Hindawi Publishing Corporation Indian Journal of Materials Science Volume 2013, Article ID 680256, 4 pages http://dx.doi.org/10.1155/2013/680256
Research Article Crystal Growth and Characterization of a New NLO Material: p-Toluidine p-Toluenesulfonate M. Suresh,1 S. Asath Bahadur,2 and S. Athimoolam3 1
Department of Physics, Er. Perumal Manimekalai College of Engineering, Hosur, Tamil Nadu 635 11, India Department of Physics, Kalasalingam University, Krishnakoil, Tamil Nadu 626 190, India 3 Department of Physics, Anna University, Tirunelveli Region, Nagercoil, Tamil Nadu 629 004, India 2
Correspondence should be addressed to M. Suresh;
[email protected] Received 5 September 2013; Accepted 5 November 2013 Academic Editors: K. M. Garadkar and A. Kajbafvala Copyright © 2013 M. Suresh et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Single crystals of p-Toluidine p-Toluenesulfonate (PTPT), an organic nonlinear optical (NLO) material, have been grown by slow evaporation method at room temperature using ethanol as solvent. The crystal system was confirmed from the single crystal X-ray diffraction analysis. The functional groups were identified using FTIR spectroscopy. UV-Vis-NIR spectrum showed that the UV cut-off wavelength of PTPT occurs at 295 nm and it has insignificant absorption in the wavelength region of 532–800 nm. The SHG efficiency of PTPT was measured by employing Kurtz and Perry powder technique using a Q-switched mode locked Nd: YAG laser emitting 1064 nm for the first time and it was found to be 52% of standard KDP. Thermal and mechanical properties of PTPT were examined by TG/DTA and Vickers microhardness test, respectively.
1. Introduction Materials with large nonlinear optical susceptibilities are of current interest in the area of harmonic generation and optical modulation. In recent years, some polar organic crystals, which form a noncentrosymmetric structure which exhibit second-order nonlinear optical properties that far surpassed those of the conventional materials, have led to the synthesis and evaluation of a wide range of potentially useful solids [1]. Materials showing high optical nonlinearity have potential applications in signal transmission, data storage, optical switching, laser printing, displays, inflorescence, photolithography, remote sensing, chemical and biological species detection, high resolution spectroscopy, medical diagnosis, and underwater monitoring and communication [2]. Different types of molecular and bulk materials have been examined for nonlinear optical properties. Organic nonlinear materials are attracting a great deal of attention, as they have large optical susceptibilities, inherent ultrafast response times, and high optical thresholds for laser power as compared with inorganic materials [3]. Organic molecules with significant nonlinear optical activity generally consist
of a 𝜋-electron conjugated structure. The conjugated 𝜋electron moiety provides a pathway for the entire length of conjugation under the perturbation of an external electric field. Fictionalization of both ends of the 𝜋-bond systems with appropriate electron donor and acceptor group can increase the asymmetric electronic distribution in either or both the ground and excited states, thus leading to an increased optical nonlinearity [4–7]. In the present investigation, we report the growth and characterization especially the SHG efficiency of p-Toluidine p-Toluenesulfonate (PTPT) for the first time. The grown crystals have been subjected to the characterizations like XRD, FTIR, UV-vis, thermal analysis, powder SHG, and microhardness studies.
2. Material and Methods 2.1. Crystal Growth. The title compound was obtained by the addition of p-toluenesulfonic acid (0.02 mol) to a solution of p-Toluidine (0.02 mol) in ethanol, in the stoichiometric ratio 1 : 1. Within a week, tiny crystals were formed due to the spontaneous nucleation. Optically transparent good quality
2
Indian Journal of Materials Science Table 1: FTIR spectral data of PTPT.
Figure 1: Grown Crystal of PTPT. NH3
+
SO3
−
·
CH3
CH3
S. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Wave number (cm−1 ) 3324b 2677m 1694s 1694s 1576m 1502v 1448m 1295m 1192m 1156s 1091w 936s 856s 769b & 743b 664w 621w & 575w 769m 700w 559s 525m 452w
Tentative assignments NH3 + Asymmetric Str NH− Str + NH3 Asymmetric Str SO3 − Asymmetric bending NH3 + Asymmetric deformation Ring Str NH3 + Asymmetric bending C–H bending in plane H bond C–H bending SO3 − Symmetric Str C–H in plane deformation C–C str/SO− Antisymmetric str CH− deformation N–H deformation C–C str N–H deformation C–C str COO− deformation C–C deformation C–C deformation
Figure 2: Molecular Structure of PTPT.
