Stilbazolium Tosylate Research Articles

Exploring the influence of CdCl2 on the nonlinear properties of 4–N, N–dimethylamino – 4–N–methyl – stilbazolium tosylate (DAST) crystal for optoelectronic applications

ABSTRACT This article describes the enhancement of optical and NLO properties of a novel cadmium chloride doped DAST organic single crystals, which have been effectively grown by slow evaporation technique. The as-prepared crystals were inspected by various experimental characterisation such as SXRD and PXRD, FT-IR, UV–Vis–NIR, EDAX, and SHG analysis. The structural analysis and elemental analysis confirmed the incorporation of dopant materials and their effect on the structural aspects. The optical studies of the pure and doped crystals showing the desirable changes in the cut-off wavelengths, mostly affected by n – π* electronic transition in this case. Interestingly, the SHG efficiencies of the Cd doped DAST crystals were enhanced to be 1.29, 1.41 and 1.79 times greater than pure DAST crystal. The estimated optical parameters and the efficient SHG efficiency of Cd doped DAST single crystal reveals that they could be prominent materials for optoelectronic and nonlinear optical (NLO) applications.

(Invited) Mechanistic Studies for Electrochemical Self-Assembly of Cuscn/Stilbazolium Dye Hybrid Thin Films

We have established electrochemical self-assembly (ESA) of inorganic / organic hybrid thin films in which the inorganic is CuSCN, known as a wide bandgap p-type semiconductor, whereas the organic is 4-N,N-dimethylamino-4’-N’-methylstilbazolium chromophore (abbreviated as DAS+) as its salt with tosylate (DAST) known to exhibit second-order nonlinear optical property for terahertz emitters. The CuSCN/DAS hybrid thin films by ESA show concerted photoluminescence based on energy transfer from inorganic CuSCN to organic DAS, making us anticipate its potential use in optoelectronic devices [1]. Understanding the mechanism of ESA to obtain tuning knob to maximize its functionality is therefore important.In our previous study, switching of dye loading mechanism has been suggested, depending on DAS concentration (C DAS) in the bath [2]. With low C DAS, the loading is limited by diffusion so that DAS is entrapped within CuSCN crystal grains, while surface reaction of hybridization begins to limit the dye loading with high C DAS, resulting in formation of unique nanostructures as well as phase separation of inorganic and organic domains. The border for the switching of dye loading mechanism was found as the ratio between bulk concentrations of dye and the [Cu(SCN)]+ complex, C DAS/C comp = ca. 1/31 in case of DAS+ [3].In this study, electrochemical analysis has been performed employing rotating disk electrode (RDE) under variation of bulk concentration of dye (DAST and CNST = 4-cyano-4’-(N’-methyl)stilbazolium tosylate for comparison) to verify the proposed mechanism. CNS+ has a strongly electron withdrawing -CN group and therefore bears a much larger dipole moment of 23.5016 Debye than that of DAS+ (10.1442 Debye) as determined by DFT calculation. Thus, a much stronger interaction of CNS+ with CuSCN (essentially with SCN- ion) is expected than DAS+.The overall behavior of CNS+ has been found exactly the same as DAS+ such as changing the crystal orientation of β-CuSCN to lay down its c-axis and phase transition from β- to α-CuSCN. However, such transitions were found for smaller concentrations of CNS+ than DAS+ because of its stronger affinity with CuSCN. The switching dye loading mechanism and associated change of the hybrid structure has also been observed for CNS. Fig. 1 shows plots of amount of dye loaded into the hybrid thin films against the dye concentrations in the electrolytic bath for DAS+ and CNS+. The steep slopes in low dye concentration range represent diffusion limited loading, whereas the moderate slopes are those limited by surface reaction. The bending points, C DAS = 60 μmol dm-3 and C CNS = 200 μmol dm-3, indicate the switching borders for C comp = 2.5 mM. Because of the increased stability of adsorption of CNS+ on CuSCN surface, diffusion limited loading, thus all dyes reaching the electrode surface buried inside the film, continues to operate up to this high dye concentration. The increased stability of CuSCN/CNS surface complex also resulted in about 3 times more efficient dye uptake in the surface reaction limited regime. These results nicely confirm the validity of the proposed mechanism both for DAS+ and CNS+, and that the switching border can be varied by the stability of CuSCN/dye complex. Full analysis should be able to determine C CNS/C comp ratio as the switching border.[1] K. Uda et al. ACS Omega, 4, 4056-4062 (2019).[2] Y. Tsuda et al., Monatshefte für Chemie, 148, 845-854 (2017).[3] Y. Tsuda et al., J. Electrochem. Soc. 166(9) B3096-B3102 (2019). Figure 1

Thin-Film Nonlinear Optical Crystals for Intracavity Electro-Optic Modulation

Methods of preparation of single-crystal 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST) films with a thickness of several micrometers, designed for electro-optic modulation, have been analyzed. Thin-film single crystals have been obtained, the shape and absorption spectrum of which confirm their crystal structure of the “red” DAST crystal form. Homogeneous luminescence in the polarization-contrast regime indicates their single crystallinity and uniform orientation. These materials are designed for intracavity modulation of laser radiation.

