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Growth of ninhydrin single crystal and its characterization
Spectrochimica Acta Part A 71 (2009) 1667–1672
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Growth of ninhydrin single crystal and its characterization T. Uma Devi a,∗ , N. Lawrence b , R. Ramesh Babu c , K. Ramamurthi c , G. Bhagavannarayana d a
Department of Physics, Cauvery College for Women, Annamalainagar, Tiruchirappalli 620018, India Department of Physics, St.Joseph’s College (Autonomous), Tiruchirappalli 620002, India c Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, India d Materials Characterization Division, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India b
a r t i c l e
i n f o
Article history: Received 1 November 2007 Received in revised form 16 June 2008 Accepted 23 June 2008 PACS: 81.10Dn 81.70Pg 32.30Jc
a b s t r a c t A novel organic nonlinear optical crystal ninhydrin having good optical quality was grown by solution technique using aqua solution. The quality of the crystal was also examined by high-resolution X-ray diffraction study. Solubility studies were made at different temperatures. Functional groups present in the grown material were identified from the vibrational frequencies of recorded FTIR spectrum. Transmittance of the crystal was recorded using the UV–vis–NIR spectrophotometer. From the thermal analysis it was observed that the material exhibits single sharp melting point. The fluorescence spectrum of ninhydrin was recorded. The Vicker’s microhardness values were measured for the grown crystal. Second harmonic generation conversion efficiency estimated using Kurtz and Perry method is about five times that of KDP. © 2008 Elsevier B.V. All rights reserved.
Keywords: Solubility Growth from solutions Single crystal growth Nonlinear optical materials
1. Introduction In recent years, organic materials with aromatic rings having high nonlinear optical coefficient, higher laser damage threshold, fast response with tailor-made flexibility, low mobility and large band gap find wide applications [1–4]. Ninhydrin is one of such organic materials, with high melting point and it is a compound with two hydroxyl groups attached to the same carbon atom. Ninhydrin is also an important analytical tool in various fields including soil biology [5], chemistry [6], agriculture [7], medicine [8], forensic [9], food sciences [10,11], pharmacology [12] and so on. It is used as a potential material for micromolar determination of human serum albumin based on chemiluminescence [13] and in antimicrobial activity [14]. Ninhydrin crystallizes in a noncentrosymmetric structure (space group P21 ) [15]. To our knowledge no systematic studies on the growth and characterization of ninhydrin have been reported. Hence, in the present investigation we report on the growth and characterization of ninhydrin single crystals by XRD, Fourier transform infrared (FTIR), thermal and UV–vis–NIR studies. The quality of the grown crystal was also examined by high-resolution X-ray diffraction study. SHG
∗ Corresponding author. Tel.: +91 431 2751232; fax: +91 431 2407045. E-mail address: kavin [email protected] (T. Uma Devi). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.06.034
efficiency of the powdered crystal was tested using Kurtz and Perry method. 2. Experimental details 2.1. Solubility Ninhydrin (C9 H6 O4 ) is an aromatic compound and its chemical structure is shown in Fig. 1. The recrystallized salt was added in small quantity to a beaker containing 100 ml of double distilled water at 30 ◦ C by stirring the solution continuously. Saturation level of ninhydrin at 30 ◦ C was estimated by gravimetric method. This experimental procedure was repeated and the solubility of ninhydrin was estimated for 35, 40, 45, 50 and 55 ◦ C. 2.2. Metastable zonewidth Metastable zonewidth, an experimentally measurable quantity, depends on number of factors, such as stirring rate, cooling rate of the solution, the physio-chemical property of the material and presence of additional impurities [16–18]. Ninhydrin solution was prepared in accordance with the presently determined solubility data and nucleation experiments were carried out by adopting polythermal method [19]. The required amount of recrystallized ninhydrin salt was added to 100 ml of double distilled water taken
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Fig. 1. Chemical structure of ninhydrin.
in a container. The solution was stirred continuously using a magnetic stirrer and saturated at 30 ◦ C. The temperature of the solution was raised by 5 ◦ C above the saturated temperature to attain homogeneous solution. The solution was cooled from this preheated temperature to a temperature at which the first speck of the particle appeared. This corresponds to the width of metastable zone at that particular temperature. The same experimental procedure was repeated to estimate metastable zonewidth at different temperatures viz., 35, 40, 45, 50 and 55 ◦ C. The solubility and metastable zonewidth of ninhydrin estimated as a function of temperature is shown in Fig. 2. 2.3. Crystal growth Temperature reduction technique was employed to grow single crystal of ninhydrin. Recrystallized salt of ninhydrin was used to prepare saturated solution at 35 ◦ C and the solution was kept in a constant temperature bath having an accuracy of ±0.01 ◦ C. One of the good quality single crystals got from slow evaporation at room temperature was used as the seed crystal. The growth process was initiated at a temperature of 35 ◦ C and the temperature was reduced at a rate of 0.2 ◦ C per day. After a growth period of 10 days, well-developed single crystal of ninhydrin of dimension 11 mm × 10 mm × 7 mm was harvested (Fig. 3a). The crystal morphology of the ninhydrin crystal is shown in Fig. 3b. 3. Characterization 3.1. X-ray diffraction analyses 3.1.1. Single crystal and powder X-ray diffraction Single crystal X-ray diffraction study, was carried out on the as grown ninhydrin single crystal. The present study shows that ninhydrin crystallizes in a monoclinic system. The unit cell parameters
Fig. 2. Metastable zonewidth of ninhydrin.
