A proper understanding of excited state properties of indole derivatives can lead to rational design of efficient fluorescent probes. The optically active $L_a$ and $L_b$ excited states of a series of substituted indoles, where a substituent was placed on position four, were calculated using equation of motion coupled cluster and time dependent density functional theory. The results indicate that most substituted indoles have a brighter second excited state corresponding to experimental absorption maxima, but a few with electron withdrawing substituents absorb more on the first excited state. Absorption on the first excited state may increase their fluorescence quantum yield, making them better probes. Electronic structure methods were found to predict the energies of the systems with electron withdrawing substituents more accurately than those with electron donating substituents. The excited states of both states correlated well with electrophilicity, similar to the experimental trends for the absorption maxima. Overall, these computational studies indicate that theory can be used to predict excited state properties of substituted indoles, when the substituent is an electron withdrawing group.

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模拟取代基对吲哚衍生物电子激发态的影响


正确理解吲哚衍生物的激发态特性可以导致高效荧光探针的合理设计。使用运动方程耦合簇和时间依赖性密度泛函理论计算一系列取代吲哚的光学活性 $L_a$ 和 $L_b$ 激发态，其中取代基位于位置 4。结果表明，大多数取代的吲哚具有对应于实验吸收最大值的更亮的第二激发态，但少数具有吸电子取代基的吲哚在第一激发态上吸收更多。对第一激发态的吸收可能会增加它们的荧光量子产率，使它们成为更好的探针。发现电子结构方法比具有电子供体取代基的系统更准确地预测了系统能量。两种状态的激发态与亲电性密切相关，类似于吸收最大值的实验趋势。总体而言，这些计算研究表明，当取代基是吸电子基团时，理论可用于预测取代吲哚的激发态性质。