CRYSTAL GROWTH & DESIGN
Spectral, Dielectric, and Thermal Properties of Triketohydrindane Hydrate Single Crystals
2009 VOL. 9, NO. 5 2061–2064
T. Kishore Kumar,† S. Janarthanan,† S. Pandi,† S. Selvakumar,‡ and D. Prem Anand*,§ Department of Physics, Presidency College, Chennai-600005, India, Department of Physics, Loganatha Narayanasamy GoVernment College, Ponneri-601204, India, and Department of Physics, St. XaVier’s College, Palayamkottai-627002, India ReceiVed NoVember 9, 2007; ReVised Manuscript ReceiVed February 24, 2009
ABSTRACT: Single crystals of an organic nonlinear optical (NLO) material, triketohydrindane hydrate (THH), were synthesized. Bulk size crystals of THH were successfully grown by slow evaporation of the aqueous solution at room temperature for the first time. THH was subjected to single crystal X-ray diffraction, Fourier transform infrared spectroscopy, NMR, UV-vis-NIR, NLO, dielectric and thermal studies. The UV transparency cut off wavelength of THH crystal is around 260 nm. The thermogravimetric analysis curve of THH shows that the sample undergoes two steps of decomposition. The formation of the material was confirmed qualitatively by 1H and 13C NMR spectral analyses. The nature of variation of dielectric constant (εr) and dielectric loss (D) with frequency at different temperatures was investigated. Introduction Recent advances in nonlinear optical (NLO) materials have involved a large revival of interest in the area of optoelectronics on account of their widespread industrial requirements. Organic materials have been demonstrated in recent years to possess superior second- and third-order NLO properties compared to the more traditional inorganic materials. The structural flexibility of organic compounds is an asset for materials with optimized second-order nonlinear susceptibility, fast response, and tailormade flexibility.1 An innumerable number of organic crystals are synthesized and grown in this fashion.2-7 One of the obvious requirements for nonlinear crystal is that it should have excellent optical quality. For a device to succeed, it is vital that it should meet a number of criteria such as optical nonlinearity, chemical stability, and thermal stability for lifetime and system capability.8 The present communication deals with the synthesis of an organic material and growth of triketohydrindane hydrate (THH) single crystals. The grown crystals have been subjected to various characterization methods such as X-ray diffraction, Fourier transform infrared spectroscopy, 1H and 13C NMR, UV-vis-NIR, second harmonic generation (SHG) testing with an insight to learn the properties of the material. Dielectric and TG/DTA studies were done on the sample.
Figure 1. Solubility curve of THH crystal. a distilled flask, and it was distilled with 180 mL of dioxin. 100 mL of distilled water was added to the filtrate. The solution was boiled to coagulate the sample. Finally the filtrate was boiled with 0.2 g of decolorizing carbon, and the mixture was kept at room temperature as such and colorless salt of THH hydrate was obtained. Approximately 3.6 g of THH were obtained.
Results Experimental Procedures 9
Synthesis. According to the reports available in the literature, THH synthesis was carried out using a simple alternative route. The starting materials such as dioxin, selenium dioxide, and 1:3 indanedione are commercially available. The step-by-step synthesis procedure of THH is as follows. Eleven grams of resublimed selenium dioxide dissolved in 240 mL of dioxin and 5 mL of distilled water were taken together in a 500 mL round-bottom flask fitted with a reflux container and mechanical stirrer. The mixture was heated to 60-70 °C. In order to remove the source of heat generated in the flask, the flask was removed from the stirrer and kept as such for 1 h. Now 15 g of 1:3 indanedione was added to the mixture, and the resulting mixture was refluxed for 6 h, in order to obtain the filtrate. Again the filtrate was transferred to * To whom correspondence should be addressed. E-mail: dpremanand@ yahoo.co.in. Phone: +919994292586. † Presidency College. ‡ Loganatha Narayanasamy Government College. § St. Xavier’s College.
