烷基环己苯异硫氰酸液晶材料太赫兹波吸收

Terahertz wave absorption for alkylcyclohexylisothiocyanatobenzene liquid crystal materials

基于密度泛函理论,利用Gaussian09程序包,通过Opt+Freq优化结构,以B3LYP/6-311g基组对4-(trans-4-n-alkylcyclohexyl) isothiocyanatobenzenes (CHBT) 16种液晶分子在0.1—5.0 THz波段的吸收进行研究,提出了通过考察分子转动惯量和质量重心偏移对太赫兹吸收的影响方法.计算结果表明,随着分子烷基链上碳原子数目增加,分子的转动惯量和重心的偏移将对太赫兹波的吸收产生影响.在0.1—5.0 THz波段, 3—7个碳原子的分子吸收相对较强.以此为参照,减少和增加烷基链上的碳原子数目都会降低分子对太赫兹波的吸收.在0.3—3.0 THz范围内,将计算结果与10种有实验数据的分子进行了对比.结果发现,低频波段计算结果与实验测量相比存在差异,其中吸收峰位置的差异可能来源于氢键.比较吸收强度的相对大小值,发现实验测量与计算结果较为一致,表明吸收强度来源于偶极子振动、转动吸收,展现了计算模拟的积极意义.研究结果可对相关分子的设计与合成提供有用的建议.

According to density functional theory,in this paper we report a simulation result obtained by using the Gaussian09 package.Adopted in the calculation are an optimized Opt Freq and a base group of B3 LYP/6-311 g to simulate the absorption of 16 kinds of liquid crystal(LC)molecules of 4-(trans-4-n-alkylcyclohexyl)isothiocyanatobenzenes(CHBT)in a 0.1-5.0 terahertz band(THz).The results show that in the low terahertz band,the absorption is caused mainly by the vibration and rotation of the molecules.So for convenience,we present an novel analytical method of studying the influence of molecular moment of inertia and mass center of gravity shift on absorption.An important result is found that the length of the molecular alkyl chain can lead to different molecular mass,mass center of gravity and moment of inertia,which causes the rotation and vibration of the molecule to be different.These factors lead to the difference in terahertz wave absorption.In the 0.1-5.0 terahertz band,the molecules with 3-7 alkyl chain carbon atoms show a strong absorption.As a reference,reducing and increasing the carbon atoms in the alkyl chain will cause the molecules to reduce the absorption of terahertz waves.In the end,the calculated results are compared with the experimental results obtained from 10 molecules according to the reference data in a frequency range of 0.3-3.0 terahertz.It is found that in the low frequency band there exist some differences between the calculation results and the experimental measurements,in which the difference in the position of the absorption peak may originate from a hydrogen bond.Comparing the relative magnitudes of the absorption intensities,it is found that the experimental measurements are consistent with the calculated results,indicating that the absorption intensity comes from the absorption of dipole vibration and rotation,which demonstrates the positive significance of computational simulation.We look forward to the experimental measurements in the future,and correct the calculation methods and keywords as well as the parameters such as temperature calculation that is to be done in future work.As a theoretical basis,the calculation results can better reflect the absorption of molecular materials,and it is expected to provide useful suggestions for designing and synthesizing the liquid crystal molecules.