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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Spectral and density functional studies on the absorbance and fluorescence spectra of 2-R-5-phenyl-1,3,4-oxadiazoles and their conjugate acids
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Spectral and density functional studies on the absorbance and fluorescence spectra of 2-R-5-phenyl-1,3,4-oxadiazoles and their conjugate acids

机译：2-R-5-苯基-1,3,4-恶二唑及其共轭酸的吸光度和荧光光谱的光谱和密度泛函研究

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摘要

Absorption and fluorescence spectra of 2-R-5-phenyl-1,3,4-oxadiazoles (R = H, methyl, tert-butyl, trifluoromethyl, amino, phenyl, benzyl) were studied experimentally and by time dependent density functional theory (TDDFT) methods. In acidic media a substantial red shift is observed due to the presence of conjugate acid forms. Two conjugate acid forms (3H and 4H) are possible for unsymmetrically substituted oxadiazoles. Relative basicities of the two basic centers of oxadiazole ring at the S-0 and S-1 geometries were calculated using the local density descriptors approach. Substituent effects were studied by analyzing the electron density distribution in the ground and excited states. Analyzing the absorption spectra and local descriptors results, we predict 4H forms to be the dominant acid forms. Calculated emission peaks of 4H forms agree well with experimental observations. An abnormal red shift in the case of the 3H forms is attributed to the increased stabilization of the N-H bond in the 3H forms compared to the 4H forms.
机译：实验研究了2-R-5-苯基-1,3,4-恶二唑（R = H，甲基，叔丁基，三氟甲基，氨基，苯基，苄基）的吸收和荧光光谱，并根据时间依赖性密度泛函理论（ TDDFT）方法。在酸性介质中，由于存在共轭酸形式，观察到明显的红移。对于不对称取代的恶二唑，可能有两种共轭酸形式（3H和4H）。使用局部密度描述符方法计算了在S-0和S-1几何结构的恶二唑环的两个基本中心的相对碱性。通过分析基态和激发态下的电子密度分布，研究了取代基效应。分析吸收光谱和局部描述符结果，我们预测4H形式是主要的酸形式。计算出的4H形式的发射峰与实验观察结果非常吻合。 3H形式的异常红移归因于3H形式中的N-H键与4H形式相比增加了稳定性。

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