Fig. 3. (a) As grown ninhydrin crystal and (b) morphology of ninhydrin crystal.
calculated are a = 11.3387 Å, b = 6.0081 Å, c = 5.7526 Å, ˛ = = 90◦ , ˇ = 98.72◦ and V = 387.354 Å3 . These values agree well with reported values [15], confirming that the crystal belongs to the P21 space group. Also, the powder XRD pattern of ninhydrin was recorded and indexed is depicted in Fig. 4. 3.1.2. Multicrystal X-ray diffractometry A multicrystal X-ray diffractometer designed and developed at National Physical Laboratory [20,21] has been used to study the crystalline perfection of this crystal. The divergence of the X-ray beam emerging from a fine focus X-ray tube (Philips X-ray Generator; 0.4 mm × 8 mm; 2 kW Mo) is first reduced by a long collimator fitted with a pair of fine slit assemblies. This collimated beam is diffracted twice by two Bonse-Hart [21] type of monochromator
Fig. 4. X-ray powder diffractogram of ninhydrin.
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crystals and the thus diffracted beam contains well-resolved Mo K␣1 and Mo K␣2 components. The Mo K␣1 beam is isolated with the help of fine slit arrangement and allowed to further diffract from a third (1 1 1) Si monochromator crystal set in dispersive geometry (+,−,−). Due to dispersive configuration, though the lattice constant of the monochromator crystal and the specimen are different, the dispersion broadening in the diffraction curve of the specimen does not arise. Such an arrangement disperses the divergent part of the Mo K␣1 beam away from the Bragg diffraction peak and thereby gives a good collimated and monochromatic Mo K␣1 beam at the Bragg diffraction angle, which is used as incident or exploring beam for the specimen crystal. The dispersion phenomenon is well described by comparing the diffraction curves recorded in dispersive (+,−,−) and non-dispersive (+,−,+) configurations. This arrangement improves the spectral purity (/ 10−5 ) of the Mo K␣1 beam. The divergence of the exploring beam in the horizontal plane (plane of diffraction) was estimated to be 3 arcsec. The specimen occupies the fourth crystal stage in symmetrical Bragg geometry for diffraction in (+,−,−,+) configuration. The specimen can be rotated about a vertical axis, which is perpendicular to the plane of diffraction, with minimum angular interval of 0.5 arcsec. The diffracted intensity is measured by using an in-house (NPL) developed scintillation counter. To provide two-theta (2 B ) angular rotation to the detector (scintillation counter) corresponding to the Bragg diffraction angle ( B ), it is coupled to the radial arm of the goniometer of the specimen stage. The rocking or diffraction curves were recorded by changing the glancing angle (angle between the incident X-ray beam and the surface of the specimen) around the Bragg diffraction peak position B starting from a suitable arbitrary glancing angle. The detector was kept at the same angular position 2 B with wide opening for its slit, the so-called scan. Before recording the diffraction curve, to remove the noncrystallized solute atoms remained on the surface of the crystal and also to ensure the surface planarity, the specimen was first lapped and chemically etched in a nonpreferential etchent of water and acetone mixture in 1:2 volume ratio. Fig. 5 shows the highresolution rocking or diffraction curve (DC) recorded for a typical ninhydrin crystal using (0 0 1) diffracting planes in symmetrical Bragg geometry by employing the multicrystal X-ray diffractometer described above with Mo K␣1 radiation. As seen in the figure the DC is quite sharp without any satellite peaks, which may otherwise be observed due to internal structural grain boundaries [22]. The full width at half maximum (FWHM) of the diffraction curves is 22 arcsec, which is close to that expected from the plane wave dynamical theory of X-ray diffraction [23]. It is interesting to see the asymmetry of the DC with respect to the peak position. For a particular angular deviation () of glancing angle with respect
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Fig. 6. FTIR spectrum of ninhydrin.
to the peak position, the scattered intensity is more in the positive direction in comparison to that of the negative direction. This feature indicates that the crystal contains some interstitial type of point defects [20], which may be due to self-interstitials (atoms or molecules of the parent material occupied the interstitial space of the crystal lattice) or solvent molecules or impurities occupied interstitially in the crystalline matrix. However, the single sharp diffraction curve with low FWHM indicates that the crystalline perfection is very good. The density of point defects is however very meager and in all most all real including nature gifted crystals, these are unavoidable. More details may be obtained from the study of high-resolution diffuse X-ray scattering measurements [20], which is not the main focus of the present investigation. The specimen is a nearly perfect single crystal without having any internal structural grain boundaries and may be with a very low density of dislocations. It may be mentioned here that because of the high-resolution of the multicrystal X-ray diffractometer used in the present investigation, such minute details in the shape of the DC could be observed which indicate the nature of point defects. 3.2. Fourier transform infrared spectroscopic studies Fourier transform infrared spectrum was recorded in the range of 400–4000 cm−1 using KBr pellet technique (Fig. 6) and the following group frequencies were identified. Aromatic C–H stretching is observed at 3089 cm−1 . Peaks at 3501 and 3238 cm−1 are due to OH vibrations. The recorded peak at 1748 cm−1 is due to carbonyl (C O) stretching. Skeletal vibrations of aromatic rings are observed at 1589 cm−1 [24]. The peaks at 1063, 1152, 1185, 1256, 1256 and 1291 cm−1 are all due to in plane bending modes of aromatic C–H bonds. The out of plane aromatic C–H bond is observed at 740 cm−1 [25]. 3.3. Optical transmittance spectrum
Fig. 5. Diffraction curve recorded for a typical SEST-grown ninhydrin single crystal recorded for (0 0 1) diffracting planes by employing the multicrystal X-ray diffractometer with Mo K␣1 radiation.
