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A phase-matchable nonlinear optical material N-(3-nitrophenyl)phthalimide: Synthesis, crystal growth and characterization
ARTICLE IN PRESS
Journal of Crystal Growth 294 (2006) 318–322 www.elsevier.com/locate/jcrysgro
A phase-matchable nonlinear optical material N-(3-nitrophenyl)phthalimide: Synthesis, crystal growth and characterization H.J. Ravindra, M.R. Suresh Kumar, Chitharanjan Rai, S.M. Dharmaprakash Department of Physics, Mangalore University, Mangalagangotri 574199, Karnataka, India Received 8 March 2006; accepted 31 May 2006 Communicated by K.W.Benz Available online 26 July 2006
Abstract The N-(3-nitrophenyl)phthalimide (N3NP) single crystal of size 4 mm 1 mm 0.5 mm, sufficient enough to confirm the existence of phase-matching direction in the crystal using the Kurtz and Perry powder second-harmonic generation (SHG) measurements, was grown by slow evaporation solution growth technique using DMF solvent. Powder XRD, FTIR, CHN analysis and H1NMR technique were employed to characterize N3NP single crystal. The single crystal XRD data revealed the noncentrosymmetric crystal structure of N3NP, which is an essential criterion for SHG. The main contribution to the SHG results comes from the strong hydrogen bonds, which also appear as intense IR bands of hydrogen bond vibrations in spectral characteristics. From DT/TG analysis, the N3NP was found to be thermally stable up to 246 1C. The four C–H O hydrogen bonds, which hold the molecules of N3NP in three-dimensional crystal lattice, are responsible for the higher thermal stability. The UV–Vis optical absorption spectrum of N3NP shows the lower optical cut off at 370 nm and was transparent in the visible region. The N3NP is a phase-matchable NLO crystal. This crystal can be used as an efficient frequency doubler and optical parametric oscillator due to its high SHG conversion efficiency. r 2006 Elsevier B.V. All rights reserved. PACS: 81.10; 42.65 Keywords: A1. Characterization; A2. Crystal growth; B1. Organic material; B2. Nonlinear optical material
1. Introduction The rapid development in the field of optoelectronics greatly increased the demand for newer nonlinear optical (NLO) materials. In this regard, organic materials are of particular interest owing to their high nonlinearity, ultrafast response, high damage resistance, higher possibility to adopt theoretical modelling and flexibility to design new variety of molecules in this class of materials. For efficient second-harmonic generation (SHG), one requires highly polarizable molecular system (p-conjugated pathways) Corresponding author. Tel.: +91 0824 2287363; fax: +91 0824 2287367. E-mail address: [email protected] (S.M. Dharmaprakash).
0022-0248/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2006.05.084
having asymmetric charge distribution in the molecule (substituted donor and acceptor groups at the end of the molecule e.g., P-nitroaniline) with noncentrosymmetric crystal structure [1,2]. The m-disubstitued benzene derivatives are reported to have high tendency to crystallize in noncentrosymmetric crystal structure compared to ortho and para substitutions [3]. We have synthesized N-(3-nitrophenyl)phthalimide (N3NP) from m-disubstitued benzene compound m-nitro aniline (mNA). The N3NP crystallizes in monoclinic crystal system with noncentrosymmetric space group Pn and cell parameters a ¼ 6.6650(5) A˚, b ¼ 3.6962(3) A˚, c ¼ 23.639(2) A˚ and b ¼ 95.208(3)1 [4]. N3NP shows high thermal stability compared to standard organic NLO material urea and hippuric acid. The powder SHG conversion efficiency of
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N3NP was found to be 10 times that of reference urea. In this paper we report the synthesis, crystal growth and characterization of N3NP single crystal. 2. Experimental procedure 2.1. Synthesis and crystal growth The analytical reagent (AR) grade phthalic anhydride (PA) and mNA obtained from Spectrochemicals Company have been used without further purification for synthesizing N3NP. PA (0.1 mol) and mNA (0.1 mol) were dissolved in a required volume of glacial acetic acid. The whole solution was taken in a round-bottomed flask fitted with water-cooled condenser. The reaction mixture was refluxed for about 2 h. The solution was cooled and the precipitated N3NP was separated by filtration process. It was later purified by recrystallization process. The recorded melting point temperature of N3NP is 246 1C, which finds good agreement with that of literature (244–246 1C) [5,6]. The solution growth technique is widely employed to grow single crystals of organic compounds. In order to select the suitable solvent for crystal growth, the solubility of N3NP in different solvents such as acetone, methanol, ethanol, acetic acid and N,N-dimethylformamide (DMF) was measured. The solubility was determined by adding N3NP to known volume of solvent maintained at constant temperature till the dissolution ceased. Using this technique, we have determined the magnitude of solubility of N3NP for various temperatures ranging from 30 to 65 1C. The solubility of N3NP was found to be higher in DMF compared to other solvents. A plot of temperature versus solubility is shown in Fig. 1. From the solubility data DMF was found to be a better solvent for bulk single-crystal growth of N3NP. Synthesized N3NP is an off-white crystalline powder and was purified by repeated recrystallization process using DMF solvent. The purified sample was
Fig. 1. Solubility of N3NP in DMF solvent.
