Ultrafast Excited-State Dynamics of Cytosine Aza-Derivative and Analogues
Ultrafast Excited-State Dynamics of Cytosine Aza-Derivative and Analogues
复制标题
胞嘧啶氮杂衍生物和类似物的超快激发态动力学
DOI：
10.1021/acs.jpca.6b12290
复制
发表时间：
2017
影响因子：
2.9
通讯作者：
Li Yongle
中科院分区：
文献类型：
--
作者：
Zhou Zhongneng;Wang Xueli;Chen Jinquan;Xu Jianhua;Zhou Xueyao;Jiang Bin;Li Yongle
通过稳态吸收、荧光和飞秒瞬态吸收测量全面研究了 5-氮杂胞嘧啶 (5-AC)、2,4-二氨基-1,3,5-三嗪 (2,4-DT) 和 2-氨基-1,3,5-三嗪 (2-AT) 的激发态动力学。进行瞬态密度泛函理论 (TDDFT) 计算以帮助分配吸收带并了解激发态衰减机制。首次报道了飞秒时间分辨率的5-AC、2,4-DT和2-AT激发单线态动力学实验结果。在 5-AC 中观察到两种不同的衰变路径，寿命为 ∼1 ps 和数十皮秒。在 2,4-DT 中仅观察到一种寿命为 17 ps 的衰变路径，而在 2-AT 中发现了发射态。 TDDFT 计算表明，5-AC 在第一个允许的 ππ* (S2) 态以下具有暗 nπ*(S1) 态，这导致 ππ* 态的超快衰减。在 2,4-DT 中，亮ππ* (S1) 态以下不存在暗nπ* 态，并且17 ps 寿命被指定为从ππ* (S1) 态到基态的弛豫。在 2-AT 中发现了两个暗 nπ* 态（S1 和 S2），与其他两个相比，它表现出更复杂的激发态动力学。 2-AT 中的光致发光已被证实是来自其明亮ππ* (S3) 态的荧光发射。我们的结果强烈表明电子结构对三嗪环上的取代非常敏感，并且核酸类似物的光物理性质高度依赖于它们的分子结构。
Excited state dynamics of 5-azacytosine (5-AC), 2,4-diamino-1,3,5-triazine (2,4-DT), and 2-amino-1,3,5-triazine (2-AT) were comprehensively investigated by steady state absorption, fluorescence, and femtosecond transient absorption measurements. Time-dependent density functional theory (TDDFT) calculations were performed to help assign the absorption bands and understand the excited state decay mechanisms. The experimental results of excited singlet state dynamics for 5-AC, 2,4-DT, and 2-AT with femtosecond time resolution were reported for the first time. Two distinct decay pathways, with ∼1 ps and tens of picosecond lifetimes, were observed in 5-AC. Only one decay pathway with 17 ps lifetime was observed in 2,4-DT while an emissive state was found in 2-AT. TDDFT calculations suggest that 5-AC has a darknπ*(S1) state below the first allowedππ* (S2) state, which leads to the ultrafast decay of theππ* state. In 2,4-DT, there is no darknπ*state below the brightππ* (S1) state and the 17 ps lifetime is assigned to the relaxation from theππ* (S1) state to ground state. Two darknπ*states (S1and S2) were found in 2-AT, which exhibits much more complex excited state dynamics compared with the other two. Photoluminescence in 2-AT has been confirmed to be fluorescence emission from its brightππ* (S3) state. Our results strongly suggest that electronic structures are very sensitive to the substitution on the triazine ring and that the photophysical properties of nucleic acid analogues depend highly on their molecular structures.