Optical transmission spectrum is very important for any NLO material because a nonlinear optical material can be of practical use if it has wide transparency window. The optical transmittance spectrum of ninhydrin was recorded using Shimadzu spectrophotometer model 1601. The spectrum recorded in the range of 300–1000 nm is shown in Fig. 7a. Optically clear single crystal of thickness about 1 mm was used for this study. The optical transmittance study shows that ninhydrin has less absorption around 532 nm, which has a significant contribution towards the resistance to laser induced damage. This crystal can be utilized for SHG from
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tion rate of 10 Hz was used. The grown single crystal of ninhydrin was powdered with a uniform particle size and then packed in a microcapillary tube of uniform bore and exposed to laser radiation. The output from the sample was monochromated to collect the intensity of 532 nm component and to eliminate the fundamental frequency. Second harmonic radiation generated by the randomly oriented microcrystals was focused by a lens and detected by a photo multiplier tube. The generation of the second harmonics was confirmed by the emission of green light. A sample of potassium dihydrogen phosphate (KDP), also powdered to the same particle size as the experimental sample, was used as reference material for the present measurement. It is found that the SHG efficiency of the ninhydrin is better than KDP (Table 1). This may be attributed to
Fig. 7. (a) UV–vis–NIR spectrum of ninhydrin; (b) graph of h vs. (˛h)2 .
a laser operating at 1064 nm or other optical applications in blue region [26]. The value of band gap energy was estimated from the graph between h and (˛h)2 by extrapolating the linear portion of the curve to zero absorption as shown in Fig. 7b. Here ˛ is the absorption coefficient and h is the photon energy. The band gap energy estimated is about 2.5 eV for the ninhydrin single crystal. 3.4. Powder SHG test The study of nonlinear optical conversion efficiency was carried out using the modified experimental setup of Kurtz and Perry [27]. A Q-switched Nd:YAG laser beam of wavelength 1064 nm, with an input power of 2.8 mJ, and pulse of width 8 ns with a repetiTable 1 SHG signal energy output Input power (mJ/pulse)
KDP (mV)
Urea (V)
Ninhydrin (V)
2.8
510
2.75
2.55
Table 2 Comparison of NLO property of various NLO crystals (with respect to KDP) S.NO
NLO crystals
Reference
SHG efficiency
1 2 3 4 5 6
l-prolinium tartrate NaAP l-arginine trifluoroacetate -Glycine Indole-3-aldehyde Ninhydrin
[29] [30] [31] [32] [33] Present work
0.9 1.10 2.50 3.00 1.67 5.00
Fig. 8. (a) Plot of hardness vs. load; (b) log P vs. log d for ninhydrin crystal; (c) PSR plot of P/d vs. d for ninhydrin crystal.
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Fig. 9. DTA and TGA of ninhydrin crystal.
the favourable nature of the two types of hydrogen bonds; namely hydroxyl–hydroxyl bonds and hydroxyl–carbonyl bonds. Hydrogen bonds give rise to the possible generation of noncentrosymmetric structures, which is a prerequisite for an effective SHG crystal [28]. A comparison of NLO property of ninhydrin crystal with a few wellknown NLO crystals is presented in Table 2. Since ninhydrin has the ability to coordinate with metal ions, further work on the doping the ninhydrin with rare earth metal ions are in progress. 3.5. Mechanical properties Hardness is one of the important mechanical properties to determine the plastic nature and strength of a material. Microhardness measurements were carried out using Leitz Weitzler hardness tester fitted with a diamond indentor. The well-polished ninhydrin 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 indentation time was kept as 8 s for all the loads. The hardness number was calculated using the relation Hv = (1.8544P)/(d2 ) kg/mm2 , where P is the applied load in kg and
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d is the diagonal length of the indentation impression in micrometer. The relation between hardness number (Hv ) and load (P) for ninhydrin is shown in Fig. 8a. The hardness increases gradually with the increase of load and above 200 g cracks develop on the (0 0 1) plane of the crystal due to the release of internal stresses generated locally by indentation. The work hardening coefficient n was calculated from Meyer’s law [34]. The n values calculated by plotting log P against log d (Fig. 8b) for ninhydrin crystal on (0 0 1) plane is 3. Onitsch [35] inferred that a value of n lies between 1 and 1.6 for hard materials and for soft materials it is above 1.6. Thus the ninhydrin comes under the soft materials category. Since the value of n is greater than 2, the hardness of the material is found to increase with the increase of load confirming the prediction of Onitsch [35]. A plot of P/d against d (Fig. 8c) drawn following proportional specimen resistance (PSR) model will be a straight line, the slope of which gives the load independent microhardness [36]. The load independent microhardness value is calculated from the slope (P/d2 ), which, when multiplied by Vicker’s conversion factor 1.8544 gives 37 kg/mm2 for ninhydrin. 3.6. Thermal analysis Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) of ninhydrin were carried out simultaneously employing NETZCH STA 409 Thermal Analyzer are shown in Fig. 9. 1.88 mg of ninhydrin was taken and heated at a rate of 20 ◦ C/min in inert nitrogen atmosphere. There is a sharp weight loss with the maximum at about 146 ◦ C. It is due to loss of water of crystallization. This weight loss is followed by a major weight loss pattern between 155 and 254 ◦ C due to melting of the compound. There is a sharp endotherm with a maximum at 146 ◦ C. It coincides with the first stage of weight loss in the TGA trace. There is one sharper endotherm at 248.98 ◦ C. This endotherm is assigned to melting of the compound, which is close to the value reported earlier [15]. The sharpness of the thermogram is also illustrative of the crystal purity without association of any impurities [37,38]. 3.7. Fluorescence studies Fluorescence finds wide application in the branches of biochemical, medical, and chemical research fields, for analyzing organic
Fig. 10. (a) Excitation spectrum and (b) emission spectrum.