Fig. 2. Single crystals of N3NP.
used as raw material for single-crystal growth. A saturated solution of N3NP in DMF was prepared in a beaker at 32 1C. The temperature of the supersaturated solution was raised to 40 1C to get the homogeneous mixture. The solution was filtered and kept undisturbed in a beaker at 30 1C in a constant temperature water bath. Tiny crystals were formed in 3 d and the crystals reached a maximum size of 4 mm 1 mm 0.5 mm in a period of 8 d. The grown crystals were found to be elongated along crystallographic caxis due to higher growth rates compared to other two axes. The harvested crystals are shown in Fig. 2. N3NP crystals are transparent, nonhygroscopic and stable. 2.2. Characterization The grown N3NP crystals were characterized by powder X-ray diffraction (XRD), chemical analysis, thermal analysis and optical studies. The powder XRD pattern of N3NP was collected using BRUKER AXS D8 Advanced X-ray diffractometer with Cu Ka (l ¼ 1.5418 A˚) radiation in the 2y ranging from 10 to 501 at a scanning rate of 21 min1. Elemental analysis was carried out using Vario EL III CHNS analyzer. Fourier transform infrared (FTIR) spectrum was recorded in the spectral range 400–4000 cm1 using Shimadzu-8700 FTIR spectrometer, where the sample was in pallet form in KBr phase. Nuclear magnetic resonance (NMR) spectrum of N3NP was recorded using AMX-400 high-resolution multinuclear FT-NMR Spectrometer. The thermal analysis was carried out using Perkin Elmer simultaneous TG/DT analyzer and Mettler Toledo DSC822e differential scanning calorimeter (DSC) with a heating rate of 10 1C min1 under nitrogen atmosphere. The optical absorption spectrum was recorded using SECOMAM UV–Vis spectrophotometer in the wavelength range of 200–1000 nm using DATHELIE software. The NLO powder SHG efficiency was measured using the Kurtz and Perry technique.
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3. Results and discussion
Table 3 CHN analysis
3.1. XRD
Element
Powder XRD technique was used to identify the purity of the synthesized N3NP compound. The experimental and the calculated d values and also the h k l values are given in Table 1. The positions of the powder XRD peaks were found to be in good agreement with the calculated single crystal XRD data. The powder XRD pattern of N3NP was indexed and cell constants were calculated using PROSZKI software. The cell constants calculated from the powder XRD data are in good agreement with the single crystal data [4] and are presented in Table 2. Further, the density of the crystal was determined by flotation technique. The density of N3NP was found to be 1.530 g cm3, which is in good agreement with the density value 1.536 g cm3 obtained from XRD data.
