ARTICLE IN PRESS

Journal of Crystal Growth 303 (2007) 520–524 www.elsevier.com/locate/jcrysgro

Second harmonic generation and crystal growth of new chalcone derivatives P.S. Patila,, S.M. Dharmaprakasha,, K. Ramakrishnab, Hoong-Kun Func, R. Sai Santosh Kumard, D. Narayana Raod a

Department of Studies in Physics, Mangalore University, Mangalagangotri, Mangalore 574 199, India Department of Materials Science, Mangalore University, Mangalagangotri, Mangalore 574 199, India c X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia d School of Physics, University of Hyderabad, Hyderabad 500 046, India b

Received 12 October 2006; received in revised form 14 December 2006; accepted 15 December 2006 Communicated by M. Schieber Available online 3 February 2007

Abstract We report on the synthesis, crystal structure and optical characterization of chalcone derivatives developed for second-order nonlinear optics. The investigation of a series of five chalcone derivatives with the second harmonic generation powder test according to Kurtz and Perry revealed that these chalcones show efficient second-order nonlinear activity. Among them, high-quality single crystals of 3-Br-40 methoxychalcone (3BMC) were grown by solvent evaporation solution growth technique. Grown crystals were characterized by X-ray powder diffraction (XRD), laser damage threshold, UV–vis–NIR and refractive index measurement studies. Infrared spectroscopy, thermogravimetric analysis and differential thermal analysis measurements were performed to study the molecular vibration and thermal behavior of 3BMC crystal. Thermal analysis does not show any structural phase transition. r 2007 Elsevier B.V. All rights reserved. PACS: 61.50; 81.10; 42.65 Keywords: A1. Characterization; A1. Laser damage threshold; A1. X-ray powder diffraction; A2. Growth from solutions; A2. Single-crystal growth; B1. Organic compounds; B2. Nonlinear optical materials

1. Introduction There is currently a considerable effort to develop new organic materials with large second-order nonlinear optical (NLO) susceptibilities because of their potential applications in optical signal processing and frequency conversion [1–5]. For NLO materials with large second-order nonlinearities, noncentrosymmetry at both the molecular and the macroscopic level is a prerequisite for nonvanishing molecular hyperpolarizabilities b and macroscopic susceptibilities w(2). Among NLO materials, organic NLO materials are attracting a great deal of attention, as they have Corresponding authors. Tel.: +91 8242287363; fax: +91 8242287367.

E-mail addresses: [email protected] (P.S. Patil), [email protected] (S.M. Dharmaprakash). 0022-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2006.12.068

large optical susceptibilities, inherent ultrafast response times, and high optical thresholds for laser power as compared with inorganic materials. It has been generally understood that the second-order molecular nonlinearity can be enhanced by large delocalized p-electron systems with strong donor and acceptor groups [6,7]. Since a large molecular hyperpolarizability b is the basis of a strong second harmonic generation (SHG) response, organic molecules with long conjugation systems that usually exhibit large b values are certainly candidate molecules for NLO materials. Many highly nonlinear materials such as 3-methyl-4-methoxy-40 -nitrostilbene (MMONS) [8], 4-bromo-40 -methoxychalcone (BMC) [9], etc. have been found according to this simple principle. A strong macroscopic second-order nonlinearity requires not only a large b value but also a noncentrosymmetric

ARTICLE IN PRESS P.S. Patil et al. / Journal of Crystal Growth 303 (2007) 520–524

crystal structure. Unfortunately, only a few molecules with large b values crystallize in noncentrosymmetric structure, and fewer of them are useful for NLO materials. Many approaches have been tried to overcome this problem, e.g., designing molecules with small ground-state dipole moments [10], choosing pure enantiomers [11], using inclusion complexes and introducing chirality [12] or an octupole [13] in the molecules. Recently, during our systematic search for NLO materials we have found that chalcone derivatives, viz. 4-OCH3-40 -nitrochalcone [14] and 3,4-di-OCH3-40 methoxychalcone [15], can easily be crystallized into noncentrosymmetric structures and thus exhibit SHG conversion efficiency of about 5 and 15 times than that of urea, respectively. Thus, these compounds not only have large b values but also usually have fairly strong powder SHG. In the present investigation, we report the synthesis and SHG of five chalcone derivatives. We have also reported for the first time the bulk growth, X-ray powder diffraction (XRD), optical, thermal and laser damage studies of 3BMC.

