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Synthesis, growth and characterization of second-order nonlinear optical crystal: 5-Br-2-thienyl-4′-methoxychalcone
ARTICLE IN PRESS
Journal of Crystal Growth 305 (2007) 218–221 www.elsevier.com/locate/jcrysgro
Synthesis, growth and characterization of second-order nonlinear optical crystal: 5-Br-2-thienyl-40-methoxychalcone P.S. Patil, S.M. Dharmaprakash Department of Studies in Physics, Mangalore University, Mangalagangotri, Mangalore-574 199, India Received 23 January 2007; received in revised form 11 April 2007; accepted 13 April 2007 Available online 24 April 2007
Abstract Single crystals of 5-Br-2-thienyl-40 -methoxychalcone were grown by slow evaporation solution growth technique at room temperature. The crystal system has been confirmed from the powder X-ray diffraction analysis. Optical behavior such as UV–vis–NIR absorption spectra, and second harmonic generation were investigated to explore the NLO characteristics of the material. The laser damage threshold has been measured by using Q-switched Nd:YAG laser. The observed value is greater than that of KDP. r 2007 Elsevier B.V. All rights reserved. PACS: 61.10.Nz; 81.10.Dn; 77.84.Fa; 78.40.q Keywords: A1. X-ray powder diffraction; A2. Growth from solutions; B1. Chalcone derivatives; B2. Nonlinear optical materials
1. Introduction Chalcone derivatives with various combinations of terminal electron donor and/or acceptor groups have been the object of a continuous interest over the past two decades, particularly in view of their large molecular hyperpolarizabilities and good crystallizability [1–5], which may lead to a wide range of applications in integrated optics (second harmonic generation (SHG), frequency mixing, electro-optic modulation, parametric effects, etc.) [6,7]. In these materials, the CQO bond acts as the electron-withdrawing group, and electron-rich substituents on the aromatic rings serve as the electron-donating group, forming a so-called D—p- - - A type molecule. In previous papers [3–5], we reported crystal growth of new nonlinear optical chalcone derivatives: 3,4-dimethoxy40 -methoxychalcone (DMMC), 4-methoxy-40 -nitrochalcone (MNC) and 3-bromo-40 -methoxychalcone (3BMC). The study of their SHG gave a first insight into tuning of the NLO behavior with terminal substitution. It appeared that methoxy end substitutions favor the occurrence of noncentrosymmetric crystal system. Moreover, it has been Corresponding author. Tel.: +91 8242287363; fax: +91 8242287367.
E-mail address: [email protected] (P.S. Patil). 0022-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2007.04.038
demonstrated that nitro substitution group increases crystal thermal stability. In this paper, we report the growth of 5-Br-2-thienyl-40 methoxychalcone (5Br2ThMC) and its characterization by powder X-ray diffraction (PXRD), UV–vis–NIR, SHG measurement and laser damage studies. The SHG conversion efficiency is greater than that of MNC (5 U) [4] and 3BMC (2 U) [5] single crystals.
2. Experimental procedure 2.1. Synthesis Commercially available 5-bromothiophene-2-carbaldehyde and 4-methoxyacetophenone were used as supplied. 5-Br-2-thienyl-40 -methoxychalcone was prepared by Claisen–Schmidt condensation method [5]. This is a reaction of substituted acetophenone with substituted benzaldehyde in the presence of an alkali. Aqueous solution of sodium hydroxide (5%, 10 ml) was added slowly with stirring to a mixture of 5-bromothiophene-2-carbaldehyde (0.01 mol) and 4-methoxyacetophenone (0.01 mol) in ethanol (60 ml). After stirring for 4 h, the reaction mixture was poured on to ice-cold water (250 ml) and kept aside for 12 h. The
ARTICLE IN PRESS P.S. Patil, S.M. Dharmaprakash / Journal of Crystal Growth 305 (2007) 218–221
219
precipitated solid was filtered, dried and recrystallized from acetone. The schematic diagram of the synthesis of 5Br2ThMC is shown in Scheme 1. 2.2. Melting point Melting point was determined by open capillary method and is uncorrected. 5Br2ThMC has a high melting point (141 1C) as compared to DMMC [3]. This high melting point is favorable in device applications. 2.3. Crystal growth Selection of suitable solvents is very definitive for the growth of good-quality single crystals [8]. 5Br2ThMC is insoluble in water, and soluble in acetone, N,N-dimethylformamide (DMF), chloroform, etc. We found that acetone was the best solvent for this crystal growth. The filtered solution (Whatman filter paper) of 5Br2ThMC prepared in acetone was transferred to a crystal growth vessel, and crystallization was allowed to take place by slow evaporation at room temperature (27 1C). Welldefined, transparent crystals were obtained within 2 weeks (Fig. 1).