3.2. Chemical analysis 3.2.1. Elemental analysis To know the percentage compositions of the elements present in the N3NP crystal elemental analysis were carried
Table 1 XRD data of N3NP crystal Peak position (2y)
dobs (A˚)
dcal (A˚)
I/Io
h
k
l
13.409 14.106 14.957 16.511 18.219 21.912 24.070 24.749 26.752 27.153 27.572 28.048 28.450 29.949 33.428 40.395 42.910
6.60305 6.27844 5.92283 5.36864 4.86903 4.05622 3.69718 3.59730 3.33228 3.28401 3.23505 3.18115 3.13709 2.98341 2.68045 2.23280 2.10759
6.63749 6.24214 5.88535 5.31101 4.85509 4.01612 3.69620 3.65147 3.32827 3.27274 3.22926 3.18045 3.13010 2.96170 2.69040 2.22452 2.10882
100 69 11 27 10 22 12 11 6 28 13 8 10 7 9 6 10
1 1 0 1 1 1 0 0 2 2 1 1 0 2 0 1 2
0 0 0 0 0 0 1 1 0 0 1 1 1 0 1 1 0
0 1 4 3 3 5 0 1 1 2 0 1 4 3 6 8 8
Table 2 Unit cell parameters of N3NP
a b c b V
Powder data
Single crystal data [4]
6.6650 A˚ 3.6932 A˚ 23.6558 A˚ 95.1531 579.9370 A˚3
6.6650 A˚ 3.6962 A˚ 23.6390 A˚ 95.2081 579.9500 A˚3
Carbon Hydrogen Nitrogen
Composition (%) Theoretical
Experimental
62.686 2.985 10.447
62.609 2.764 10.442
out. About 5 mg of the sample was used for elemental analysis. Table 3 shows the experimental and theoretical percentage compositions of elements present in N3NP. The experimentally determined percentage compositions of the elements are in good agreement with that of the theoretical calculation. 3.2.2. FTIR spectral analysis The FTIR spectrum of N3NP is shown in Fig. 3. The characteristic absorption bands were observed in spectral range 500–1800 cm1. In the N3NP molecular-packing diagram proposed by Glidewell [4], there is a formation of hydrogen bond between CH of the aromatic ring and O of the carbonyl group and CH and O of NO2 group. In the FTIR spectrum the peak due to aromatic C–H stretching appears as a weak absorption band at 3099.4 cm1 and hence the hydrogen-bonding interactions could be strong. The sharp absorption band at 1726.2 cm1 is assigned to CQO stretching vibration (imide) and the medium absorption bands at 1529.4 and 1350.1 cm1 are attributed to NQO (aromatic NO2) asymmetric stretching and NQO (aromatic NO2) symmetric-stretching vibrations, respectively which indicate the carbonyl oxygen atoms are more active as hydrogen bond acceptors than the nitrooxygen atom. The bands assigned to C–C stretching vibrations are weaker and appear in the broader region of 1200–800 cm1. The absorption band at 707.8 cm1 was assigned to the out of plane QC–H bending in the FTIR spectrum. 3.2.3. NMR spectral analysis NMR spectrum of N3NP was recorded using AMX-400 high resolution multinuclear FT-NMR Spectrometer. The 1 H NMR spectrum of N3NP is shown in Fig. 4. The peaks observed at dH 2.50 and 3.31 are due to the presence of unduteriated DMSO in the solvent and the methanol moisture, respectively. The remaining peaks in the NMR spectrum are characteristics of the N3NP compound. The triplet observed at dH 7.85 is due to single aryl proton. The multiplet observed in the dH range 7.91–8.07 and 8.28–8.35 are due to coupled integration of 5H aryl protons and integration of single aryl proton, respectively. The triplet observed at 8.35 is due to single aryl proton. All the peaks observed are in good agreement with the literature [5], confirming the molecular structure of N3NP.
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Fig. 3. FTIR spectrum of N3NP crystal.
Fig. 5. TG/DTA curve of N3NP crystal.
Fig. 4. NMR spectrum of N3NP crystal.
3.3. DT/TG analysis The TG/DT curves for N3NP crystal are shown in Fig. 5. N3NP crystal exhibits single sharp weight loss at 246 1C. Below this temperature no weight loss is observed in the TGA curve. The endothermic peak observed at 246 1C in the DTA curve is due to melting of the compound, which is accompanied by weight loss. Below this endothermic peak there is no exothermic or endothermic peak, indicating the absence of any isomorphic transition. Above the weight loss temperature endotherm no characteristic exothermic or endothermic peaks are observed, hence there should be volatilization of N3NP without any degradation. Hence N3NP is thermally stable up to 246 1C. Thermal stability of N3NP crystal was further confirmed using DSC results (Fig. 6). N3NP crystal has high melting point compared to the melting point temperature of standard organic NLO materials viz: urea (130 1C), mNA (114 1C) p-hydroxyacetophenone (110 1C) and hippuric acid (189 1C).