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The schematic diagram of the preparation of chalcones is shown in Scheme 1. 2.2. Melting point measurement The melting points were determined by capillary tube method and are uncorrected. It should be noted that chalcone derivatives show a high melting point exceeding 174 1C [14]. Most organic compounds reported to have high SHG efficiency to date show relatively low melting points: MNA, 131 1C [7]; N-(4-nitrophenyl)-(L)-prolinol (NPP), 116 1C [23]; 2-(a-methylbenzylamino)-5-nitropyridine (MBANP), 83 1C [25]. However 3BMC and TMBC have high melting points (126, 148 1C) compared with other organic materials with high nonlinearity. These high melting points are favorable in device applications. 2.3. UV–vis–NIR absorption

2. Synthesis and characterization

For optical application, especially for SHG, the material considered must be transparent in the wavelength region of interest. The UV–vis–NIR absorption spectra were made using acetone in the wavelength range of 200–1000 nm, and corresponding cutoff wavelengths are listed in Table 1.

2.1. Synthesis of chalcones

2.4. Measurement of SHG efficiency

Following the literature, we synthesized the derivatives of chalcone disubstituted with donor–acceptor substituents [16]. The crude product was recrystallized with acetone. For example, in case of 3-Br-40 -methoxychalcone, 3-bromobenzaldehyde (0.01 mol) and 4-methoxyacetophenone (0.01 mol) were stirred in 60 ml of ethanol at room temperature. Ten milliliters of 10% of NaOH aqueous solution was added and the mixture was stirred for 2 h. The precipitate was filtered, washed with water, dried and the crude product recrystallized twice from acetone.

The SHG efficiencies of the chalcone derivatives were measured with the powder method developed by Kurtz and Perry [17]. The powder sample with an average particle size of 100–150 mm packed in a microcapillary of uniform bore was exposed to laser radiations of a Q-switched Nd:YAG laser beam (1064 nm, 8 mJ, 8 ns, 10 Hz). The SHG was confirmed by the emission of green radiation and the parent ray was filtered using IR filter. The amplitude of the SHG output voltage was measured using photomultiplier and digitalizing oscilloscope assembly. A sample of urea, also powdered to the same particle size as the experimental sample, was used as a reference material for the present measurement. The measured SHG values are listed in Table 1. The SHG efficiencies of some NLO crystals are given in Table 2. 2.5. Single-crystal XRD

Scheme 1. Synthesis of chalcone derivatives (3).

Although the preliminary focus of this study is on the molecular quadratic NLO responses of the new chalcone derivatives, the investigation of their bulk NLO properties is obviously of great importance. However, the possibilities for such studies are clearly somewhat limited by our ability to force the compounds to crystallize in a favorable noncentrosymmetric structure. We have obtained singlecrystal structures for all the compounds and their unit cell parameters, crystal systems and space groups; these are represented in Table 1. The detail structural analysis and results can be found in our earlier publications [18–22]. All compounds studied crystallize noncentrosymmetrically,

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Table 1 Crystal system, space group, unit cell parameters, SGH values, cutoff wavelengths and melting points of five chalcone derivatives Code

R1

R2

Crystal system and space group

Powder SHG (X urea)

lcutoff (nm)

Tm (1C)

3BMC

4-OCH3

3-Br

Monoclinic P21 a ¼ 10.2917(1) A˚ b ¼ 3.8970(1) A˚ c ¼ 17.0919(2) A˚ Z¼2

2

416

126

DCBC

4-Br

2,4-Di-Cl

Orthorhombic P212121 a ¼ 11.4642(4) A˚ b ¼ 30.0972(10) A˚ c ¼ 3.9020(1) A˚

1.5

430

90

Z¼4 DCMLC

4-CH3

2,4-Di-Cl

Orthorhombic Pna21 a ¼ 28.3884(5) A˚ b ¼ 3.9343(1) A˚ c ¼ 12.0092(2) A˚ Z¼4

0.85

418

100

TMBC

4-Br

2,4,5-Tri-OCH3

Orthorhombic P212121 a ¼ 7.3031(3) A˚ b ¼ 10.3422(4) A˚

1.8

474

148

4.3

472

132

c ¼ 21.3355(9) A Z¼4 TMCC

4-Cl

2,4,5-Tri-OCH3

Orthorhombic P212121 a ¼ 7.0295(4) A˚ b ¼ 10.5127(6) A˚ c ¼ 22.2438(13) A Z¼4

Table 2 Properties of some organic nonlinear crystals Name

Powder SHG (X urea)

Melting point (1C)

Cutoff wavelength (nm)

Reference

MNA BMC MNC NPP MNP MBANP

22 10.7 5 154 10 25

131 159.5 174 116 69 83

521 380 415 505 490 450

[7] [9] [14] [23] [24] [25]

highlighting the easy in obtaining materials suitable for bulk NLO effects. 3. Crystal growth and characterization studies

temperature. The solution was prepared in a vessel covered with perforated sheet and kept in a dust-free atmosphere. At the period of super saturation, tiny crystals were nucleated. They were allowed to grow to maximum possible dimension and then harvested. Thus grown transparent crystals are shown in Fig. 1. 3.2. FTIR FTIR spectrum provides more information about the structure of a compound. In this technique, almost all functional groups in a molecule absorb a definite range of frequency. The absorption of IR radiation causes the various bands in a molecule to stretch and bend with respect to one another. The FTIR spectrum of the compound is shown in Fig. 2. The position of various bond vibrations of 3BMC is given in Table 3.

