RNA than in DNA strands of adenine, but there is no obvious link between the overall structure of strands and delocalization lengths. RNA cytosine strands form a tight helix, while comparatively, adenine strands show less tight packing, also compared to their DNA counterparts, and yet exhibit even higher delocalisation.

中文翻译：

---

关于胞嘧啶RNA单链的离域长度：有多少个碱基可以看见光？

核酸中的多个发色团与光合蛋白之间的相互作用产生了复杂的电子现象，并在很大程度上控制了去激励的动力学。DNA和RNA单链处于激发态的碱基之间的电子偶联可能会延伸到多个碱基上，并可能保护核酸免受有害的紫外线损害。在这里，我们报告了胞嘧啶单RNA链中碱基之间的偶联，发现在中性pH值（所有碱基均为非质子化）（即中性）下，激发态在多达五个碱基上离域化。在278 nm激发下，离域作用超过4个碱基，而离焦在188 nm和201 nm的较短波长处涉及5个碱基。这与先前报道的仅对应DNA链的近邻相互作用相反。目前的结果似乎证实了RNA中比腺嘌呤的DNA链更大的空间通讯的早期发现，但是在链的整体结构与离位长度之间没有明显的联系。RNA胞嘧啶链形成紧密的螺旋，而相比之下，腺嘌呤链也比其DNA对应物显示不那么紧密的堆积，但表现出更高的离域度。