Fig. 6. DSC curve of N3NP crystal.
3.4. UV–Vis spectra Absorption spectra of NLO material play a major role in device fabrication. Wider the transparency window more will be the practical applicability of that material. To know
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Fig. 7. UV–Vis spectra of N3NP crystal. Fig. 8. Particle size dependence of the SHG output of N3NP.
the transparency range of N3NP, optical absorption spectra was recorded in the wavelength range of 200–1000 nm and is shown in Fig. 7. The lower optical cutoff is observed at 370 nm. The absorption is negligible in the entire visible region of electromagnetic spectrum. Therefore N3NP can be used as a potential material for SHG in the visible region. 3.5. SHG The powder SHG efficiency of N3NP crystal was determined using Kurtz and Perry powder SHG technique [7] using the Q-switched Nd: YAG (Quanta Ray Spectra Physics model Prolab170) laser operating at 1064 nm, pulse width 8 ns; pulse repetition rate 10 Hz and energy 2.9 mJ/ pulse. The particle size of N3NP and the reference urea crystal was between 125–250 mm. The powder SHG efficiency of N3NP was found to be 10 times that of urea. The main contribution to higher SHG conversion efficiency in N3NP results from the hydrogen bonds and also from the vibrational part due to very-intense IR bands of the hydrogen bond vibrations [8,9]. To confirm the existence of phase-matching direction in the N3NP crystal, the particle size dependency of SHG intensity was studied. Particles of size ranging from o63, 63–125, 125–250 and 250–355 mm were obtained using standard sieves of 63, 125, 250 and 355 mm. The SHG intensity increases with the increase in particle size from o63 to 125–250 mm. Above this range (125–250 mm) the SHG intensity becomes independent of particle size (Fig. 8). This kind of particle size dependency on SHG intensity exits only in phase-matchable materials. Hence N3NP crystal can be used as an efficient frequency doubler and optical parametric oscillator provided large-size single crystals are available.
4. Conclusion The single crystals of N3NP were grown by slow evaporation solution growth technique. The grain size dependency of SHG intensity shows that a phase-matching direction exists in this crystal. The N3NP crystal has high thermal stability and it shows good optical transparency in the entire visible region of electromagnetic spectrum. The results of the present experiment show that the SHG conversion efficiency of N3NP crystal is 10 times that of the reference urea. Acknowledgments Authors thank Prof. P.K. DAS, IPC, IISC Bangalore for having extended the laser facility, the Coordinator, DSTXRD project, Mangalore University for providing XRD facility, Microtron Center, Mangalore University for providing UV–Vis spectrometer facility, Dr. Boja Poojaari, Department of Chemistry for providing FTIR facility and Mr. Vinay Shetty for his help. References [1] D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic Molecules and Crystals, vols. 1 and 2, Academic press, New York, 1997. [2] R.W. Munn, C.N. Ironside (Eds.), Principles and Applications of Nonlinear Optical Materials, Chapman & Hall, London, 1993. [3] D.Y. Curtin, I.C. Paul, Chem. Rev. 81 (1981) 525. [4] C. Glidewell, J.N. Low, J.M.S. Skakle, J.L. Wardell, Acta. Crystallogr. C 60 (2004) o24. [5] C.J. Perry, Z. Parveen, J. Chem. Soc. Perkins Trans. 2 (2001) 512. [6] R.G.R. Bacon, A. Karim, J. Chem. Soc. Perkins Trans. 1 (1973) 273. [7] S.K. Kurtz, T.T. Perry, J. Appl. Phys 39 (1968) 3798. [8] M.R. Suresh Kumar, H.J. Ravindra, A. Jayarama, S.M. Dharmaprakash, J. Crystal Growth 286 (2006) 451. [9] B. Narayana Moolya, A. Jayarama, M.R. Suresh Kumar, S.M. Dharmaprakash, J. Crystal Growth 280 (2006) 581.