3.1. Crystal growth 3.3. X-ray powder diffraction 3BMC does not dissolve in water but in organic solvents such as acetone, ethanol, methanol, etc. We found that acetone was the best solvent for this crystal growth. The crystal was grown by slow evaporation technique at room

X-ray powder diffraction measurements were made on a Bruker D8 Advance X-ray diffractometer operated at 30 kV and 20 mA, using the (y, y) geometry at a scan speed

ARTICLE IN PRESS P.S. Patil et al. / Journal of Crystal Growth 303 (2007) 520–524

Fig. 1. Photograph of 3-Br-40 -methoxychalcone crystals grown from solvent evaporation solution growth technique.

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Fig. 3. Powder X-ray diffraction pattern of 3-Br-40 -methoxychalcone.

Fig. 4. TGA and DTA curves of 3-Br-40 -methoxychalcone. 0

Fig. 2. Infrared spectra of 3-Br-4 -methoxychalcone.

3.4. Thermo-gravimetric and differential thermal analysis (TG–DTA) Table 3 Position of various bond vibrations of 3-Br-40 -methoxychalcone 1

Wave number (cm )

Assignment

3058 2933 1660 1602 1465 1257 829, 777, 661

Aromatic proton stretching Aliphatic protons stretching CQO (carbonyl) stretching CQC stretching CH3 bending (C–H-deformation) C–O structure Out of plane, C–H bending

of 11/min. The data were collected using Ni-filtered Cu-target tube at room temperature in the 2y range of 15–601. The lines were indexed using Powder X software by providing lattice parameters as a ¼ 10.2917 A˚, b ¼ 3.8970 A˚ and c ¼ 17.0919 A˚ with b ¼ 107.3131 [18]. The XRD pattern of 3-Br-40 -methoxychalcone is shown in Fig. 3. The sharpness of the peaks shows good degree of crystallinity.

DTA and TGA of 3BMC crystals were carried out using apparatus STA 409C thermal analyzer. The sample was heated at a rate of 10 1C/min in inert nitrogen atmosphere. Fig. 4 shows the thermogram for DTA and TGA of 3BMC. The DTA curve shows a major endothermic peak, which corresponds to the melting point of the compound at 126 1C, after which the compound decomposes into a sticky viscous substance. At higher temperatures, this decomposition process continues up to 700 1C with the removal of almost the entire compound as gaseous products. The sharpness of the endothermic peak shows good degree of crystallinity of the grown ingot. 3.5. Optical damage threshold The optical damage threshold of an optic crystal is an important factor that affects its applications. Although LiNbO3 has many excellent properties: piezoelectricity, and high EO and nonlinear optical coefficients, the low damage

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Table 4 Laser damage threshold of some NLO crystals Compound

Laser damage threshold (GW/cm2)

KDP Urea BBO LAP Benzimidazole MNC 3BMCa

0.20 1.50 5.0 10 1.71 0.99 0.57

KDP, potassium dihydrogen phosphate; BBO, beta-barium borate; LAP, 0 L-arginine phosphate; MNC, 4-OCH3-4 -nitrochalcone. a Present work.

threshold of LiNbO3 severely limits its application. Therefore, a practical EO crystal should possess a sufficiently high optical damage threshold. Optical damage threshold studies have been carried out for the solution grown 3BMC single crystal using Qswitched Nd:YAG laser of pulse width 6 ns at a wavelength of 1064 nm and 10 Hz repetition rate operating in TEM00 mode is used as the source. The beam of the laser was focused, and the sample was moved step by step into the focus along the optical axis of the crystal. In the present study, laser damage was found to be 0.57 GW/cm2. From this analysis we came to know that the laser damage threshold value of 3BMC single crystal is higher than KDP and lower than MNC single crystal. The laser damage threshold of some NLO crystals are given in Table 4 [14]. The high damage threshold contributes to attractiveness of the present compound in practical applications. Furthermore, it is important to note that the present compound is sufficiently chemically stable, and not hygroscopic or soluble in water. It should be noted that keto conjugate compounds usually exhibit these features. 3.6. Refractive index The refractive index of the crystal was determined by the Brewster’s angle method using the equation n ¼ tan yP, where yP is the polarizing angle. The measured refractive index of the crystal is 1.61 (He–Ne laser, l ¼ 632.8 nm). 4. Conclusions The compounds studied crystallize noncentrosymmetrically, highlighting the materials suitable for bulk NLO effects. Optical quality single crystal of 3BMC was grown using a solvent evaporation solution growth technique. The UV–vis–NIR spectrum elucidates that the crystal is transparent in the visible region. FTIR and X-ray diffraction studies confirm the identity of the synthesized material. DTA and TGA analysis has revealed that 3BMC is stable up to 126 1C; after that, it undergoes a physical transformation associated with mass changes. Thus, during thermal treatment, the possibility of any change in crystal