crystals were used as seeds for further growth experiments. For growth, seed crystals were just immersed into the prepared solution. Good quality crystals with characteristic shape and size of 10 × 5 × 2 mm3 were obtained for 10 days. Figures 1 and 2 show the photograph of the grown crystals and molecular structure of PTPT, respectively. 2.2. Characterization. In order to confirm the grown crystal, single crystal 𝑋-ray diffraction studies were carried out using ENRAF NONIUS CAD4-F single 𝑋-ray diffractometer with ˚ radiation. The FTIR spectrum MoK𝛼 (𝜆 = 0.71073 A) of the sample was recorded in the range 4000–450 cm−1 using Jasco Spectrometer (FTIR, model 410) by KBr pellet technique. The UV-Vis-NIR analysis was carried out between 200 and 800 nm covering the entire ultraviolet, visible, and near infrared regions using the UV-1700 Shimadzu spectrometer. Vicker’s microhardness tester was used to assess the mechanical properties of the grown crystal for various loads ranging from 25 to 100 g. The thermal behavior of the grown crystal was studied using simultaneous TG/DTA in the temperature range of 20∘ C–600∘ C analyses using SEIKO TG/DTA6200 analyzer in nitrogen atmosphere at the heating rate of 20∘ C/min. The SHG efficiency was measured by employing Kurtz and Perry powder technique using a Qswitched mode locked Nd: YAG laser emitting 1064 nm.
3. Results and Discussion 3.1. Single Crystal XRD Studies. Using the single crystal 𝑋ray diffraction analysis, the cell parameters of PTPT were
obtained from least-squares refinement of the setting angles of 25 reflections. The XRD study reveals that the crystal belongs to monoclinic system with lattice parameters of 𝑎 = ˚ 𝑏 = 9.010(8) A ˚ and 𝑐 = 13.320(7) A, ˚ 𝑍 = 2, 5.778(6) A, and space group is P21 , which is in agreement with those of reported values [8]. 3.2. Density Measurement. The density of the crystal was determined by the floatation technique (also called the sink or swim technique). For the measurement of crystal density, carbon tetrachloride of density 1.59 gm/cm3 was used as denser liquid and xylene of density 0.89 gm/cm3 was used as lower density liquid. The density of the single crystal of title compound was determined as 1.341(1) gm/cm3 using this floatation technique and the theoretically expected density is 1.298 gm/cm3 . 3.3. FTIR Analysis. The FTIR spectrum recorder for the PTPT is shown in Figure 3 and its tentative assignments of vibrational frequencies are given in the Table 1. 3.4. UV-Vis-NIR Studies. To analyze the optical properties of grown PTPT crystal, UV-Vis transmittance was recorded. For this, polished sample of 1 mm thick from the grown crystal was used. The recorded UV-Vis-NIR spectrum of PTPT is shown in Figure 4. The optical absorption study shows that the UV cut-off wavelength of PTPT occurs at 295 nm. It is well known that the efficient NLO crystal has an optical transparency at lower cut-off wavelength between 200 and 400 nm [9]. There is no significant absorption in the entire visible region which reveals that it can find applications in the
Indian Journal of Materials Science
3
110 100
50 4000
3000
856.23
769.45 743.42
936.27
664.35 621.93 525.50
1192.96 1091.51 1156.12
2000
1295.93
1694.16
60
1504.2 1448.28
1576.52
2677.68
2884.02
70
3324.68
3618.77
80
3843.43 3742.19
T (%)
90
1000
Wavenumber (cm−1 )
Figure 3: FTIR Spectrum of PTPT.
264
10.00
0.4
5.00
0.3
96%
TG (%)
0.5
0.00 −5.00
295 0.2
−10.00 0.1
100
202.3 ∘ C 200
320.3 ∘ C 300
400.0
500
Temperature (∘ C)
530
0.0
100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 600
547.9∘ C
15.00
DTA
Absorbtion (a.u.)
0.6
Figure 5: TGA/DTA Curve of PTPT. 100
200
300
400 500 600 700 Wavelength (nm)
800
900
1000
Figure 4: UV-Vis-NIR Spectrum of PTPT.
optoelectronic devices. Also, the very low absorption around 532 nm signifies the resistance of the grown crystal to laser induced damage [10]. 3.5. Thermal Studies. TGA/DTA curve of PTPT is given in Figure 5. The DTA curve of PTPT indicates that the material has two sharp exothermic peaks at 202.3∘ C and 320.3∘ C, which represent the melting and decomposition points, respectively. The TGA curve of PTPT indicates that the sample is stable from ambient up to 202∘ C. The major weight loss between 202 and 320∘ C is due to the decomposition. The total weight loss of the sample is 96% at 320∘ C. 3.6. Microhardness Studies. Hardness is one of the important mechanical properties to determine the plastic nature and strength of a material. The well polished PTPT crystal was placed on the platform of the Vicker’s microhardness tester and the loads of different magnitudes were applied over a fixed interval of time. The hardness number was calculated using the relation 𝐻V = (1.8544𝑃)/(𝑑2 ) kg/mm2 , where 𝑃
is the applied load in kg and 𝑑 is the diagonal length of the indentation impression in micrometer. The relation between hardness number (𝐻V ) and load (𝑃) for PTPT is shown in Figure 6. The hardness increases gradually with the increase in load and above 100 g cracks were developed on the plane of the crystal due to the release of internal stresses generated locally by indentation. Meyer’s index 𝑛 was calculated from the graph (Figure 7) plotted against log 𝑃 versus log 𝑑. The slope of the line obtained from graph predicts that the value of 𝑛 is greater than 2. 𝐻V should increase with the increase of 𝑃 if 𝑛 > 2 and decrease if 𝑛 < 2 [11]. Thus, the 𝑛 value satisfies the observed result. 3.7. Second Harmonic Generation. Since PTPT has crystallized in a noncentrosymmetric space group, a preliminary study of the powder SHG conversion efficiency was carried. A Q-switched Nd: YAG laser beam of 1064 nm wavelength was used with an input power of 4.4 mJ pulse−1 , pulse width of 10 ns, and the repetition rate of 10 Hz. The crystals of PTPT were ground to a uniform particle size of about 125–150 𝜇m and then packed in capillaries of uniform bore and exposed to the laser radiation. A powder of potassium dihydrogen orthophosphate (KDP), with the same particle size, was used as the reference. The output from the sample was
4
Indian Journal of Materials Science
Acknowledgments
Hardness number (kg/mm2 )
95
The authors thank Dr. P. K. Das, IISc Bangalore, for providing SHG testing facilities.