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compounds. Fluorescence may be expected generally in molecules that are aromatic or contain multiple conjugated double bonds with a high degree of resonance stability [39]. Hence the excitation and emission spectra for ninhydrin were recorded using FP-6500 Spectrofluorometer. The excitation spectrum was recorded in the range 220–350 nm and the sample was excited at 290 nm (Fig. 10a). The emission spectrum was measured in the range 350–540 nm. Peaks at 450 and 470 nm were observed in the emission spectrum (Fig. 10b). The results indicate that ninhydrin crystal has a blue fluorescence emission. 4. Conclusion Optically good quality single crystal of ninhydrin was grown using temperature reduction technique. Single crystal X-ray diffraction study shows that ninhydrin crystallizes in a monoclinic system. A multicrystal X-ray diffractometer study reveals the crystalline perfection of the crystal without any internal structural grain boundaries. FTIR spectrum recorded in the range of 400–4000 cm−1 indicates the vibrational frequencies of the functional group such as aromatic C–H stretching, OH vibrations and carbonyl (C O) stretching. Optical transmission studies confirm that ninhydrin is transparent in the entire visible region and the band gap energy is 2.5 eV. Microhardness measurements imply that the ninhydrin comes under the soft materials category. TGA reveals that the sample is thermally stable and has higher melting point. The Kurtz powder studies on the NLO property showed that the second harmonic conversion efficiency is about five times that of KDP. References [1] C.K. Lakshmana Perumal, A. Arulchakkaravarthi, N.P. Rajesh, P. Santhana Raghavan, Y.C. Huang, M. Ichimura, P. Ramasamy, J. Cryst. Growth 240 (2002) 212–217. [2] C.W. Tang, S.A. Van Slyke, Appl. Phys. Lett. 51 (1987) 913–915. [3] L.R. Dalton, Pure Appl. Chem. 76 (2004) 1421–1433. [4] K. Jagannathan, S. Kalainathan, T. Gnanasekaran, N. Vijayan, G. Bhagavannarayana, Cryst. Res. Technol. 42 (2007) 483–487. [5] C. Mondini, A. Monedero, L. Leita, G. Bragato, M. De Nobili, Commun. Soil Sci. Plant Anal. 28 (1997) 113–122. [6] D.B. Hansen, M.M. Joullié, Chem. Soc. Rev. 34 (2005) 408–417.
[7] M. Friedman, J. Agric. Food Chem. 52 (2004) 385–406. [8] K.R. Prabhakar, V.P. Veerapur, Punit Bansal, K. Parihar Vipan, K.M. Reddy, Atanu Barik, B.K.D. Reddy, P. Reddanna, K.I. Priyadarsini, M.K. Unnikrishnan, Bioorg. Med. Chem. 14 (2006) 7113–7120. [9] R. Elber, A. Frank, J. Almog, J. Forensic Sci. 45 (2000) 757–760. [10] R.V. Barbehennr, J. Sci. Food Agric. 69 (1995) 353–359. [11] P.M.S. Giovannetti, C. Stothers, Growth 39 (1975) 1–16. [12] S. Lenzen, F.H. Brand, U. Panten, Br. J. Pharmacol. 95 (1988) 851–859. ˜ M.E. Díaz-García, J. Lumin. 118 (2006) 193–198. [13] M.R. Alvarez, R.B. Laíno, [14] N.S.R.R.M.M. Koteswara Rao, M.G. Ram Reddy, Biometals 3 (1990) 19–23. [15] R.C. Medrud, Acta Cryst. B 25 (1969) 213–220. [16] J. Nyvlt, R. Rychly, J. Gottfried, J. Wurzelova, J. Cryst. Growth 6 (1970) 151–162. [17] K. Udhaya Lakshmi, K. Ramamurthi, Cryst. Res. Technol. 40 (2005) 1165–1168. [18] P.M. Ushashree, R. Muralidharan, R. Jayavel, P. Ramasamy, J. Cryst. Growth 218 (2000) 365–371. [19] N.P. Zaitseva, L.N. Rashkovich, S.V. Bagatyarek, J. Cryst. Growth 148 (1995) 276–282. [20] G. Bhagavannarayana, A. Choubey, V.Y. Shubin, K. Lal, J. Appl. Cryst. 38 (2005) 448–454. [21] U. Bonse, M. Hart, Appl. Phys. Lett. 7 (1965) 238–240. [22] G. Bhagavannarayana, R.V. Ananthamurthy, G.C. Budakoti, B. Kumar, K.S. Bartwal, J. Appl. Cryst. 38 (2005) 768–771. [23] B.W. Betterman, H. Cole, Rev. Mod. Phys. 36 (1964) 681–717. [24] R.J. Dyer, Applications of Absorption Spectroscopy of Organic Compounds, Prentice-Hall of India, New Delhi, 1994. [25] K. Biemann, Tables of Spectral Data for Structure Determination of Organic Compounds, Springer Verlag, Heidelberg, Berlin, 1989. [26] V. Krishnakumar, R. Nagalakshmi, P. Janaki, Spectrochim. Acta A 61 (2005) 1097–1103. [27] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798–3813. [28] J.A.R.P. Sarma, J. Laxmikanth Rao, K. Bhanuprakash, Chem. Mater. 7 (1996) 1843–1848. [29] S.A. Martin Britto Dhas, S. Natarajan, Cryst. Res. Technol. 42 (2007) 471–476. [30] R. Bairava Ganesh, V. Kannan, K. Meera, N.P. Rajesh, P. Ramasamy, J. Cryst. Growth 282 (2005) 429–433. [31] Z.H. Sun, D. Xu, X.Q. Wang, X.J. Liu, G. Yu, G.H. Zhang, L.Y. Zhu, H.L. Fan, Cryst. Res. Technol. 42 (2007) 812–816. [32] K. Ambujam, S. Selvakumar, D. Prem Anand, G. Mohamed, P. Sagayaraj, Cryst. Res. Technol. 41 (2006) 671–677. [33] A.S. Haja Hameed, G. Ravi, A. Nixon Azariah, T. Mahalingam, P. Ramasamy, J. Phys. Chem. Solids 64 (2003) 147–153. [34] H. Li, R.C. Bradt, J. Hard Mater. 3 (1992) 403–419. [35] E.M. Onitsch, Mikroskopie 2 (1947) 131–151. [36] H. Li, R.C. Bradt, Mater. Sci. Eng. A 142 (1991) 51–56. [37] N. Vijayan, R. Ramesh Babu, M. Gunasekaraan, R. Gopalakrishnan, R. Kumaresan, P. Ramasamy, C.W. Lan, J. Cryst. Growth 249 (2003) 309–315. [38] K.V. Rajendran, D. Jayaraman, R. Jayavel, P. Ramasamy, J. Cryst. Growth 254 (2003) 461–468. [39] H.H. Willard, L.L. Merritt Jr., J.A. Dean, F.A. Settle Jr., Instrumental Methods of Analysis, Sixth edition, Wadsworth Publishing Company, USA, 1986, p. 609.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Growth of ninhydrin single crystal and its characterization T. Uma Devi a,∗ , N. Lawrence b , R. Ramesh Babu c , K. Ramamurthi c , G. Bhagavannarayana d a