Journal of Crystal Growth 294 (2006) 318–322 www.elsevier.com/locate/jcrysgro
A phase-matchable nonlinear optical material N-(3-nitrophenyl)phthalimide: Synthesis, crystal growth and characterization H.J. Ravindra, M.R. Suresh Kumar, Chitharanjan Rai, S.M. Dharmaprakash Department of Physics, Mangalore University, Mangalagangotri 574199, Karnataka, India Received 8 March 2006; accepted 31 May 2006 Communicated by K.W.Benz Available online 26 July 2006
Abstract The N-(3-nitrophenyl)phthalimide (N3NP) single crystal of size 4 mm 1 mm 0.5 mm, sufficient enough to confirm the existence of phase-matching direction in the crystal using the Kurtz and Perry powder second-harmonic generation (SHG) measurements, was grown by slow evaporation solution growth technique using DMF solvent. Powder XRD, FTIR, CHN analysis and H1NMR technique were employed to characterize N3NP single crystal. The single crystal XRD data revealed the noncentrosymmetric crystal structure of N3NP, which is an essential criterion for SHG. The main contribution to the SHG results comes from the strong hydrogen bonds, which also appear as intense IR bands of hydrogen bond vibrations in spectral characteristics. From DT/TG analysis, the N3NP was found to be thermally stable up to 246 1C. The four C–H O hydrogen bonds, which hold the molecules of N3NP in three-dimensional crystal lattice, are responsible for the higher thermal stability. The UV–Vis optical absorption spectrum of N3NP shows the lower optical cut off at 370 nm and was transparent in the visible region. The N3NP is a phase-matchable NLO crystal. This crystal can be used as an efficient frequency doubler and optical parametric oscillator due to its high SHG conversion efficiency. r 2006 Elsevier B.V. All rights reserved. PACS: 81.10; 42.65 Keywords: A1. Characterization; A2. Crystal growth; B1. Organic material; B2. Nonlinear optical material
1. Introduction The rapid development in the field of optoelectronics greatly increased the demand for newer nonlinear optical (NLO) materials. In this regard, organic materials are of particular interest owing to their high nonlinearity, ultrafast response, high damage resistance, higher possibility to adopt theoretical modelling and flexibility to design new variety of molecules in this class of materials. For efficient second-harmonic generation (SHG), one requires highly polarizable molecular system (p-conjugated pathways) Corresponding author. Tel.: +91 0824 2287363; fax: +91 0824 2287367. E-mail address: [email protected] (S.M. Dharmaprakash).
0022-0248/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2006.05.084
having asymmetric charge distribution in the molecule (substituted donor and acceptor groups at the end of the molecule e.g., P-nitroaniline) with noncentrosymmetric crystal structure [1,2]. The m-disubstitued benzene derivatives are reported to have high tendency to crystallize in noncentrosymmetric crystal structure compared to ortho and para substitutions [3]. We have synthesized N-(3-nitrophenyl)phthalimide (N3NP) from m-disubstitued benzene compound m-nitro aniline (mNA). The N3NP crystallizes in monoclinic crystal system with noncentrosymmetric space group Pn and cell parameters a ¼ 6.6650(5) A˚, b ¼ 3.6962(3) A˚, c ¼ 23.639(2) A˚ and b ¼ 95.208(3)1 [4]. N3NP shows high thermal stability compared to standard organic NLO material urea and hippuric acid. The powder SHG conversion efficiency of
ARTICLE IN PRESS H.J. Ravindra et al. / Journal of Crystal Growth 294 (2006) 318–322
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N3NP was found to be 10 times that of reference urea. In this paper we report the synthesis, crystal growth and characterization of N3NP single crystal. 2. Experimental procedure 2.1. Synthesis and crystal growth The analytical reagent (AR) grade phthalic anhydride (PA) and mNA obtained from Spectrochemicals Company have been used without further purification for synthesizing N3NP. PA (0.1 mol) and mNA (0.1 mol) were dissolved in a required volume of glacial acetic acid. The whole solution was taken in a round-bottomed flask fitted with water-cooled condenser. The reaction mixture was refluxed for about 2 h. The solution was cooled and the precipitated N3NP was separated by filtration process. It was later purified by recrystallization process. The recorded melting point temperature of N3NP is 246 1C, which finds good agreement with that of literature (244–246 1C) [5,6]. The solution growth technique is widely employed to grow single crystals of organic compounds. In order to select the suitable solvent for crystal growth, the solubility of N3NP in different solvents such as acetone, methanol, ethanol, acetic acid and N,N-dimethylformamide (DMF) was measured. The solubility was determined by adding N3NP to known volume of solvent maintained at constant temperature till the dissolution ceased. Using this technique, we have determined the magnitude of solubility of N3NP for various temperatures ranging from 30 to 65 1C. The solubility of N3NP was found to be higher in DMF compared to other solvents. A plot of temperature versus solubility is shown in Fig. 1. From the solubility data DMF was found to be a better solvent for bulk single-crystal growth of N3NP. Synthesized N3NP is an off-white crystalline powder and was purified by repeated recrystallization process using DMF solvent. The purified sample was
Fig. 1. Solubility of N3NP in DMF solvent.
