Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 324–328
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Short Communication
Crystal growth and characterization of an organic nonlinear optical single crystal: 2,3-Dimethyl-N-[4-(Nitro) benzylidene] aniline R.K. Balachandar, S. Kalainathan ⇑ Centre for Crystal Growth, SAS, VIT University, Vellore 632 014, Tamil Nadu, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Single crystals of DNBA were grown
by slow evaporation growth technique. The blue emission of the crystal was identified by Photoluminescence spectral analysis. Thermally stable up to 141 °C. SHG efficiency 4.08 times higher than KDP.
a r t i c l e
i n f o
Article history: Received 18 October 2013 Received in revised form 27 January 2014 Accepted 19 February 2014 Available online 12 March 2014 Keywords: Organic compounds Crystal growth Optical properties X-ray diffraction Second harmonic generation
a b s t r a c t An organic nonlinear optical material 2,3-Dimethyl-N-[4-(Nitro) benzylidene] aniline was synthesized by condensation reaction. The single crystals were grown by the slow evaporation technique at room temperature using ethyl acetate as solvent with large in size and having transparent nature. The unit cell parameters were determined and belong to a noncentrosymmetric orthorhombic crystal structure by single crystal X-ray diffraction. The crystalline nature of the synthesized material was recorded by the powder X-ray diffraction pattern. The molecular structure of the grown material was investigated by proton and carbon nuclear magnetic resonance, mass spectrum analysis. Functional groups were identified by the vibration spectrum analysis. The optical absorbance of the grown crystal was ascertained by Ultraviolet–Visible spectrum. Thermal behaviour and stability of the grown material was investigated by thermo gravimetric/differential thermal analysis. The nonlinear optic conversion efficiency was determined by powder technique and found to be 4.08 times greater that of KDP as a standard reference. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Schiff base is an essential class of organic materials that shows considerable crystallizability has been studying various properties such as biological activity and anti-HIV effect [1,2]. The versatile properties of the Schiff base compound have received an excellent deal of attention in the recent years, also studied extensively which ⇑ Corresponding author. Tel.: +91 416 2202350; fax: +91 416 2243092. E-mail address: [email protected] (S. Kalainathan). http://dx.doi.org/10.1016/j.saa.2014.02.084 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
exhibit strong nonlinear optical properties [3,4]. In the recent years, we have reported the crystal structure and crystal growth of some organic nonlinear optical (NLO) materials. Organic materials with highly nonlinear optical susceptibilities are considered to be potential alternatives to the inorganic materials for applications in Photonics and optoelectronics [5–7]. As a result, there is an increasing interest in designing and crystallizing new organic materials with desired linear and nonlinear optical properties. In this work, we report the synthesis of 2,3-Dimethyl-N-[4-(Nitro) benzylidene] aniline (DNBA) a Schiff base compound and single
R.K. Balachandar, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 324–328
crystals were grown in centimetre size. The confirmation of structural and functional group of the title material was characterized by spectroscopic technique. Also, we studied optical, thermal and the second harmonic generation (SHG) behaviour of the materials by powder SHG technique.
325
powder XRD pattern of title crystal (h, k, l) values were indexed using powder X software program and is shown in Fig. 1. 1
H and
13
C NMR spectral analysis
1
Experimental Material synthesis and crystal growth of DNBA An equimolar ratio of 2,3-dimethylaniline (1.22 ml) and 4-Nitrobenzaldehyde (1.51 g) each of 10 mmol were taken in a round bottom flask, refluxed in methanol for 30 min resulting in yellow colour solid precipitates due to the condensation reaction between the two molecules with water as by product. Then filtering the precipitates with filter paper and the crude material were dried at room temperature. The crude material was recrystallized with methanol in order to become purified synthesized material. Fig. S1 in supplementary shows the reaction scheme of the DNBA. The recrystallized material was dissolved in the solvent as ethyl acetate and stirred continuously for 6 h using a magnetic stirrer, and the saturated solution was prepared, filtered and covered tightly with aluminium foil kept undisturbed at room temperature for controlling slow evaporation of the solvent. Natural slow evaporation of the ethyl acetate induces the spontaneous nucleation in the solution, and tiny seed single crystals of optically transparent observe in nature have been occurring after 5 days and resulted larger size single crystal harvested after 10 days. Fig. S2 in supplementary shows the grown DNBA single crystal. Results and discussion Single crystal X-ray diffraction Single crystal XRD study was performed to determine the unit cell parameter of the grown single crystal by using diffractometer-Bruker Kappa Apex II. The single crystal XRD study reveals that the DNBA belongs to non-centrosymmetric orthorhombic system with the space group ‘‘P212121’’, the lattice parameter a = 7.168 Å, b = 11.844 Å, c = 15.374 Å and V = 1305.2 Å, satisfying one of the basic and foremost requirements for the SHG activity of the single crystal material, the obtained unit cell parameter values were in close agreement with those of reported values [8,9]. Table 1 shows the unit cell parameter of the reported and current work of the DNBA.