90 85
References
80 75 70 65 20
30
40
50
60
70
80
90
100
110
Load P (g)
Figure 6: (𝐻V ) versus load (𝑃).
2.0 1.9
Log P
1.8 1.7 1.6 1.5 1.4 1.3 1.80 1.82 1.84 1.86 1.88 1.90 1.92 1.94 1.96 1.98 Log d
Figure 7: log 𝑃 versus log 𝑑.
monochromated to collect only the second harmonic (𝜆 = 532 nm) eliminating the fundamental, and the intensity was measured using a photomultiplier tube. Second harmonic signal of 5.58 mV was obtained. The standard KDP crystals gave a SHG signal of 11 mV for the same input energy. From this measurement, it is found that the SHG efficiency of PTPT is 52% of standard KDP.
4. Conclusion Single crystals of p-Toluidine p-Toluenesulfonate (PTPT) were grown from ethanol solution by slow evaporation of the solvent at room temperature. The crystal system was confirmed from the single crystal 𝑋-ray diffraction analysis. The functional groups of the compound were determined from FTIR spectrum. Optical absorption studies show that the sample has minimum absorption in the entire visible region. The melting point of PTPT was found to be 202.3∘ C from the DTA curve. The SHG efficiency of PTPT was found to be 0.52 times than that of standard KDP.
[1] P. N. Prasad and D. J. Williams, Introduction to Nonlinear Optical Effects in Organic Molecules and Polymers, John Wiley & Sons, New York, NY, USA, 1991. [2] D. S. Chemla and J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, New York, NY, USA, 1987. [3] T. Pal, T. Kar, G. Bocelli, and L. Rigi, “Synthesis, growth, and characterization of L-arginine acetate crystal: a potential NLO material,” Crystal Growth and Design, vol. 3, no. 1, pp. 13–16, 2003. [4] R. T. Bailey, G. Bourhill, F. R. Cruickshank, D. Pugh, J. N. Sherwood, and G. S. Simpson, “The linear and nonlinear optical properties of the organic nonlinear material 4-nitro-4’methylbenzylidene aniline,” Journal of Applied Physics, vol. 73, no. 4, pp. 1591–1597, 1993. [5] C. K. Lakshmana Perumal, A. Arulchakkaravarthi, N. P. Rajesh et al., “Synthesis, crystal growth and FTIR, NMR, SHG studies of 4-methoxy benzaldehyde-N-methyl-4-stilbazolium tosylate (MBST),” Journal of Crystal Growth, vol. 240, no. 1-2, pp. 212– 217, 2002. [6] W. Yu, L. Yang, T.-L. Zhang et al., “Crystal structure and geometry-optimization study of 4-methyl-3 ,5 -dinitro-4 methyl benzylidene aniline,” Journal of Molecular Structure, vol. 794, no. 1-3, pp. 255–260, 2006. [7] K. Srinivasan, R. Biravaganesh, R. Gandhimathi, and P. Ramasamy, “Growth and characterization of NMBA (4-nitro4 -methyl benzylidene aniline) single crystals,” Journal of Crystal Growth, vol. 236, no. 1-3, pp. 381–392, 2002. [8] R. J. Xu, “4-Methoxyanilinium iodide,” Acta Crystallographica E, vol. 66, article o1794, 2010. [9] Y. le Fur, R. Masse, M. Z. Cherkaoui, and J. F. Nicuod, “Crystal structure of ethyl-2,6-dimethyl-4(1H)-pyridinone, trihydrate: a potential nonlinear optical crystalline organic material transparent till the near ultraviolet range,” Zeitschrift f¨ur Kristallographie, vol. 210, pp. 856–860, 1995. [10] V. Krishnakumar, R. Nagalakshmi, and P. Janaki, “Growth and spectroscopic characterization of a new organic nonlinear optical crystal-8-hydroxyquinoline,” Spectrochimica Acta A, vol. 61, no. 6, pp. 1097–1103, 2005. [11] K. Jagannathan, S. Kalainathan, and T. Gnanasekaran, “Microhardness studies on 4-Dimethylamino-N-methyl 4Stilbazolium Tosylate (DAST),” Materials Letters, vol. 61, no. 23-24, pp. 4485–4488, 2007.
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