Department of Physics, Cauvery College for Women, Annamalainagar, Tiruchirappalli 620018, India Department of Physics, St.Joseph’s College (Autonomous), Tiruchirappalli 620002, India c Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, India d Materials Characterization Division, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India b
a r t i c l e
i n f o
Article history: Received 1 November 2007 Received in revised form 16 June 2008 Accepted 23 June 2008 PACS: 81.10Dn 81.70Pg 32.30Jc
a b s t r a c t A novel organic nonlinear optical crystal ninhydrin having good optical quality was grown by solution technique using aqua solution. The quality of the crystal was also examined by high-resolution X-ray diffraction study. Solubility studies were made at different temperatures. Functional groups present in the grown material were identified from the vibrational frequencies of recorded FTIR spectrum. Transmittance of the crystal was recorded using the UV–vis–NIR spectrophotometer. From the thermal analysis it was observed that the material exhibits single sharp melting point. The fluorescence spectrum of ninhydrin was recorded. The Vicker’s microhardness values were measured for the grown crystal. Second harmonic generation conversion efficiency estimated using Kurtz and Perry method is about five times that of KDP. © 2008 Elsevier B.V. All rights reserved.
Keywords: Solubility Growth from solutions Single crystal growth Nonlinear optical materials
1. Introduction In recent years, organic materials with aromatic rings having high nonlinear optical coefficient, higher laser damage threshold, fast response with tailor-made flexibility, low mobility and large band gap find wide applications [1–4]. Ninhydrin is one of such organic materials, with high melting point and it is a compound with two hydroxyl groups attached to the same carbon atom. Ninhydrin is also an important analytical tool in various fields including soil biology [5], chemistry [6], agriculture [7], medicine [8], forensic [9], food sciences [10,11], pharmacology [12] and so on. It is used as a potential material for micromolar determination of human serum albumin based on chemiluminescence [13] and in antimicrobial activity [14]. Ninhydrin crystallizes in a noncentrosymmetric structure (space group P21 ) [15]. To our knowledge no systematic studies on the growth and characterization of ninhydrin have been reported. Hence, in the present investigation we report on the growth and characterization of ninhydrin single crystals by XRD, Fourier transform infrared (FTIR), thermal and UV–vis–NIR studies. The quality of the grown crystal was also examined by high-resolution X-ray diffraction study. SHG
∗ Corresponding author. Tel.: +91 431 2751232; fax: +91 431 2407045. E-mail address: kavin [email protected] (T. Uma Devi). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.06.034
efficiency of the powdered crystal was tested using Kurtz and Perry method. 2. Experimental details 2.1. Solubility Ninhydrin (C9 H6 O4 ) is an aromatic compound and its chemical structure is shown in Fig. 1. The recrystallized salt was added in small quantity to a beaker containing 100 ml of double distilled water at 30 ◦ C by stirring the solution continuously. Saturation level of ninhydrin at 30 ◦ C was estimated by gravimetric method. This experimental procedure was repeated and the solubility of ninhydrin was estimated for 35, 40, 45, 50 and 55 ◦ C. 2.2. Metastable zonewidth Metastable zonewidth, an experimentally measurable quantity, depends on number of factors, such as stirring rate, cooling rate of the solution, the physio-chemical property of the material and presence of additional impurities [16–18]. Ninhydrin solution was prepared in accordance with the presently determined solubility data and nucleation experiments were carried out by adopting polythermal method [19]. The required amount of recrystallized ninhydrin salt was added to 100 ml of double distilled water taken
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Fig. 1. Chemical structure of ninhydrin.
