Simulating terahertz absorption of fluorinated phenylacetylene biphenyl liquid crystal molecules

Abstract

Based on the density functional theory, ten kinds of fluoro-substituted liquid crystal derivative molecules, 4-butyl-4′-[(4-butylphenyl)acetylene]biphenyl, are simulated using Gaussian09 package with Opt+Freq optimization type and B3LYP/6-311g basis set. Comparing the substituted position and number of fluorine atoms, the absorption in terahertz region is discussed. Because substitution of fluorine atoms can significantly change the dipole moment of the molecule, the absorption in the low terahertz band is greatly affected by the substitutional position and number of fluorine atoms. For molecules with the same number of fluorine atoms, the different substitutional positions of the fluorine atoms bring about significant differences in the intensity and number of absorption peaks of the molecules. The location and number of the fluorine atom affect the absorption of functional groups in terahertz band. For instance, absorption of C-H bond in the benzene ring decreases due to the increase in the number of fluorine atoms in the benzene ring. The simulation result agrees well with the literature data on the absorption of molecular functional groups. Due to the measurement data of liquid crystal material absorption is lacking, we can only compare in the range of 0.3-3 THz. The results show that the calculation results have the same trend as the experimental measurement absorption curve of related literature. As a conclusion, our calculations can better reflect the absorption of molecular materials and provide effective suggestions for the design and synthesis of related molecules.