关键词: 有机电光晶体/
太赫兹光谱/
色散校正/
密度泛函理论
English Abstract
Terahertz spectrum study of organic electro-optic crystal 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium tosylate
Lian Yu-Xiang1,Dai Ze-Lin1,
Xu Xiang-Dong1,
Gu Yu1,
Li Xin-Rong1,
Wang Fu1,
Yang Chun2,
Cheng Xiao-Meng1,
Zhou Hua-Xin1
1.State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China(UESTC), Chengdu 610054, China;
2.College of Chemistry and Material Science, Sichuan Normal University, Chengdu 610068, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 61377063, 61421002, 61071032, 51172150).Received Date:28 June 2017
Accepted Date:25 July 2017
Published Online:05 December 2017
Abstract:The ground-state structural optimization and the terahertz spectrum calculation of an organic electro-optical crystal of 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) are performed using dispersion-corrected density functional theory (DFT-D2). DAST consists of an organic pyridinium salt (cation), one of the most efficient non-linear optical active chromophores and a sulfonate (anion) for enhancing the stability of the noncentrosymmetric macroscopic crystal. Such an organic crystalline salt DAST exhibits highly electro-optical and nonlinear optical coefficients, and it is an efficient emitter of THz pulses. The steady ground-state structure of DAST is obtained by a step-by-step optimization method with gradually increasing the convergence accuracy. The calculated terahertz spectra in 0-4 THz are in good agreement with experimental measurements, implying the reasonability of DFT-D2 method. Moreover, the vibration displacement vector diagrams for DAST molecular structure are obtained using Cambridge sequential total energy package animation simulation function. The results indicate that the phonon modes of DAST crystal at 1.12 THz are attributed to the optical phonon modes of the anion and cation, and DAST cation (organic pyridinium salt) and anion (sulfonate) undergo translational vibrations in their respective (benzene ring) plane. In contrast the vibrations at 1.46 THz and 1.54 THz are mainly related to the vibration of the sulfonate, among which 1.46 THz vibration is caused by the rotation of the sulfonate along the a axis, while 1.54 THz is due to the motion of the whole sulfonate along the c axis. And the vibrations at 2.63 THz and 3.16 THz originate from the torsional vibrations of cations and the rotation of anions, respectively. The results presented in this work clearly illustrate the contributions of the anion and cation of DAST in the THz responses. The mode assignments provide important reference and guidance for further synthesis of new DAST derivatives with larger electro-optical coefficients. In particular, our results suggest that DFT method is a powerful theoretical tool for studying the THz photonics and it is helpful not only for better understanding the mechanisms of the THz responses of organic electro-optic crystals, but also for controlling their performances.
Keywords: organic electro-optic crystal/
terahertz spectroscopy/
dispersion correction/
density functional theory
