Synthesis and Physicochemical Investigation of THz Material: 4–Ethoxy Benzaldehyde–4'–N'–Methyl Stilbazolium Hexafluorophosphate (EMBSHP)

Abstract

Single crystals of organic optic material 4–Ethoxy Benzaldehyde–4'–N'–Methyl Stilbazolium Hexafluorophosphate (EMBSHP) were grown by slow evaporation technique at room temperature using acetone – water (3:1) mixed solvent. The grown crystal was subjected to single crystal X – ray diffraction analysis to identify the crystal structure and lattice parameter. The crystal belongs to the triclinic crystal system. The composition of the crystal was studied by CHN analysis. The presence of functional groups of the title crystal were confirmed from the FTIR spectral studies. The optical transmission range of the grown crystal was measured by UV – Vis – NIR spectral studies. The melting point of the grown crystal was found from DSC analysis. Introduction. Organic NLO materials with excellent optical characteristics such as high sensitivity and short response time have attracted much attention due to their potential applications in optical switching, optical processing, optical computing, optical data storage and terahertz (THZ) technology. Among the numerous organic materials, the well-known and most investigated organic NLO crystal is the stilbazolium salt trans-4-N-(dimethylamino)-N-Methyl-4-stilbazolium tosylate (DAST). It has very high electro optical (EO) and NLO figures of merit. Among all the other organic THz material, DAST has the largest NLO coefficient, d11 of 540 ± 110 pm/V at ~1540 nm, EO figure of merit r11=47 ± 8 pm/V at ~1535 nm and lower dielectric constant making it suitable for optoelectronic applications [1,2]. The advancement in the field of photonics have increased the demand for new nonlinear optical (NLO) materials. Especially, molecules exhibiting strong two photon absorption (TPA) are of practical importance in photons applications such as frequency up conversion lasing, three dimensional fluorescence imaging and multi photon microscopy ,eye and sensor protection, optical signal reshaping and stabilizing fast fluctuations of laser power. To expand these utilizing, designing the molecule with large TPA cross section plays a vital role [3]. DAST crystal can generate short THz pulse by optical rectification with a sub-picosecond laser [4, 5], or widely tunable THz waves by different frequency generation (DFG) with a dual wavelength nanosecond laser [6]. In this present study, the tosylate anion of DAST is replaced by Hexafluorophosphate (PF-6) and two methyl group along with nitrogen in the cation is replaced by ethoxy group for achieving the stilbazolium crystal 4-Ethoxy benzaldehyde 4'-N'-methyl stilbazolium Hexafluorophosphate (EMBSHP). The grown crystal has been subjected to single crystal XRD, CHN, FTIR, Optical absorption and thermal analysis.