Solubility and Growth. The solubility study of THH was carried out by measuring the amount of THH salt that dissolved in water at 30, 35, 40, 45, and 50 °C. Figure 1 shows the solubility of THH in 50 mL of double distilled water at different temperatures. It is seen from the solubility curve that the solubility increases with temperature. The synthesized salt was taken and the saturated solution was prepared in accordance with the solubility data. Seed crystals were formed by spontaneous nucleation process. Defect-free, optically clear, and perfectly shaped tiny crystals were chosen as seeds for the growth experiment. Figure 2 shows the photograph of as-grown THH single crystal. Bulk size crystals of dimension 33 × 9 × 5 mm3 were conveniently grown in a period of 30-40 days. Single Crystal XRD. The crystallization of hybrid compound provides a convenient sized crystal to perform a single crystal X-ray diffraction study. Single crystal XRD data for THH were recorded using an X-ray diffractometer (MESSRS ENRAF
10.1021/cg701111e CCC: $40.75 2009 American Chemical Society Published on Web 03/25/2009
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Figure 2. Photograph of as-grown THH single crystal.
NONIUS, The Netherlands) with a Cu KR radiation λ ) 1.5406 Å. It is observed that THH single crystal belongs to monoclinic crystal system with the space group P21 and the unit cell dimensions are a ) 11.23 Å, b ) 5.97 Å, c ) 5.67 Å, and R ) γ ) 90°, β ) 98.32°. The volume of the unit cell is 380.13 Å3. The observed data are in very good agreement with the reported values.10 FT-IR Studies. FT-IR analysis of THH was carried out to investigate the presence of functional groups. The sample was prepared by mixing with KBr pellet. The FT-IR spectrum of THH is shown in Figure 3. The spectrum was recorded using the instrument Bruker model IFS 66V, FT-IR spectrometer in the range of 400-4000 cm-1. A peak at 3240 cm-1 is assigned to O-H stretching. The aromatic C-H stretching is assigned at 3050 cm-1. CdO stretching modes are observed at 1718 and 1746 cm-1, respectively. The aromatic ring stretching is observed at 1592 cm-1. O-H bending modes and C-O stretching are positioned at 1387 and 1186 cm-1, respectively. 1 H and 13C NMR Spectral Studies. To determine the molecular structure, the hydrogen and carbon network in THH
Figure 3. FT-IR spectrum of THH.
Figure 4. 1H spectrum of THH.
was studied using these analyses. 1H and 13C NMR spectra of THH sample were recorded using a JEOL: GSX 500 instrument in DMSO-d6 solvent with tetramethylsilane (TMS) as an internal standard. Figures 4 and 5 represent 1H and 13C NMR spectra, respectively. The two signals around 7.9 ppm are due to protons from the aromatic phenyl ring. The strong signal at 3.9 ppm is due to the protons from the two OH groups. In the 13C spectrum, the signal at 197.55 ppm represents the two carbonyl carbons (CdO). The signals ranging from 124 to 138 ppm are due to aromatic carbons from the phenyl ring. The signal at 89 ppm is due to the carbon which is attached to two OH groups. Thus, the molecular structure of THH is confirmed by 1H and 13C NMR spectral studies. UV-vis-NIR Analysis. The absorption spectrum of THH crystal was recorded in the wavelength range of 200-1200 nm covering the near-UV, entire visible, and near-infrared regions
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Figure 5. 13C spectrum of THH. Figure 8. Variation of dielectric loss of THH crystal as a function of log frequency.
Figure 6. UV-vis-NIR absorption spectrum of THH.
Figure 9. Variation of dielectric constant of THH crystal as a function of temperature.