structure of the original compound is ruled out. The laser damage study shows the crystal as having moderate damage threshold. The refractive index for 3BMC has been reported. The relative SHG efficiency of the material is two times greater than that of urea. Based on these facts, it could be proposed that this novel material can be better accommodated for optical applications. Acknowledgments PSP thanks Defence Research Development Organization (DRDO), Government of India, for Junior Research Fellowship (JRF). Authors would like to thank Professor M. Pattabi, Chairman, Department of Materials Science, Mangalore University, Mangalagangotri, for providing the powder XRD facility. References [1] C. Bosshard, K. Sutter, P. Prgtre, J. Hulliger, M. Florsheimer, P. Kaatz, P. Gunter, Organic Nonlinear Optical Materials, Gordon and Breach Science Publishers, Amsterdam, 1995. [2] J. Zyss, Molecular Nonlinear Optics: Materials, Physics, Deuices, Academic Press, Boston, 1994. [3] P. N Prasad, J.D. Williams, Introduction to Nonlinear Optical Effects in Molecules and Polymers, Wiley, New York, 1990. [4] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, Orlando, FL, 1987. [5] C. Bosshard, K. Sutter, R. Schlesser, P. Gunter, J. Opt. Soc. Am. B 10 (1993) 867. [6] J. Zyss, Chem. Phys. 71 (1979) 909. [7] B.F. Levine, C.G. Bethea, C.D. Thurmond, R.T. Lynch, J.L. Berstein, J. Appl. Phys. 50 (1979) 2523. [8] J.D. Bierlein, L.K. Cheng, Y. Wang, W. Tam, Appl. Phys. Lett. 56 (1990) 423. [9] G.J. Zhang, T. Kinoshita, K. Sasaki, Y. Goto, M. Nakayama, J. Crystal Growth 100 (1990) 411. [10] J. Zyss, D.S. Chemla, J. Chem. Phys. 74 (1981) 4800. [11] J. Oudar, R. Hieple, J. Appl. Phys. 48 (1977) 2699. [12] Y. Wang, D.F. Eaton, Chem. Phys. Lett. 120 (1985) 441. [13] J. Zyss, I. Ledoux, Chem. Rev. 94 (1994) 77. [14] P.S. Patil, S.M. Dharmaprakash, H.-K. Fun, M.S. Karthikeyan, J. Crystal Growth 297 (2006) 111. [15] V. Shettigar, P.S. Patil, S. Naveen, S.M. Dharmaprakash, M.A. Sridhar, J. Shashidhara Prasad, J. Crystal Growth 245 (2006) 44. [16] E.P. Kohler, H.M. Chadwell, in: Organic Syntheses Coll., vol. 1, Wiley, New York, 1941, p. 78. [17] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798. [18] P.S. Patil, M.M. Rosli, H.-K. Fun, I.A. Razak, V.G. Puranik, S.M. Dharmaprakash, Acta Crystallogr. E 62 (2006) 04798. [19] P.S. Patil, J.B.J. Teh, H.-K, Fun, I.A. Razak, S.M. Dharmaprakash, Acta Crystallogr. E 62 (2006) 01710. [20] P.S. Patil, J.B.J. Teh, H.-K. Fun, I.A. Razak, S.M. Dharmaprakash, Acta Crystallogr. E 62 (2006) 03096. [21] P.S. Patil, M.M. Rosli, H.-K. Fun, I.A. Razak, S.M. Dharmaprakash, Acta Crystallogr. E 62 (2006) 04644. [22] P.S. Patil, S.-L. Ng, I.A. Razak, H.-K. Fun, S.M. Dharmaprakash, Acta Crystallogr. E 62 (2006) 04448. [23] J. Zyss, J.F. Nicoud, M. Coquillay, J. Chem. Phys. 81 (1984) 4160. [24] J.-L. Oudar, R. Hierle, J. Appl. Phys. 48 (1977) 2699. [25] R. Twieg, A. Azema, K. Jian, Y.Y. Cheng, Chem. Phys. Lett. 92 (1982) 208.