Hazra Montu K, Chakraborty Tapas
Department of Chemistry, Indian Institute of Technology, Kanpur UP 208016, India.
J Phys Chem A. 2008 Feb 14;112(6):1100-4. doi: 10.1021/jp077584c. Epub 2008 Jan 19.
We have presented in this paper the laser-induced fluorescence excitation and resolved fluorescence spectra of five 1:1 hydrogen-bonded complexes of 2-pyridone (2PY) with formic acid (FA), acetic acid (AA), propanoic acid (PA), formamide (FM), and acetamide (AM). The resolved fluorescence spectra, measured following excitation to different single vibronic levels of the dimers indicate that the intermolecular hydrogen bond vibrations undergo mixing with a number of intramolecular modes of the 2PY moiety in the excited state. A comparison of the emission spectral features of these dimers clearly indicates that the methyl groups belonging to the AA and AM moieties spectacularly accelerate the vibrational energy redistribution (IVR) in the 2PY moiety. On the other hand, although the molecular size of PA is bigger than AA, the spectral features of the 2PY-PA dimer bear signatures of a slower IVR rate compared to those of 2PY-AA. We propose that hyperconjugation of the methyl group with the cyclic hydrogen-bonded network involving AA and AM is responsible for the observed phenomenon.
我们在本文中展示了2-吡啶酮（2PY）与甲酸（FA）、乙酸（AA）、丙酸（PA）、甲酰胺（FM）和乙酰胺（AM）形成的五种1:1氢键复合物的激光诱导荧光激发光谱和分辨荧光光谱。在激发到二聚体的不同单振动能级后测量的分辨荧光光谱表明，分子间氢键振动在激发态下与2PY部分的一些分子内模式发生混合。对这些二聚体发射光谱特征的比较清楚地表明，属于AA和AM部分的甲基显著加速了2PY部分的振动能量重新分布（IVR）。另一方面，尽管PA的分子尺寸大于AA，但与2PY-AA相比，2PY-PA二聚体的光谱特征显示出IVR速率较慢的特征。我们认为，甲基与涉及AA和AM的环状氢键网络的超共轭作用是导致观察到的现象的原因。
