Abstract

Terahertz spectroscopic studies of 4-octyloxybenzoic acid, 4-decyloxybenzoic acid and 4-hexylbenzoic acid liquid crystals were performed using the Fourier Transform Infrared method. The materials are characterized by distinct absorption bands in the 6–18 terahertz frequency range. A good correspondence was observed between the experimental frequencies and theoretical frequencies of the single molecule obtained by Density Functional Theory calculations for all the three compounds. The spectra of the studied compounds had three bands, which appeared at similar frequencies and with the same vibration modes. 4-Octyloxybenzoic acid, 4-decyloxybenzoic acid and 4-hexylbenzoic acid had two absorption bands that appeared at similar frequencies and exhibited different vibration modes. This study interestingly demonstrates that even though compounds of an almost similar molecular structure might output bands at the same frequencies, the correspondence might not be apparent. The single molecule model frequencies and experimental frequencies for 4-decyloxybenzoic acid and 4-octyloxybenzoic acid further revealed that all the observed bands are due to intramolecular interaction. However, the 4-hexylbenzoic acid spectrum has one apparently intermolecular band. This work addresses the limitation in the intermediate terahertz spectroscopic studies of liquid crystals and furthermore emphasizes the robustness of Fourier Transform Infrared technique in identifying materials with similar attributes.

摘要

使用傅里叶变换红外方法对 4-辛氧基苯甲酸、4-癸氧基苯甲酸和 4-己基苯甲酸液晶进行太赫兹光谱研究。这些材料的特点是在 6-18 太赫兹频率范围内具有明显的吸收带。对于所有三种化合物，通过密度泛函理论计算获得的单分子的实验频率和理论频率之间观察到良好的对应关系。所研究化合物的光谱具有三个波段，它们出现在相似的频率和相同的振动模式。4-辛氧基苯甲酸、4-癸氧基苯甲酸和4-己基苯甲酸有两个吸收带，频率相似，振动模式不同。这项研究有趣地表明，即使分子结构几乎相似的化合物可能会以相同的频率输出波段，但对应关系可能并不明显。4-癸氧基苯甲酸和 4-辛氧基苯甲酸的单分子模型频率和实验频率进一步表明，所有观察到的条带都是由于分子内相互作用。然而，4-己基苯甲酸光谱有一个明显的分子间带。这项工作解决了液晶中间太赫兹光谱研究的局限性，并进一步强调了傅里叶变换红外技术在识别具有相似属性的材料方面的稳健性。4-癸氧基苯甲酸和 4-辛氧基苯甲酸的单分子模型频率和实验频率进一步表明，所有观察到的条带都是由于分子内相互作用。然而，4-己基苯甲酸光谱有一个明显的分子间带。这项工作解决了液晶中间太赫兹光谱研究的局限性，并进一步强调了傅里叶变换红外技术在识别具有相似属性的材料方面的稳健性。4-癸氧基苯甲酸和 4-辛氧基苯甲酸的单分子模型频率和实验频率进一步表明，所有观察到的条带都是由于分子内相互作用。然而，4-己基苯甲酸光谱有一个明显的分子间带。这项工作解决了液晶中间太赫兹光谱研究的局限性，并进一步强调了傅里叶变换红外技术在识别具有相似属性的材料方面的稳健性。