in a container. The solution was stirred continuously using a magnetic stirrer and saturated at 30 ◦ C. The temperature of the solution was raised by 5 ◦ C above the saturated temperature to attain homogeneous solution. The solution was cooled from this preheated temperature to a temperature at which the first speck of the particle appeared. This corresponds to the width of metastable zone at that particular temperature. The same experimental procedure was repeated to estimate metastable zonewidth at different temperatures viz., 35, 40, 45, 50 and 55 ◦ C. The solubility and metastable zonewidth of ninhydrin estimated as a function of temperature is shown in Fig. 2. 2.3. Crystal growth Temperature reduction technique was employed to grow single crystal of ninhydrin. Recrystallized salt of ninhydrin was used to prepare saturated solution at 35 ◦ C and the solution was kept in a constant temperature bath having an accuracy of ±0.01 ◦ C. One of the good quality single crystals got from slow evaporation at room temperature was used as the seed crystal. The growth process was initiated at a temperature of 35 ◦ C and the temperature was reduced at a rate of 0.2 ◦ C per day. After a growth period of 10 days, well-developed single crystal of ninhydrin of dimension 11 mm × 10 mm × 7 mm was harvested (Fig. 3a). The crystal morphology of the ninhydrin crystal is shown in Fig. 3b. 3. Characterization 3.1. X-ray diffraction analyses 3.1.1. Single crystal and powder X-ray diffraction Single crystal X-ray diffraction study, was carried out on the as grown ninhydrin single crystal. The present study shows that ninhydrin crystallizes in a monoclinic system. The unit cell parameters
Fig. 2. Metastable zonewidth of ninhydrin.
Fig. 3. (a) As grown ninhydrin crystal and (b) morphology of ninhydrin crystal.
calculated are a = 11.3387 Å, b = 6.0081 Å, c = 5.7526 Å, ˛ = = 90◦ , ˇ = 98.72◦ and V = 387.354 Å3 . These values agree well with reported values [15], confirming that the crystal belongs to the P21 space group. Also, the powder XRD pattern of ninhydrin was recorded and indexed is depicted in Fig. 4. 3.1.2. Multicrystal X-ray diffractometry A multicrystal X-ray diffractometer designed and developed at National Physical Laboratory [20,21] has been used to study the crystalline perfection of this crystal. The divergence of the X-ray beam emerging from a fine focus X-ray tube (Philips X-ray Generator; 0.4 mm × 8 mm; 2 kW Mo) is first reduced by a long collimator fitted with a pair of fine slit assemblies. This collimated beam is diffracted twice by two Bonse-Hart [21] type of monochromator
Fig. 4. X-ray powder diffractogram of ninhydrin.
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crystals and the thus diffracted beam contains well-resolved Mo K␣1 and Mo K␣2 components. The Mo K␣1 beam is isolated with the help of fine slit arrangement and allowed to further diffract from a third (1 1 1) Si monochromator crystal set in dispersive geometry (+,−,−). Due to dispersive configuration, though the lattice constant of the monochromator crystal and the specimen are different, the dispersion broadening in the diffraction curve of the specimen does not arise. Such an arrangement disperses the divergent part of the Mo K␣1 beam away from the Bragg diffraction peak and thereby gives a good collimated and monochromatic Mo K␣1 beam at the Bragg diffraction angle, which is used as incident or exploring beam for the specimen crystal. The dispersion phenomenon is well described by comparing the diffraction curves recorded in dispersive (+,−,−) and non-dispersive (+,−,+) configurations. This arrangement improves the spectral purity (/ 10−5 ) of the Mo K␣1 beam. The divergence of the exploring beam in the horizontal plane (plane of diffraction) was estimated to be 3 arcsec. The specimen occupies the fourth crystal stage in symmetrical Bragg geometry for diffraction in (+,−,−,+) configuration. The specimen can be rotated about a vertical axis, which is perpendicular to the plane of diffraction, with minimum angular interval of 0.5 arcsec. The diffracted intensity is measured by using an in-house (NPL) developed scintillation counter. To provide two-theta (2 B ) angular rotation to the detector (scintillation counter) corresponding to the Bragg diffraction angle ( B ), it is coupled to the radial arm of the goniometer of the specimen stage. The rocking or diffraction curves were recorded by changing the glancing angle (angle between the incident X-ray beam and the surface of the specimen) around the Bragg diffraction peak position B starting from a suitable arbitrary glancing angle. The detector was kept at the same angular position 2 B with wide opening for its slit, the so-called scan. Before recording the diffraction curve, to remove the noncrystallized solute atoms remained on the surface of the crystal and also to ensure the surface planarity, the specimen was first lapped and chemically etched in a nonpreferential etchent of water and acetone mixture in 1:2 volume ratio. Fig. 5 shows the highresolution rocking or diffraction curve (DC) recorded for a typical ninhydrin crystal using (0 0 1) diffracting planes in symmetrical Bragg geometry by employing the multicrystal X-ray diffractometer described above with Mo K␣1 radiation. As seen in the figure the DC is quite sharp without any satellite peaks, which may otherwise be observed due to internal structural grain boundaries [22]. The full width at half maximum (FWHM) of the diffraction curves is 22 arcsec, which is close to that expected from the plane wave dynamical theory of X-ray diffraction [23]. It is interesting to see the asymmetry of the DC with respect to the peak position. For a particular angular deviation () of glancing angle with respect
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Fig. 6. FTIR spectrum of ninhydrin.