Nonlinear optical process of second-order nonlinear optical susceptibility χ133(2) in an organic nonlinear optical crystal DAST.

A large unexamined second-order nonlinear optical (NLO) process is found in a 4-N,N-dimethylamino-4'-N'-methyl stilbazolium tosylate (DAST) crystal, which has a large figure of merit among NLO crystals. In second-order NLO processes using a DAST crystal, the χ111(2) process of light excitation is commonly used, involving a-axis polarized light excitation with light generation of a-axis polarized light. However, there have been few studies of other second-order NLO susceptibility processes to date. In this Letter, terahertz (THz) wave generation via second-order NLO processes based on the χ133(2) second-order NLO susceptibility of the DAST crystal was investigated. By adjusting the polarization direction of the excitation light using a prism-coupled Cerenkov phase-matching method, efficient generation of THz waves was achieved using a process involving χ133(2). The magnitude of the NLO constant χ133(2) estimated from the THz intensity ratio was 77.8 pm/V. These results indicate that prism-coupled Cherenkov phase matching can be used to identify undiscovered NLO processes for NLO crystals.

Bulk crystal growth and characterization of 3-HBST: A promising organic nonlinear optical crystal with high quality

High yield 3-hydroxy benzaldehyde-N-methyl 4-stilbazolium tosylate (3-HBST) was synthesized by optimizing the reaction temperature. High-quality bulk crystals of 3-HBST were grown by slow evaporation technique and spontaneous nucleation method, respectively. The crystal structure of 3-HBST was determined by single crystal X-ray diffraction (XRD) technique and belongs to monoclinic system. The defects of the 3-HBST crystals were observed by the synchrotron radiation X-ray topography. 3-HBST crystal remains stable until 305 °C, with a melting point of 214.1 °C from the TG-DTG and DSC techniques. The dielectric constant of 3-HBST crystal was also studied. The grown crystal had good optical transparency and the optical transmittance was investigated by UV-vis-NIR spectral analysis. Photoluminescence (PL) indicated green emission occurred at 478 nm. Based on the growth technical analysis and performance parameters measurements, 3-HBST crystal was verified to be a promising organic nonlinear optical crystal.

Optical and biological characteristics of novel organic single crystal 4-chloro N-methyl 4-stilbazolium tosylate

When compared with inorganic materials, the molecular organic materials acquire significant interest because of their considerable nonlinear optical properties, virtual unlimited design possibilities and extremely fast response times. Amongst them, organic crystals which are based on the charged chromophores and substantial Coulomb interaction have a number of benefits over non-ionic species, like first-order hyperpolarizability or greater molecular nonlinearity, durable stability and having a larger capability to override the dipole–dipole interactions and therefore it forms a non-centro symmetric macroscopic packing. For instance, DAST (4-N, N-dimethylamino-4′-N′-methyl-stilbazolium tosylate), the organic salt crystal, is one of the finest nonlinear optical materials having larger second-order nonlinear optical susceptibilities. Even though benchmark stilbazolium crystals display a great macroscopic nonlinearity and noble crystal characteristics, improving these physical properties comprising the environmental stability is a provocative topic. Based on this, the present paper discusses the growth of cationic substituted DAST namely 4-chloro -N-methyl 4-stilbazolium tosylate (CMST). Knoevenagel reaction method was used to synthesis CMST salt using Dean-Stark apparatus. The synthesized salt of CMST was dried at 100 °C for 24 h. The dried CMST salt was used to grow the crystals after three recrystallization process. Based on the solubility curve new solvent, mixture of methanol and acetonitrile was used to grow the crystals at room temperature by slope nucleation method. Structure of the grown crystals was characterized using single crystal XRD and FTIR. The compositional analysis was carried out using NMR and CHN analysis. Luminescence characteristics was studied using photoluminescence spectrum. The dielectric characteristics ware carried out from room temperature to 250 °C. Invitro analysis was carried out in the cancer cell line to study it’s anti-cancer activity.

