Institute of Chemistry, University of Silesia, Katowice, Poland.
J Phys Chem A. 2012 Mar 8;116(9):2117-30. doi: 10.1021/jp210950n. Epub 2012 Feb 27.
Polarized IR spectra of 2-thiopheneacetic acid and of 2-thiopheneacrylic acid crystals were measured at 293 and 77 K in the υ(O-H) and υ(O-D) band frequency ranges. The corresponding spectra of the two individual systems strongly differ, one from the other, by the corresponding band shapes as well as by the temperature effect characterizing the bands. The crystal spectral properties remain in close relation with the electronic structure of the two different molecular systems. We show that a vibronic coupling mechanism involving the hydrogen bond protons and the electrons on the π- electronic systems in the molecules determines the way in which the vibrational exciton coupling between the hydrogen bonds in the carboxylic acid dimers occurs. Strong coupling in 2-thiopheneacrylic acid dimers prefers a "tail-to-head"-type Davydov coupling widespread by the π- electrons. A weak through-space coupling in 2-thiopheneacetic acid dimers, of a van der Waals type, is responsible for a "side-to-side"-type coupling. The relative contribution of each exciton coupling mechanism in the dimer spectra generation is temperature and the molecular electronic structure dependent. This explains the observed difference in the temperature- induced evolution of the compared spectra.
2-噻吩乙酸和 2-噻吩丙烯酸晶体的极化红外光谱分别在 293 和 77 K 下的 υ(O-H)和 υ(O-D)波段频率范围内进行了测量。这两个单独体系的相应光谱彼此强烈不同，不仅表现在相应的谱带形状上，还表现在特征谱带的温度效应上。晶体光谱性质与两个不同分子体系的电子结构密切相关。我们表明，涉及氢键质子和分子中π-电子系统上的电子的振子耦合机制决定了羧酸二聚体之间氢键的振动激子耦合发生的方式。2-噻吩丙烯酸二聚体中的强耦合优先采用由π-电子广泛传播的“尾到头”型 Davydov 耦合。2-噻吩乙酸二聚体中的弱范德华型的通过空间耦合导致“侧到侧”型耦合。每个激子耦合机制在二聚体光谱产生中的相对贡献取决于温度和分子电子结构。这解释了所观察到的比较光谱在温度诱导下的演化差异。