Fig. 1. Photograph of 5-Br-2-thienyl-40 -methoxychalcone crystals.
3. Results and discussion 3.1. X-ray powder diffraction The PXRD study was carried out to confirm the crystal system of the compound using a Bruker D8 Advance X-ray diffractometer with Cu Ka radiation (l ¼ 1.5418 A˚). The sample was scanned at a rate of 11 per minute in the range 10–501 (Fig. 2). The diffraction pattern has been indexed by least-square fit method. 5Br2ThMC belongs to orthorhombic crystal system and the lattice parameters are: a ¼ 10.1774 A˚, b ¼ 31.8924 A˚ and c ¼ 3.9078 A˚ [9]. The
Fig. 2. Powder X-ray diffraction pattern of 5-Br-2-thienyl-40 -methoxychalcone.
X-ray diffraction pattern has the highest intensity corresponding to (2 2 0) plane.
3.2. Second harmonic generation
Scheme 1. Synthesis of 5-bromo-2-thienyl-40 -methoxychalcone.
In order to measure the properly optimized output intensity, it is desired that the crystal should be cut at a particular axis with respect to its optical axis. However, in the present measurement, we could not follow this method due to the fine needle shaped nature of the crystallites. The
ARTICLE IN PRESS P.S. Patil, S.M. Dharmaprakash / Journal of Crystal Growth 305 (2007) 218–221
220
Table 1 Nonlinear optical properties of chalcone derivatives single crystals Name
Molecular structures
BMC
O
Melting point (1C)
Cutoff (nm)
Reference
2
159.5
380
[2]
15
83
450
[3]
5
174
415
[4]
10.5
141
430
Present
Br
H3CO
DMMC
Powder SHG ( urea)
O
OCH3
H3CO OCH3
MNC
O
OCH3
O 2N
5Br2ThMC
O S Br H3CO
SHG measurement was performed according to Kurtz and Perry [10] using 8 ns pulsed Q-switched Nd: YAG laser at 1064 nm wavelength (Beam energy-4.0 mJ). The powder sample with an average particle size of 100–150 mm packed in a microcapillary of uniform bore was exposed to laser radiations. The second harmonic (SH) radiation at 532 nm obtained at the output was filtered using a SH separator to remove the fundamental input radiation. 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. Table 1 shows the SHG efficiencies of various chalcone derivatives. It is clearly ascertained that 5-Br-2-thienyl-40 -methoxychalcone display very high efficiency (10.5 U) relative to urea. This strongly suggests that the compound has potential SHG applications. 3.3. Laser damage
Fig. 3. UV–vis absorption spectrum of 5-Br-2-thienyl-40 -methoxychalcone.
Optical damage threshold studies have been carried out for the solution grown 5-Br-2-thienyl-40 -methoxychalcone single crystal, using Q-switched Nd: YAG laser of pulse width 6 ns at a wavelength of 1064 nm and 10 Hz repetition rate operating in TEM00 mode. 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 0.67 GW/cm2. From this analysis, we came to know that the laser damage
threshold value of 5-Br-2-thienyl-40 -methoxychalcone single crystal is higher than that of KDP (0.2 GW/cm2) and lower than that of urea (1.50 GW/cm2) and MNC (0.9 GW/cm2) single crystals [4]. 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 neither hygroscopic nor soluble in water.
ARTICLE IN PRESS P.S. Patil, S.M. Dharmaprakash / Journal of Crystal Growth 305 (2007) 218–221
221
3.4. UV–vis–NIR absorption
Acknowledgments
Good transparency is also one of the important properties for a useful second-order nonlinear optical material. The UV–vis–NIR absorption spectra were recorded on a SHIMADZU 1601 UV spectrometer using an acetone solution and a quartz cell with a length of 10 mm. The cutoff wavelength is listed in Table 1. There was no absorption at the wavelength of SH (532 nm) (as shown in Fig. 3).