Тонкопленочные нелинейно-оптические кристаллы для внутрирезонаторной электрооптической модуляции

Methods for the preparation of DAST (4-N, N – dimethylamino–4'-N'-methyl stilbazolium tosylate) thin monocrystals with a thickness of a few micrometers, intended for electro-optics modulation were investigated. Thin-film single crystals are obtained, the shape and absorption spectrum of which confirms their crystalline structure of the “red” form DAST. Uniform color in the polarization contrast mode shows their monocrystallinity and uniform orientation. The materials are intended for intracavity modulation of laser radiation.

Growth and characterization of organic 4-chlorobenzaldehyde-N- methyl 4-stilbazolium tosylate crystal: A promising material for nonlinear optical device applications

The organic crystal 4-chlorobenzaldehyde-N-methyl 4-stilbazolium tosylate (CMST) was grown from acetonitrile and methanol mixed solvent using slow cooling method for the first time. The optimum growth conditions based on different solution concentrations were investigated. The crystal atomic packing and bond length alternation (BLA) of CMST were identified through single crystal X-ray diffraction analysis, the calculated BLA value 0.1475 Å is close to optimum value for nonlinear optical (NLO) response. The composition and different functional groups of CMST compound were determined by 1H NMR and FT-IR studies. Moreover, the thermal stability and melting point were obtained through TG/DTG and DSC analyses. Important optical parameters such as optical transmittance, cut-off wavelength, absorption coefficient, band gap energy and refractive index were ascertained through UV–vis-NIR study, the low cut-off wavelength and wide optical transmittance of CMST crystal are favorable to optical device fabrication. The dielectric constant has been investigated. Green emission occurred at 521 nm was found through photoluminescence excitation study. These encouraging results suggest that the CMST crystal is a promising candidate for nonlinear optical device applications.

Study of optical and laser damage threshold in EDTA and DTPA-doped DAST single crystals

We report the influence of EDTA and DTPA on the optical and laser damage thresholds of industrially relevant 4-dimethylamino-N-methyl stilbazolium tosylate (DAST) single crystals. Single crystal X-ray diffraction and powder X-ray diffraction studies substantiate that they crystallize in monoclinic system. The dopants facilitate tuning of the refractive indices and their optical conductivity. The laser damage threshold values of EDTA and DTPA-doped DAST crystals were found to be 1.5 and 1.6 times higher than the pure DAST crystal. The voltage-dependant photoconducting studies performed at ambient conditions shows negative photoconducting nature for pure and EDTA-doped DAST crystals while positive photoconducting nature is noticed for DTPA-doped crystal. The etching studies demonstrate the quality of the doped DAST crystals is better than the pure one.

Investigation on the Growth, Structural and Third Order Nonlinear Optical Properties of 4-Ethoxy-4-N-Methyl-4-Stilbazoliumhexafluorophosphate (EMSHP) Single Crystal

The organic material 4-ethoxy-4-N-methyl-4-stilbazolium hexafluorophosphate (EMSHP) is a new NLO material and new derivative in stilbazolium tosylate family. In this work we synthesized EMSHP, the derivative of DAST, by slow evaporation method. The chromophores of the EMSHP crystal makes an angle of about 28 with repeat to a- axis which makes this material a promising terahertz (THz) wave generation and used for various electro – optic applications. The crystal system is found as monoclinic. From the UV–Vis NIR absorption spectra the good transparency is revealed. The indication at 498 nm of the crystal ascertains the blue to green emission was validated by using photo luminescence (PL) analysis. The third-order nonlinear optical properties such as nonlinear refractive index (n 2 ), absorption co-efficient (β) and susceptibility (χ (3) ) were studied by Z-scan technique at 632.8 nm using He-Ne laser. All the above studies supports the as grown EMSHP crystal is a suitable candidate for generation of THz and opto- electronic application.

Growth, structural, thermal, dielectric and optical studies on HBST crystal: A potential THz emitter

The efficient organic nonlinear optical material 4-hydroxy benzaldehyde-N-methyl 4-stilbazolium tosylate (HBST) was grown from methanol by slope nucleation method combined with slow cooling (SNM-SC) for the first time. The optimum growth conditions based on the cooling rate was further investigated. The single crystal X-ray diffraction (XRD) revealed that the chromophores of HBST crystal make an angle of about 33° with respect to the a-axis, which is close to the optimum of Terahertz (THz)-wave generation and electro-optics applications. NMR and FT-IR spectral studies have been performed to ascertain various functional groups present in the sample. Futhermore, the thermal stability and decomposition stages were analyzed through TG-DTA and DSC techniques. The dielectric constant and dielectric loss of HBST crystal have been studied. Critical optical properties like the absorption coefficient, refractive index, cut-off wavelength and band gap energy were calculated. Photoluminescence (PL) exication studies indicated green emission occured at 507nm. All the results of HBST crystal make it a promising candidate in the fields of optoelectronic and the generation of THz.