Fig. 2. Single crystals of N3NP.
used as raw material for single-crystal growth. A saturated solution of N3NP in DMF was prepared in a beaker at 32 1C. The temperature of the supersaturated solution was raised to 40 1C to get the homogeneous mixture. The solution was filtered and kept undisturbed in a beaker at 30 1C in a constant temperature water bath. Tiny crystals were formed in 3 d and the crystals reached a maximum size of 4 mm 1 mm 0.5 mm in a period of 8 d. The grown crystals were found to be elongated along crystallographic caxis due to higher growth rates compared to other two axes. The harvested crystals are shown in Fig. 2. N3NP crystals are transparent, nonhygroscopic and stable. 2.2. Characterization The grown N3NP crystals were characterized by powder X-ray diffraction (XRD), chemical analysis, thermal analysis and optical studies. The powder XRD pattern of N3NP was collected using BRUKER AXS D8 Advanced X-ray diffractometer with Cu Ka (l ¼ 1.5418 A˚) radiation in the 2y ranging from 10 to 501 at a scanning rate of 21 min1. Elemental analysis was carried out using Vario EL III CHNS analyzer. Fourier transform infrared (FTIR) spectrum was recorded in the spectral range 400–4000 cm1 using Shimadzu-8700 FTIR spectrometer, where the sample was in pallet form in KBr phase. Nuclear magnetic resonance (NMR) spectrum of N3NP was recorded using AMX-400 high-resolution multinuclear FT-NMR Spectrometer. The thermal analysis was carried out using Perkin Elmer simultaneous TG/DT analyzer and Mettler Toledo DSC822e differential scanning calorimeter (DSC) with a heating rate of 10 1C min1 under nitrogen atmosphere. The optical absorption spectrum was recorded using SECOMAM UV–Vis spectrophotometer in the wavelength range of 200–1000 nm using DATHELIE software. The NLO powder SHG efficiency was measured using the Kurtz and Perry technique.
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3. Results and discussion
Table 3 CHN analysis
3.1. XRD
Element
Powder XRD technique was used to identify the purity of the synthesized N3NP compound. The experimental and the calculated d values and also the h k l values are given in Table 1. The positions of the powder XRD peaks were found to be in good agreement with the calculated single crystal XRD data. The powder XRD pattern of N3NP was indexed and cell constants were calculated using PROSZKI software. The cell constants calculated from the powder XRD data are in good agreement with the single crystal data [4] and are presented in Table 2. Further, the density of the crystal was determined by flotation technique. The density of N3NP was found to be 1.530 g cm3, which is in good agreement with the density value 1.536 g cm3 obtained from XRD data.
