Fluorescence of Scopoletin Including its Photoacidity and Large Stokes Shift
Fluorescence of Scopoletin Including its Photoacidity and Large Stokes Shift
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DOI：
10.1007/s10895-019-02471-4
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发表时间：
2019-12-24
影响因子：
2.7
通讯作者：
Muyskens, Mark A.
中科院分区：
文献类型：
--
作者：
Pham, Hunter T.;Yoo, Joy;Muyskens, Mark A.
东莨菪碱在水中具有高荧光性，并作为光酸表现出激发态质子转移（ESPT），与荧光竞争。其吸光度和发射光谱特性使基态和激发态pK(a)值分别为7.4 +/- 0.1和1.4 +/- 0.1。pK(a)*表示ESPT速率常数比伞形虫的速率常数小一个数量级。本报告提供了与硫酸奎宁相当的水中量子产率测量，以及与其他类似香豆素相当的荧光寿命值，但提供了对ESPT过程的深入了解。在四氢呋喃中与强碱反应，观察到东莨菪碱阴离子。在pH值为3 ~ 7的范围内，东莨菪碱的Stokes位移为100 ~ 100 nm，部分原因是其作为光酸的作用。采用密度泛函理论方法进行建模，为实验结果提供了合理的支持。
Scopoletin is highly fluorescent in water and acts as a photoacid exhibiting excited-state proton transfer, ESPT, competitive with fluorescence. Its absorbance and emission spectral characteristics yield ground-state and excited-state pK(a) values of 7.4 +/- 0.1 and 1.4 +/- 0.1, respectively. The pK(a)* implies an ESPT rate constant an order of magnitude smaller than that for umbelliferone. This report provides quantum yield measurements in water that are comparable to quinine sulfate, and fluorescence lifetime values that are on a par with other similar coumarins yet provide insight into the ESPT process. The scopoletin anion is observed in tetrahydrofuran by reaction with a strong base. The Stokes shift of aqueous scopoletin is >100 nm in the pH range 3 to 7 due in part to its action as a photoacid. Modeling by density functional theory methods provides reasonable support for the experimental results.