The research progress on organic nonlinear optical crystal DAST and its application in Teraherz region

This article mainly introduces the basic structure and physical performance parameters , several kinds of growth methods about 4- N , N -dimethylamino-4- N -methyl stilbazolium tosylate (DAST) crystal, and generating THz wave based on DAST crystal by optical difference frequency method. The dual wavelength tuning range and beam quality of optical pump sources have an important impact on the conversion efficiency and tuning range of THz in the generation of THz radiation based on DAST crystal by the optical difference frequency (DFG). In addition, the influences of optical pump (the wavelength of femtosecond laser, pulse width and energy) to the THz pulse output enengy and conversion efficiency in the process of generating THz using optical rectification (OR) were also reported. The influence factors of THz radiation and main challenges in the process of growing high quality and large size DAST crystal have been analyzed comprehensively. Bulk single crystal were grown with dimensions of 25 mm×22 mm×2 mm using the slope nucleation coupled with seed crystal method in our present work on systematic analyzing the advantages and disadvantages of spontaneous nucleation method, slope nucleation method, seed crystal method and two zone growth method. Next, we expect to improve laser-THz conversion efficiency and the THz radiation energy by optimizing the process of crystal growth and improving the quality of optical pump.

Generation of single-cycle terahertz pulse using Cherenkov phase matching with 4-dimethylamino-N′-methyl-4′-stilbazolium tosylate crystal

This is the first report of single-cycle terahertz (THz)-wave pulse generation with a wide band (over 6 THz) and a high dynamic range (over 70 dB) using an organic nonlinear optical crystal, 4-dimethylamino-N′-methyl-4′-stilbazolium tosylate (DAST), and the prism-coupled Cherenkov phase-matching method. The prism-coupled approach allowed the use of a DAST crystal as a Cherenkov-type emitter for reduced light absorption by the crystal, resulting in the generation of single- and half-cycle THz pulse shapes, which were detected using dipole and bow-tie antennas, respectively. The resulting THz pulse generation is suitable for various THz-wave application technologies, such as tomography.

Electrochemical self-assembly of CuSCN-DAST hybrid thin films

Nanostructured inorganic–organic hybrid thin films of copper(I) thiocyanate (CuSCN) and 4-(N,N-dimethylamino)-4′-(N′-methyl)stilbazolium tosylate (DAST) were electrochemically self-assembled by adding DAST into methanolic bath containing Cu2+ and SCN− ions. Loading of the stilbazolium organic chromophore (DAS+) increased linearly on increasing DAST concentration, accompanied with changes of the film morphology, crystallographic orientation of CuSCN and transition from β- to α-CuSCN. At low DAST concentrations, transport limited passive occlusion of DAS+ has been suggested with its diffusion coefficient of 1.25 × 10−6 cm2 s−1 in methanol at 298 K, while the loading receives kinetic limitation by the surface chemical reaction to yield definitive hybrid structures, resulting in unique “hair comb” shape β-CuSCN-DAST and “nano-platelets” shape α-CuSCN-DAST hybrid structures. Both the inorganic and organic components are interconnected and bi-continuous, as the loaded DAS+ could be totally extracted by dimethylacetamide to leave porous skeleton of crystalline CuSCN, making them highly interesting for device applications.

Growth and characterization of DAST crystal with large-thickness

Highly nonlinear optical 4-N, N-dimethylamino-4-N-methyl stilbazolium tosylate (DAST) crystals with large surface and thickness was grown by the slope nucleation technology with slow-cooling in a high concentration solution. The structure and composition of the crystal were confirmed by X-ray diffraction (XRD). The surface morphology of the crystal was characterized by optical microscope. Growth layers were observed on the (001) surface and several isolated “island layers” were also found. The mechanism of crystal growth was analyzed. Etching behavior of the (001) and (001¯) faces of the crystal was studied with methanol, respectively. Optical properties of the crystal were also characterized by UV–vis–NIR spectrometer. The dielectric constants and the dielectric loss were tested by impedance analyzer.