3.2. Chemical analysis 3.2.1. Elemental analysis To know the percentage compositions of the elements present in the N3NP crystal elemental analysis were carried
Table 1 XRD data of N3NP crystal Peak position (2y)
dobs (A˚)
dcal (A˚)
I/Io
h
k
l
13.409 14.106 14.957 16.511 18.219 21.912 24.070 24.749 26.752 27.153 27.572 28.048 28.450 29.949 33.428 40.395 42.910
6.60305 6.27844 5.92283 5.36864 4.86903 4.05622 3.69718 3.59730 3.33228 3.28401 3.23505 3.18115 3.13709 2.98341 2.68045 2.23280 2.10759
6.63749 6.24214 5.88535 5.31101 4.85509 4.01612 3.69620 3.65147 3.32827 3.27274 3.22926 3.18045 3.13010 2.96170 2.69040 2.22452 2.10882
100 69 11 27 10 22 12 11 6 28 13 8 10 7 9 6 10
1 1 0 1 1 1 0 0 2 2 1 1 0 2 0 1 2
0 0 0 0 0 0 1 1 0 0 1 1 1 0 1 1 0
0 1 4 3 3 5 0 1 1 2 0 1 4 3 6 8 8
Table 2 Unit cell parameters of N3NP
a b c b V
Powder data
Single crystal data [4]
6.6650 A˚ 3.6932 A˚ 23.6558 A˚ 95.1531 579.9370 A˚3
6.6650 A˚ 3.6962 A˚ 23.6390 A˚ 95.2081 579.9500 A˚3
Carbon Hydrogen Nitrogen
Composition (%) Theoretical
Experimental
62.686 2.985 10.447
62.609 2.764 10.442
out. About 5 mg of the sample was used for elemental analysis. Table 3 shows the experimental and theoretical percentage compositions of elements present in N3NP. The experimentally determined percentage compositions of the elements are in good agreement with that of the theoretical calculation. 3.2.2. FTIR spectral analysis The FTIR spectrum of N3NP is shown in Fig. 3. The characteristic absorption bands were observed in spectral range 500–1800 cm1. In the N3NP molecular-packing diagram proposed by Glidewell [4], there is a formation of hydrogen bond between CH of the aromatic ring and O of the carbonyl group and CH and O of NO2 group. In the FTIR spectrum the peak due to aromatic C–H stretching appears as a weak absorption band at 3099.4 cm1 and hence the hydrogen-bonding interactions could be strong. The sharp absorption band at 1726.2 cm1 is assigned to CQO stretching vibration (imide) and the medium absorption bands at 1529.4 and 1350.1 cm1 are attributed to NQO (aromatic NO2) asymmetric stretching and NQO (aromatic NO2) symmetric-stretching vibrations, respectively which indicate the carbonyl oxygen atoms are more active as hydrogen bond acceptors than the nitrooxygen atom. The bands assigned to C–C stretching vibrations are weaker and appear in the broader region of 1200–800 cm1. The absorption band at 707.8 cm1 was assigned to the out of plane QC–H bending in the FTIR spectrum. 3.2.3. NMR spectral analysis NMR spectrum of N3NP was recorded using AMX-400 high resolution multinuclear FT-NMR Spectrometer. The 1 H NMR spectrum of N3NP is shown in Fig. 4. The peaks observed at dH 2.50 and 3.31 are due to the presence of unduteriated DMSO in the solvent and the methanol moisture, respectively. The remaining peaks in the NMR spectrum are characteristics of the N3NP compound. The triplet observed at dH 7.85 is due to single aryl proton. The multiplet observed in the dH range 7.91–8.07 and 8.28–8.35 are due to coupled integration of 5H aryl protons and integration of single aryl proton, respectively. The triplet observed at 8.35 is due to single aryl proton. All the peaks observed are in good agreement with the literature [5], confirming the molecular structure of N3NP.
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Fig. 3. FTIR spectrum of N3NP crystal.
Fig. 5. TG/DTA curve of N3NP crystal.
Fig. 4. NMR spectrum of N3NP crystal.
3.3. DT/TG analysis The TG/DT curves for N3NP crystal are shown in Fig. 5. N3NP crystal exhibits single sharp weight loss at 246 1C. Below this temperature no weight loss is observed in the TGA curve. The endothermic peak observed at 246 1C in the DTA curve is due to melting of the compound, which is accompanied by weight loss. Below this endothermic peak there is no exothermic or endothermic peak, indicating the absence of any isomorphic transition. Above the weight loss temperature endotherm no characteristic exothermic or endothermic peaks are observed, hence there should be volatilization of N3NP without any degradation. Hence N3NP is thermally stable up to 246 1C. Thermal stability of N3NP crystal was further confirmed using DSC results (Fig. 6). N3NP crystal has high melting point compared to the melting point temperature of standard organic NLO materials viz: urea (130 1C), mNA (114 1C) p-hydroxyacetophenone (110 1C) and hippuric acid (189 1C).