Figure 7. Variation of dielectric constant of THH crystal as a function of log frequency.
using a VARIAN CARY 5E-model spectrophotometer. Figure 6 shows the UV-vis-NIR spectrum of as grown crystal of THH. The near-infrared region of 800-1200 nm absorbance was not noticed until a wavelength of 1100 nm is reached. The information provided by the absence of absorption spectra in the range of 460-860 nm reveals that the synthesized compound is transparent in this visible range. Additionally, there are two broad absorption bands at 900 and 1000 nm. These bands may be due to either overtones or combination bands of either stretching or bending vibrations in the middle infrared region. Dielectric Studies. To carry out the dielectric measurements, a selected sample of THH was carefully cut and was polished using paraffin oil and fine grade alumina powder so as to obtain a good surface finish. Dielectric permittivity measurements were carried out with the silver coated sample placed inside a
dielectric cell in the frequency range 50 Hz to 5 MHz using a HIOKI 3532-50 LCR HiTESTER impedance meter. The temperature was varied from 308 to 368 K. Figure 7 shows the plot of dielectric constant (εr) as a function of log frequency with different temperatures, and Figure 8 shows the plot of dielectric loss (D) as a function of log frequency with different temperatures. It is observed from the plots that both εr and D show similar variation with frequency. Broadly speaking, the graph exemplifies the fact that both the dielectric constant and the dielectric loss are inversely proportional to frequency. This is a normal dielectric behavior11 that both εr and D decrease with increasing frequency, and this can be on the basis that the mechanism of polarization is similar to that of the conduction process. The electronic exchange of the number of ions in the crystals gives local displacement of electrons in the direction of the applied field, which in turn gives rise to polarization. As the frequency increases, a point will be reached where the space charge cannot sustain and comply with the external field, and hence the polarization decreases giving rise to diminishing values of εr and D. A continuous gradual decrease in εr as well D suggests that THH crystal, like any normal dielectric, may have domains of different sizes and varying relaxation times. Dielectric constant was also plotted as a function of temperatures at different frequencies. The temperature was increased in steps of every 20 K starting from 308 to 368 K. The temperature
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Figure 10. TG/DTA curves of THH.
dependence of the real part (εr) of the dielectric constant is shown Figure 9. At a particular frequency, the dielectric constant was found to be almost constant for varying the temperatures. TG/DTA. To analyze the thermal stability and confirm the melting point of the material, thermogravimetric (TG) and differential thermal analysis (DTA) were carried out (Figure 10) in nitrogen atmosphere at a heating rate of 20 °C/min in the temperature range of 10-1200 °C using a NETZSCH STA 409 C thermal analyzer. It is found from the TG trace that there is a weight loss observed and the sample undergoes an irreversible endothermic transition at 180 °C. The DTA curve shows that THH melts at a temperature around 178 °C, and it undergoes endothermic transition around 290 °C. NLO Tests. The SHG tests on the THH were performed by the Kurtz and X-ray powder SHG method. The crystal was powdered by sandwiching the graded crystalline powder with an average particle size of about 90 µm between two quartz slides using a copper space of 0.4 mm thickness. The sample was illuminated using a Q-switched, mode locked Nd:YAG laser with modulated radiation corresponding to the first harmonic output of 1064 nm with a pulse width of 8 ns. The doubling of frequency was confirmed by the emission of green radiation of wavelength 532 nm collected by a monochromator after separating the 1064 nm pump beam with an IR-blocking filter. The second harmonic signal generated in the crystal was confirmed from the emission of green radiation by THH. The NLO property of THH also has been measured.12 Conclusions A bulk size crystal of THH was successfully grown by the slow evaporation technique at room temperature. The structure of the grown crystal was confirmed by single crystal XRD. The functional groups of THH crystalline sample were identified using FT-IR and 1H and 13C spectral analyses. Optical absorption spectrum confirms that the crystal exhibits nearly zero absorption in range 460-860 nm. The characteristic of low dielectric loss at high frequencies for the sample suggest that THH possesses enhanced optical quality with lesser defects. From thermal
studies, it was found that the sample is stable up to 180 °C. The SHG of the sample was confirmed by the Kurtz technique. SHG efficiency measurements and etching studies are in progress. Acknowledgment. It is a pleasure to acknowledge Dr. L. Joseph Milton Gaspar, Research Associate, Polymat, The University of the Basque Country, San Sebastian, Spain, Dr. John Maria Xavier, Department of Chemistry, Loyola College, Chennai, and Dr. M. Palanichamy, Department of Chemistry, Anna University, Chennai, for their constant help, support, and encouragement.
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