PSP thanks Defence Research Development Organization (DRDO), Government of India, for a Junior Research Fellowship (JRF). The authors are grateful to Professor M. Pattabi, Department of Materials Science, Mangalore University, Mangalagangotri, for providing the Powder XRD facility.
4. Conclusions 5-Br-2-thienyl-40 -methoxychalcone was synthesized and crystals were grown by slow-evaporation solution method at room temperature. Melting point of the crystal is moderately good. Lattice parameters have been calculated from PXRD studies. The relative SHG efficiency of the material is greater than that of urea. The UV–vis–NIR result elucidates that the crystal may find useful optical applications in the transparent wavelength window region 430–1100 nm. Furthermore, laser damage threshold was found to be 0.67 GW/cm2 for 1064 nm wavelength.
References [1] Y. Goto, A. Hayashi, Y. Kimura, M. Nakayama, J. Crystal Growth 108 (1991) 688. [2] G. Zhang, T. Kinoshita, K. Sasaki, Y. Goto, M. Nakayama, J. Crystal Growth 100 (1990) 411. [3] V. Shettigar, P.S. Patil, S. Naveen, S.M. Dharmaprakash, M.A. Sridhar, J. Shashidhara Prasad, J. Crystal Growth 245 (2006) 44. [4] P.S. Patil, S.M. Dharmaprakash, H.-K. Fun, M.S. Karthikeyan, J. Crystal Growth 297 (2006) 111. [5] P.S. Patil, S.M. Dharmaprakash, K. Ramakrishna, H.-K. Fun, R. Sai Santosh Kumar, D. Narayana Rao, J. Crystal Growth 303 (2007) 520. [6] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, vol. 1–2, Academic Press, New York, 1987. [7] J. Zyss, Molecular Nonlinear Optics, Academic Press, Boston, 1993. [8] J.N. Sherwood, Pure Appl. Opt. 7 (1998) 229. [9] P.S. Patil, S.-L. Ng, I.A. Razak, H.-K. Fun, S.M. Dharmaprakash, Acta Crystallogr. Sect. E 63 (2007) o59. [10] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798.
Journal of Crystal Growth 305 (2007) 218–221 www.elsevier.com/locate/jcrysgro
Synthesis, growth and characterization of second-order nonlinear optical crystal: 5-Br-2-thienyl-40-methoxychalcone P.S. Patil, S.M. Dharmaprakash Department of Studies in Physics, Mangalore University, Mangalagangotri, Mangalore-574 199, India Received 23 January 2007; received in revised form 11 April 2007; accepted 13 April 2007 Available online 24 April 2007
Abstract Single crystals of 5-Br-2-thienyl-40 -methoxychalcone were grown by slow evaporation solution growth technique at room temperature. The crystal system has been confirmed from the powder X-ray diffraction analysis. Optical behavior such as UV–vis–NIR absorption spectra, and second harmonic generation were investigated to explore the NLO characteristics of the material. The laser damage threshold has been measured by using Q-switched Nd:YAG laser. The observed value is greater than that of KDP. r 2007 Elsevier B.V. All rights reserved. PACS: 61.10.Nz; 81.10.Dn; 77.84.Fa; 78.40.q Keywords: A1. X-ray powder diffraction; A2. Growth from solutions; B1. Chalcone derivatives; B2. Nonlinear optical materials
1. Introduction Chalcone derivatives with various combinations of terminal electron donor and/or acceptor groups have been the object of a continuous interest over the past two decades, particularly in view of their large molecular hyperpolarizabilities and good crystallizability [1–5], which may lead to a wide range of applications in integrated optics (second harmonic generation (SHG), frequency mixing, electro-optic modulation, parametric effects, etc.) [6,7]. In these materials, the CQO bond acts as the electron-withdrawing group, and electron-rich substituents on the aromatic rings serve as the electron-donating group, forming a so-called D—p- - - A type molecule. In previous papers [3–5], we reported crystal growth of new nonlinear optical chalcone derivatives: 3,4-dimethoxy40 -methoxychalcone (DMMC), 4-methoxy-40 -nitrochalcone (MNC) and 3-bromo-40 -methoxychalcone (3BMC). The study of their SHG gave a first insight into tuning of the NLO behavior with terminal substitution. It appeared that methoxy end substitutions favor the occurrence of noncentrosymmetric crystal system. Moreover, it has been Corresponding author. Tel.: +91 8242287363; fax: +91 8242287367.
