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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Cytosine in Context: A Theoretical Study of Substituent Effects on the Excitation Energies of 2-Pyrimidinone Derivatives
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Cytosine in Context: A Theoretical Study of Substituent Effects on the Excitation Energies of 2-Pyrimidinone Derivatives

机译：上下文中的胞嘧啶：取代基对2-嘧啶酮衍生物激发能的影响的理论研究

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摘要

The ultrafast radiationless decay mechanism for cytosine has been shown to be in part dependent upon high vertical excitation, while slower fluorescence displayed in some cytosine analogs is generally linked to lower vertical excitation energies. To probe how excitation energies relate to pyrimidine structure, substituent effects on the vertical excitation energies for a number of derivatives of 2-pyrimidin-(1H)-one (2P) have been calculated using multireference configuration-interaction ab initio methods. Substitutions using groups with pi electron donating, withdrawing and conjugation-extending properties at the C~4 and C~5 positions on the 2P system give predictive trends for the first three singlet excited-state energies. The S_1 pi pi* energies of 2P derivatives involving C~4 substitution vary linearly with the Hammett substituent parameter sigma_P~+. Cytosine is shown to have the highest bright pi pi* energy of the 2P derivatives presented, with that energy being strongly dependent on the position, orientation, and geometry of the C~4-amino. A simple description of the predictive energetic trends for the bright pi pi* energies using frontier molecular orbital theory is presented, based on the character of the HOMO and LUMO orbitals for each derivative. The results of this study expand the current understanding of the photophysical behavior of the DNA pyrimidine bases and could be useful in the design of analogs where particular spectral properties are desired.
机译：业已证明，胞嘧啶的超快无辐射衰变机理部分取决于高垂直激发，而在某些胞嘧啶类似物中显示的荧光较慢通常与较低的垂直激发能有关。为了探究激发能如何与嘧啶结构相关，已使用多参考构型-相互作用从头算方法计算了2-嘧啶-（1H）-一（2P）衍生物对垂直激发能的取代基效应。使用在2P系统的C〜4和C〜5位置具有pi电子供体，吸出和共轭扩展性质的基团进行的取代，给出了前三个单重态激发态能量的预测趋势。涉及C〜4取代的2P衍生物的S_1 pi pi *能随Hammett取代基参数sigma_P〜+线性变化。胞嘧啶显示出所呈现的2P衍生物具有最高的亮pi pi *能量，该能量强烈依赖于C〜4-氨基的位置，方向和几何形状。基于每种衍生物的HOMO和LUMO轨道的特征，利用前沿分子轨道理论对明亮pi pi *能量的预测性能量趋势进行了简单描述。这项研究的结果扩大了目前对DNA嘧啶碱基的光物理行为的了解，并且在需要特殊光谱特性的类似物设计中可能有用。

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