Fig. 6. DSC curve of N3NP crystal.
3.4. UV–Vis spectra Absorption spectra of NLO material play a major role in device fabrication. Wider the transparency window more will be the practical applicability of that material. To know
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Fig. 7. UV–Vis spectra of N3NP crystal. Fig. 8. Particle size dependence of the SHG output of N3NP.
the transparency range of N3NP, optical absorption spectra was recorded in the wavelength range of 200–1000 nm and is shown in Fig. 7. The lower optical cutoff is observed at 370 nm. The absorption is negligible in the entire visible region of electromagnetic spectrum. Therefore N3NP can be used as a potential material for SHG in the visible region. 3.5. SHG The powder SHG efficiency of N3NP crystal was determined using Kurtz and Perry powder SHG technique [7] using the Q-switched Nd: YAG (Quanta Ray Spectra Physics model Prolab170) laser operating at 1064 nm, pulse width 8 ns; pulse repetition rate 10 Hz and energy 2.9 mJ/ pulse. The particle size of N3NP and the reference urea crystal was between 125–250 mm. The powder SHG efficiency of N3NP was found to be 10 times that of urea. The main contribution to higher SHG conversion efficiency in N3NP results from the hydrogen bonds and also from the vibrational part due to very-intense IR bands of the hydrogen bond vibrations [8,9]. To confirm the existence of phase-matching direction in the N3NP crystal, the particle size dependency of SHG intensity was studied. Particles of size ranging from o63, 63–125, 125–250 and 250–355 mm were obtained using standard sieves of 63, 125, 250 and 355 mm. The SHG intensity increases with the increase in particle size from o63 to 125–250 mm. Above this range (125–250 mm) the SHG intensity becomes independent of particle size (Fig. 8). This kind of particle size dependency on SHG intensity exits only in phase-matchable materials. Hence N3NP crystal can be used as an efficient frequency doubler and optical parametric oscillator provided large-size single crystals are available.
4. Conclusion The single crystals of N3NP were grown by slow evaporation solution growth technique. The grain size dependency of SHG intensity shows that a phase-matching direction exists in this crystal. The N3NP crystal has high thermal stability and it shows good optical transparency in the entire visible region of electromagnetic spectrum. The results of the present experiment show that the SHG conversion efficiency of N3NP crystal is 10 times that of the reference urea. Acknowledgments Authors thank Prof. P.K. DAS, IPC, IISC Bangalore for having extended the laser facility, the Coordinator, DSTXRD project, Mangalore University for providing XRD facility, Microtron Center, Mangalore University for providing UV–Vis spectrometer facility, Dr. Boja Poojaari, Department of Chemistry for providing FTIR facility and Mr. Vinay Shetty for his help. References [1] D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic Molecules and Crystals, vols. 1 and 2, Academic press, New York, 1997. [2] R.W. Munn, C.N. Ironside (Eds.), Principles and Applications of Nonlinear Optical Materials, Chapman & Hall, London, 1993. [3] D.Y. Curtin, I.C. Paul, Chem. Rev. 81 (1981) 525. [4] C. Glidewell, J.N. Low, J.M.S. Skakle, J.L. Wardell, Acta. Crystallogr. C 60 (2004) o24. [5] C.J. Perry, Z. Parveen, J. Chem. Soc. Perkins Trans. 2 (2001) 512. [6] R.G.R. Bacon, A. Karim, J. Chem. Soc. Perkins Trans. 1 (1973) 273. [7] S.K. Kurtz, T.T. Perry, J. Appl. Phys 39 (1968) 3798. [8] M.R. Suresh Kumar, H.J. Ravindra, A. Jayarama, S.M. Dharmaprakash, J. Crystal Growth 286 (2006) 451. [9] B. Narayana Moolya, A. Jayarama, M.R. Suresh Kumar, S.M. Dharmaprakash, J. Crystal Growth 280 (2006) 581.