E-mail address: [email protected] (P.S. Patil). 0022-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2007.04.038
demonstrated that nitro substitution group increases crystal thermal stability. In this paper, we report the growth of 5-Br-2-thienyl-40 methoxychalcone (5Br2ThMC) and its characterization by powder X-ray diffraction (PXRD), UV–vis–NIR, SHG measurement and laser damage studies. The SHG conversion efficiency is greater than that of MNC (5 U) [4] and 3BMC (2 U) [5] single crystals.
2. Experimental procedure 2.1. Synthesis Commercially available 5-bromothiophene-2-carbaldehyde and 4-methoxyacetophenone were used as supplied. 5-Br-2-thienyl-40 -methoxychalcone was prepared by Claisen–Schmidt condensation method [5]. This is a reaction of substituted acetophenone with substituted benzaldehyde in the presence of an alkali. Aqueous solution of sodium hydroxide (5%, 10 ml) was added slowly with stirring to a mixture of 5-bromothiophene-2-carbaldehyde (0.01 mol) and 4-methoxyacetophenone (0.01 mol) in ethanol (60 ml). After stirring for 4 h, the reaction mixture was poured on to ice-cold water (250 ml) and kept aside for 12 h. The
ARTICLE IN PRESS P.S. Patil, S.M. Dharmaprakash / Journal of Crystal Growth 305 (2007) 218–221
219
precipitated solid was filtered, dried and recrystallized from acetone. The schematic diagram of the synthesis of 5Br2ThMC is shown in Scheme 1. 2.2. Melting point Melting point was determined by open capillary method and is uncorrected. 5Br2ThMC has a high melting point (141 1C) as compared to DMMC [3]. This high melting point is favorable in device applications. 2.3. Crystal growth Selection of suitable solvents is very definitive for the growth of good-quality single crystals [8]. 5Br2ThMC is insoluble in water, and soluble in acetone, N,N-dimethylformamide (DMF), chloroform, etc. We found that acetone was the best solvent for this crystal growth. The filtered solution (Whatman filter paper) of 5Br2ThMC prepared in acetone was transferred to a crystal growth vessel, and crystallization was allowed to take place by slow evaporation at room temperature (27 1C). Welldefined, transparent crystals were obtained within 2 weeks (Fig. 1).
Fig. 1. Photograph of 5-Br-2-thienyl-40 -methoxychalcone crystals.
3. Results and discussion 3.1. X-ray powder diffraction The PXRD study was carried out to confirm the crystal system of the compound using a Bruker D8 Advance X-ray diffractometer with Cu Ka radiation (l ¼ 1.5418 A˚). The sample was scanned at a rate of 11 per minute in the range 10–501 (Fig. 2). The diffraction pattern has been indexed by least-square fit method. 5Br2ThMC belongs to orthorhombic crystal system and the lattice parameters are: a ¼ 10.1774 A˚, b ¼ 31.8924 A˚ and c ¼ 3.9078 A˚ [9]. The
Fig. 2. Powder X-ray diffraction pattern of 5-Br-2-thienyl-40 -methoxychalcone.
X-ray diffraction pattern has the highest intensity corresponding to (2 2 0) plane.
3.2. Second harmonic generation
Scheme 1. Synthesis of 5-bromo-2-thienyl-40 -methoxychalcone.