to the peak position, the scattered intensity is more in the positive direction in comparison to that of the negative direction. This feature indicates that the crystal contains some interstitial type of point defects [20], which may be due to self-interstitials (atoms or molecules of the parent material occupied the interstitial space of the crystal lattice) or solvent molecules or impurities occupied interstitially in the crystalline matrix. However, the single sharp diffraction curve with low FWHM indicates that the crystalline perfection is very good. The density of point defects is however very meager and in all most all real including nature gifted crystals, these are unavoidable. More details may be obtained from the study of high-resolution diffuse X-ray scattering measurements [20], which is not the main focus of the present investigation. The specimen is a nearly perfect single crystal without having any internal structural grain boundaries and may be with a very low density of dislocations. It may be mentioned here that because of the high-resolution of the multicrystal X-ray diffractometer used in the present investigation, such minute details in the shape of the DC could be observed which indicate the nature of point defects. 3.2. Fourier transform infrared spectroscopic studies Fourier transform infrared spectrum was recorded in the range of 400–4000 cm−1 using KBr pellet technique (Fig. 6) and the following group frequencies were identified. Aromatic C–H stretching is observed at 3089 cm−1 . Peaks at 3501 and 3238 cm−1 are due to OH vibrations. The recorded peak at 1748 cm−1 is due to carbonyl (C O) stretching. Skeletal vibrations of aromatic rings are observed at 1589 cm−1 [24]. The peaks at 1063, 1152, 1185, 1256, 1256 and 1291 cm−1 are all due to in plane bending modes of aromatic C–H bonds. The out of plane aromatic C–H bond is observed at 740 cm−1 [25]. 3.3. Optical transmittance spectrum
Fig. 5. Diffraction curve recorded for a typical SEST-grown ninhydrin single crystal recorded for (0 0 1) diffracting planes by employing the multicrystal X-ray diffractometer with Mo K␣1 radiation.
Optical transmission spectrum is very important for any NLO material because a nonlinear optical material can be of practical use if it has wide transparency window. The optical transmittance spectrum of ninhydrin was recorded using Shimadzu spectrophotometer model 1601. The spectrum recorded in the range of 300–1000 nm is shown in Fig. 7a. Optically clear single crystal of thickness about 1 mm was used for this study. The optical transmittance study shows that ninhydrin has less absorption around 532 nm, which has a significant contribution towards the resistance to laser induced damage. This crystal can be utilized for SHG from
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tion rate of 10 Hz was used. The grown single crystal of ninhydrin was powdered with a uniform particle size and then packed in a microcapillary tube of uniform bore and exposed to laser radiation. The output from the sample was monochromated to collect the intensity of 532 nm component and to eliminate the fundamental frequency. Second harmonic radiation generated by the randomly oriented microcrystals was focused by a lens and detected by a photo multiplier tube. The generation of the second harmonics was confirmed by the emission of green light. A sample of potassium dihydrogen phosphate (KDP), also powdered to the same particle size as the experimental sample, was used as reference material for the present measurement. It is found that the SHG efficiency of the ninhydrin is better than KDP (Table 1). This may be attributed to
Fig. 7. (a) UV–vis–NIR spectrum of ninhydrin; (b) graph of h vs. (˛h)2 .
a laser operating at 1064 nm or other optical applications in blue region [26]. The value of band gap energy was estimated from the graph between h and (˛h)2 by extrapolating the linear portion of the curve to zero absorption as shown in Fig. 7b. Here ˛ is the absorption coefficient and h is the photon energy. The band gap energy estimated is about 2.5 eV for the ninhydrin single crystal. 3.4. Powder SHG test The study of nonlinear optical conversion efficiency was carried out using the modified experimental setup of Kurtz and Perry [27]. A Q-switched Nd:YAG laser beam of wavelength 1064 nm, with an input power of 2.8 mJ, and pulse of width 8 ns with a repetiTable 1 SHG signal energy output Input power (mJ/pulse)
KDP (mV)
Urea (V)
Ninhydrin (V)
2.8
510
2.75
2.55
Table 2 Comparison of NLO property of various NLO crystals (with respect to KDP) S.NO
NLO crystals
Reference
SHG efficiency
1 2 3 4 5 6
l-prolinium tartrate NaAP l-arginine trifluoroacetate -Glycine Indole-3-aldehyde Ninhydrin
[29] [30] [31] [32] [33] Present work
0.9 1.10 2.50 3.00 1.67 5.00
Fig. 8. (a) Plot of hardness vs. load; (b) log P vs. log d for ninhydrin crystal; (c) PSR plot of P/d vs. d for ninhydrin crystal.
