Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany.
Phys Chem Chem Phys. 2011 Mar 14;13(10):4686-92. doi: 10.1039/c0cp02142c. Epub 2011 Jan 31.
Tautomeric effects in the UV-absorption of trans-urocanic acid in the gas phase are investigated by means of quantum chemical calculations of sixteen tautomers at different levels, followed by absorption cross section simulations. It is shown that several trans tautomers give significant contributions to the total spectrum and that cis tautomers should not contribute to the spectrum at room temperature. The spectra of tautomers protonated at the N1 site of the imidazole ring are strongly red shifted in comparison to the spectra of tautomers protonated at the N3 site. As a consequence, excitation of the first absorption band at different wavelengths produces very different tautomeric populations. This effect helps to explain specific features observed in dispersion emission spectroscopy as well as the anomalous photophysics of urocanic acid.
通过对 16 种互变异构体在不同水平上的量子化学计算，以及随后的吸收截面模拟，研究了气相中天冬氨酸酸反式异构体在紫外吸收中的互变异构效应。结果表明，几种反式互变异构体对总光谱有显著贡献，而顺式互变异构体在室温下不应对光谱有贡献。与 N3 位质子化的互变异构体相比，咪唑环 N1 位质子化的互变异构体的光谱有明显的红移。因此，在不同波长下激发第一吸收带会产生非常不同的互变异构体分布。这种效应有助于解释在色散发射光谱中观察到的特定特征以及尿刊酸异常的光物理性质。