In order to measure the properly optimized output intensity, it is desired that the crystal should be cut at a particular axis with respect to its optical axis. However, in the present measurement, we could not follow this method due to the fine needle shaped nature of the crystallites. The
ARTICLE IN PRESS P.S. Patil, S.M. Dharmaprakash / Journal of Crystal Growth 305 (2007) 218–221
220
Table 1 Nonlinear optical properties of chalcone derivatives single crystals Name
Molecular structures
BMC
O
Melting point (1C)
Cutoff (nm)
Reference
2
159.5
380
[2]
15
83
450
[3]
5
174
415
[4]
10.5
141
430
Present
Br
H3CO
DMMC
Powder SHG ( urea)
O
OCH3
H3CO OCH3
MNC
O
OCH3
O 2N
5Br2ThMC
O S Br H3CO
SHG measurement was performed according to Kurtz and Perry [10] using 8 ns pulsed Q-switched Nd: YAG laser at 1064 nm wavelength (Beam energy-4.0 mJ). The powder sample with an average particle size of 100–150 mm packed in a microcapillary of uniform bore was exposed to laser radiations. The second harmonic (SH) radiation at 532 nm obtained at the output was filtered using a SH separator to remove the fundamental input radiation. 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. Table 1 shows the SHG efficiencies of various chalcone derivatives. It is clearly ascertained that 5-Br-2-thienyl-40 -methoxychalcone display very high efficiency (10.5 U) relative to urea. This strongly suggests that the compound has potential SHG applications. 3.3. Laser damage
Fig. 3. UV–vis absorption spectrum of 5-Br-2-thienyl-40 -methoxychalcone.
Optical damage threshold studies have been carried out for the solution grown 5-Br-2-thienyl-40 -methoxychalcone single crystal, using Q-switched Nd: YAG laser of pulse width 6 ns at a wavelength of 1064 nm and 10 Hz repetition rate operating in TEM00 mode. 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 0.67 GW/cm2. From this analysis, we came to know that the laser damage
threshold value of 5-Br-2-thienyl-40 -methoxychalcone single crystal is higher than that of KDP (0.2 GW/cm2) and lower than that of urea (1.50 GW/cm2) and MNC (0.9 GW/cm2) single crystals [4]. 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 neither hygroscopic nor soluble in water.
ARTICLE IN PRESS P.S. Patil, S.M. Dharmaprakash / Journal of Crystal Growth 305 (2007) 218–221
221
3.4. UV–vis–NIR absorption
Acknowledgments
Good transparency is also one of the important properties for a useful second-order nonlinear optical material. The UV–vis–NIR absorption spectra were recorded on a SHIMADZU 1601 UV spectrometer using an acetone solution and a quartz cell with a length of 10 mm. The cutoff wavelength is listed in Table 1. There was no absorption at the wavelength of SH (532 nm) (as shown in Fig. 3).
PSP thanks Defence Research Development Organization (DRDO), Government of India, for a Junior Research Fellowship (JRF). The authors are grateful to Professor M. Pattabi, Department of Materials Science, Mangalore University, Mangalagangotri, for providing the Powder XRD facility.
4. Conclusions 5-Br-2-thienyl-40 -methoxychalcone was synthesized and crystals were grown by slow-evaporation solution method at room temperature. Melting point of the crystal is moderately good. Lattice parameters have been calculated from PXRD studies. The relative SHG efficiency of the material is greater than that of urea. The UV–vis–NIR result elucidates that the crystal may find useful optical applications in the transparent wavelength window region 430–1100 nm. Furthermore, laser damage threshold was found to be 0.67 GW/cm2 for 1064 nm wavelength.
References [1] Y. Goto, A. Hayashi, Y. Kimura, M. Nakayama, J. Crystal Growth 108 (1991) 688. [2] G. Zhang, T. Kinoshita, K. Sasaki, Y. Goto, M. Nakayama, J. Crystal Growth 100 (1990) 411. [3] V. Shettigar, P.S. Patil, S. Naveen, S.M. Dharmaprakash, M.A. Sridhar, J. Shashidhara Prasad, J. Crystal Growth 245 (2006) 44. [4] P.S. Patil, S.M. Dharmaprakash, H.-K. Fun, M.S. Karthikeyan, J. Crystal Growth 297 (2006) 111. [5] P.S. Patil, S.M. Dharmaprakash, K. Ramakrishna, H.-K. Fun, R. Sai Santosh Kumar, D. Narayana Rao, J. Crystal Growth 303 (2007) 520. [6] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, vol. 1–2, Academic Press, New York, 1987. [7] J. Zyss, Molecular Nonlinear Optics, Academic Press, Boston, 1993. [8] J.N. Sherwood, Pure Appl. Opt. 7 (1998) 229. [9] P.S. Patil, S.-L. Ng, I.A. Razak, H.-K. Fun, S.M. Dharmaprakash, Acta Crystallogr. Sect. E 63 (2007) o59. [10] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798.