Temperature Dependence of Crystal Structure and THz Absorption Spectra of Organic Nonlinear Optical Stilbazolium Material for High-Output THz-Wave Generation

A stilbazolium material comprising 4-dimethylamino-N′-methyl-4′-stilbazolium tosylate (DAST), which has a large nonlinear optical susceptibility, was studied for application in terahertz (THz)-wave generation. The temperature-dependent structure of the DAST crystal was measured by using powder X-ray diffraction from −100 to 200 °C, indicating a volume expansion of 4.6 %. The lattice constants show anisotropic thermal expansion. Also, the temperature dependence of THz absorption spectra was measured by terahertz time-domain spectroscopy (THz-TDS) in the temperature range varying from −80 to 88.1 °C. A strong absorption peak was found at around 1 THz, shifting slightly toward a lower frequency with increasing temperature. The temperature dependence of the THz spectra was compared with that of X-ray diffraction. The shifting of THz-vibrational frequencies of the DAST crystal suggests that the change in its lattice structure is temperature dependent.

Influence of organic dopants on the optical properties of 4-N,N′-dimethylamino-N′-methyl stilbazolium tosylate crystals

Organic crystals of 4-N,N′-dimethylamino-N′-methyl stilbazolium tosylate (DAST), 2-amino-5-nitro pyridinium (2A5NP) and 2-amino-5-nitro pyridine toluene sulfonate (2A5NPTS) doped DAST crystals were grown by slow cooling method. The powder samples were examined by X-ray diffraction to estimate the lattice parameter values of the crystals. Fourier Transform Infra-Red (FT-IR) and Fourier Transform-Raman (FT-Raman) spectroscopic studies were performed to identify the various functional groups associated with the crystals. The four strong vibrational modes were observed at 1161cm−1, 1181cm−1, 1346cm−1 and 1577cm−1 contributing to linear electro-optic effect in DAST crystals. The Density Functional Theory (DFT) was used for FT-IR and FT-Raman analysis by means of the hybrid functional DFT/B3LYP with 6-311 G (d, p) basis set. The optical band-gaps were calculated from the UV–vis and photoluminescence spectra of pure and doped DAST samples.

Growth and characterization of novel organic 3-Hydroxy Benzaldehyde-N-methyl 4 Stilbazolium Tosylate crystals for NLO applications

The 3-Hydroxy Benzaldehyde-N-methyl 4-Stilbazolium Tosylate (3- HBST) is a new organic NLO crystal and it is a new derivative in stilbazolium tosylate family. In this work we have synthesized 3-HBST and the single crystal was grown by conventional slow cooling method. The structure and lattice parameters of the grown crystal were determined by the single crystal X-ray diffraction (XRD) technique and it is exhibiting good crystalline nature which is observed from the powder XRD. In order to check the crystalline quality the rocking curve was recorded using multi crystal X-ray diffractometer. The functional groups were identified from both FTIR and NMR spectral analyses. The π–π* and n–π* optical transition energy levels were estimated from the absorption peaks. The NLO property was confirmed by measuring relative SHG efficiency by Kurtz powder test; it shows 24 times higher SHG efficiency than that of urea. In order to test the mechanical stability the Vickers and Knoop micro hardness measurement were carried out and found that the micro hardness number decreases with increasing load. The melting point was determined from Differential Scanning Colorimetry (DSC).

Diffraction-limited real-time terahertz imaging by optical frequency up-conversion in a DAST crystal.

Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and the arts. This report describes real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in an organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate (DAST) crystal, with high resolution reaching the diffraction limit. THz-wave images were converted to the near infrared region and then captured using an InGaAs camera in a tandem imaging system. The resolution of the imaging system was analyzed. Diffraction and interference of THz wave were observed in the experiments. Videos are supplied to show the interference pattern variation that occurs with sample moving and tilting.

Growth and defects of DAST crystal in high concentration solution

The 4-N,N-dimethylamino-4-N-methyl stilbazolium tosylate (DAST) crystal with large size and nearly square shape was grown in high concentration solution by slope nucleation method coupled slow cooling (SNM-SC). Striations considered as planar defects were found on the (001) face along a-axis in the crystal by optical microscope. Some of the striations were continuous while some of them were discontinuous. In addition, the striations were found on (231) diffracting face and such lines did not occur on the (3-21) and (−221) planes. The surface distribution and morphological structure of the crystal were characterized by XRD and atomic force microscope (AFM). The presence of striations in the sample was also confirmed by white-beam synchrotron radiation topography (WBSRT). The mechanism of striations formation was also discussed.