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Fig. 9. DTA and TGA of ninhydrin crystal.
the favourable nature of the two types of hydrogen bonds; namely hydroxyl–hydroxyl bonds and hydroxyl–carbonyl bonds. Hydrogen bonds give rise to the possible generation of noncentrosymmetric structures, which is a prerequisite for an effective SHG crystal [28]. A comparison of NLO property of ninhydrin crystal with a few wellknown NLO crystals is presented in Table 2. Since ninhydrin has the ability to coordinate with metal ions, further work on the doping the ninhydrin with rare earth metal ions are in progress. 3.5. Mechanical properties Hardness is one of the important mechanical properties to determine the plastic nature and strength of a material. Microhardness measurements were carried out using Leitz Weitzler hardness tester fitted with a diamond indentor. The well-polished ninhydrin 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 indentation time was kept as 8 s for all the loads. The hardness number was calculated using the relation Hv = (1.8544P)/(d2 ) kg/mm2 , where P is the applied load in kg and
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d is the diagonal length of the indentation impression in micrometer. The relation between hardness number (Hv ) and load (P) for ninhydrin is shown in Fig. 8a. The hardness increases gradually with the increase of load and above 200 g cracks develop on the (0 0 1) plane of the crystal due to the release of internal stresses generated locally by indentation. The work hardening coefficient n was calculated from Meyer’s law [34]. The n values calculated by plotting log P against log d (Fig. 8b) for ninhydrin crystal on (0 0 1) plane is 3. Onitsch [35] inferred that a value of n lies between 1 and 1.6 for hard materials and for soft materials it is above 1.6. Thus the ninhydrin comes under the soft materials category. Since the value of n is greater than 2, the hardness of the material is found to increase with the increase of load confirming the prediction of Onitsch [35]. A plot of P/d against d (Fig. 8c) drawn following proportional specimen resistance (PSR) model will be a straight line, the slope of which gives the load independent microhardness [36]. The load independent microhardness value is calculated from the slope (P/d2 ), which, when multiplied by Vicker’s conversion factor 1.8544 gives 37 kg/mm2 for ninhydrin. 3.6. Thermal analysis Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) of ninhydrin were carried out simultaneously employing NETZCH STA 409 Thermal Analyzer are shown in Fig. 9. 1.88 mg of ninhydrin was taken and heated at a rate of 20 ◦ C/min in inert nitrogen atmosphere. There is a sharp weight loss with the maximum at about 146 ◦ C. It is due to loss of water of crystallization. This weight loss is followed by a major weight loss pattern between 155 and 254 ◦ C due to melting of the compound. There is a sharp endotherm with a maximum at 146 ◦ C. It coincides with the first stage of weight loss in the TGA trace. There is one sharper endotherm at 248.98 ◦ C. This endotherm is assigned to melting of the compound, which is close to the value reported earlier [15]. The sharpness of the thermogram is also illustrative of the crystal purity without association of any impurities [37,38]. 3.7. Fluorescence studies Fluorescence finds wide application in the branches of biochemical, medical, and chemical research fields, for analyzing organic
Fig. 10. (a) Excitation spectrum and (b) emission spectrum.
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compounds. Fluorescence may be expected generally in molecules that are aromatic or contain multiple conjugated double bonds with a high degree of resonance stability [39]. Hence the excitation and emission spectra for ninhydrin were recorded using FP-6500 Spectrofluorometer. The excitation spectrum was recorded in the range 220–350 nm and the sample was excited at 290 nm (Fig. 10a). The emission spectrum was measured in the range 350–540 nm. Peaks at 450 and 470 nm were observed in the emission spectrum (Fig. 10b). The results indicate that ninhydrin crystal has a blue fluorescence emission. 4. Conclusion Optically good quality single crystal of ninhydrin was grown using temperature reduction technique. Single crystal X-ray diffraction study shows that ninhydrin crystallizes in a monoclinic system. A multicrystal X-ray diffractometer study reveals the crystalline perfection of the crystal without any internal structural grain boundaries. FTIR spectrum recorded in the range of 400–4000 cm−1 indicates the vibrational frequencies of the functional group such as aromatic C–H stretching, OH vibrations and carbonyl (C O) stretching. Optical transmission studies confirm that ninhydrin is transparent in the entire visible region and the band gap energy is 2.5 eV. Microhardness measurements imply that the ninhydrin comes under the soft materials category. TGA reveals that the sample is thermally stable and has higher melting point. The Kurtz powder studies on the NLO property showed that the second harmonic conversion efficiency is about five times that of KDP. References [1] C.K. Lakshmana Perumal, A. Arulchakkaravarthi, N.P. Rajesh, P. Santhana Raghavan, Y.C. Huang, M. Ichimura, P. Ramasamy, J. Cryst. Growth 240 (2002) 212–217. [2] C.W. Tang, S.A. Van Slyke, Appl. Phys. Lett. 51 (1987) 913–915. [3] L.R. Dalton, Pure Appl. Chem. 76 (2004) 1421–1433. [4] K. Jagannathan, S. Kalainathan, T. Gnanasekaran, N. Vijayan, G. Bhagavannarayana, Cryst. Res. Technol. 42 (2007) 483–487. [5] C. Mondini, A. Monedero, L. Leita, G. Bragato, M. De Nobili, Commun. Soil Sci. Plant Anal. 28 (1997) 113–122. [6] D.B. Hansen, M.M. Joullié, Chem. Soc. Rev. 34 (2005) 408–417.
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