H and 13C NMR spectrum of the purified DNBA sample were recorded using Bruker 400 MHz instrument in deuterated chloroform (CDCl3) with tetramethylsilane (TMS) as the internal standard. The structure of DNBA containing different types of protons shows distinct peaks as expected at different chemical shift positions from the different environment of the proton. The imine protons (AHC@NA) act as a singlet. The singlet signal at d = 8.436 ppm corresponds to the proton of imine group, which confirms the formation of the Schiff base compound [10,11]. The protons of two methyl (CH3) group attached to the aromatic radicals are observed two separate singlets at d = 2.313 and d = 2.326 ppm respectively. The aromatic shifts of different protons were observed in the various environments, in the region from d = 6.812 to 8.315 ppm which contains two doublet and one triplet. 1 H NMR spectrum of the grown material is shown in supplementary Fig. S3. From 13C NMR of the title compound, the assignment of the each signal is a distinctive carbon environment in the molecule is also identified. The shift (d = 156.42 ppm) is due to the imine group carbon atom which confirms the creation of the Schiff base compound. The signal at d = 149.20 and 149.99 ppm refer to the Nitro group attached to the aromatic carbon atom and the nitrogen (ACH@NAAr) attached to the aromatic ring and from the imine linkage carbon atom. The peaks correspond to the aromatic carbon, which appear on the aromatic parts from (d = 115.13 to 141.97 ppm). The signal (d = 13.97 ppm and d = 20.21 ppm) were expected to the two methyl group carbon atom attached to the aromatic ring and the three-line signal (d = 76.85, 77.16, 77.48 ppm) from the CDCl3 solvent corresponds to the single carbon atom; it appears as a triplet because of an interaction with the deuterium atom. Thus, the molecular structure of the title compound is confirmed from the proton and carbon NMR spectrum. 13C NMR spectrum of title material is shown in supplementary Fig. S4. FTIR and FT-Raman spectral analysis To analysis qualitatively the presence of the functional group in the grown crystal, Fourier Transforms Infrared spectrum (FTIR) was recorded in the solid state as KBr discs technique using a
Powder X-ray diffraction The Fine crushed powder of DNBA single crystal was scanned in the 2h values ranging from 10° to 60°, and the powder X-ray diffraction pattern was recorded with Bruker, D8 Advance model, Cu Ka radiation (k = 1.5406 (Å)). The prominent peaks in the
Table 1 Unit cell parameter of reported and present work of DNBA. Parameters
Reported [6]
Present work
Crystal system Space group a b c V Molecular formula Molecular weight
Orthorhombic P212121 7.1969 (5) Å 11.8023 (7) Å 15.3721 (14) Å 1305.71(14) Å3 C15H15NO 225.2857
Orthorhombic P212121 7.168 ± 0.005 Å 11.844 ± 0.009 Å 15.374 ± 0.009 Å 1305.2 ± 0.4 Å3
Fig. 1. Powder XRD pattern of DNBA.
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HR-Mass spectral analysis A high resolution mass spectrum is shown in supplementary Fig. S5 helps to determine the exact mass of the molecular ion of the compound [14]. The parent molecular ion is often the largest mass which is not fragmented. The calculated molecular weight is 254.2838, and from the mass spectrum, it is observed that the parent ion peak representing the correct mass of the DNBA is to be at 254.2800 (m/z). The mass spectrum also shows other peaks corresponding to fragment ions resulting from the breaking of certain bonds as follows, the peak at 222.2088 (m/z) are due the fragmentation of the Nitro group on the aromatic ring. The peak at 181.3162 (m/z) is due the fragmentation of two methyl and Nitro group group attached to the aromatic ring and the peak at 151.3259 (m/z) is expected to the complete cleavage of the 2,3dimethylaniline from the aldehyde compound. UV–Visible spectral analysis
Fig. 2. FTIR spectrum of the DNBA.
Shimadzu FTIR spectrophotometer in the range of 400–4000 cm 1. Fourier Transform-Raman was recorded in the Bruker RFS, in the range from 50 to 5000 cm 1. The recorded FTIR and F-Raman spectra shown in Figs. 2 and 3. The absorption band assignment to the stretching of C@N bond was observed at frequency 1622 cm 1, and this value confirms with the reported in the FTIR spectrum of Schiff base in the case of FT-Raman it is observed at 1623 cm 1 [12,13]. The aromatic hydrogen absorption band is observed at 3081 and 2978 cm 1 (m CH asymmetry aromatic and m CH symmetry aromatic). In the FT-Raman, it was observed at 3078 and 2913 cm 1. CAC stretching absorptions are absorptions expected around 1597–1512 cm 1 in the FTIR. In the case of FT-Raman observed in 1595–1512 cm 1. With the help of FTIR and FT-Raman spectrum, the presence of the specific functional groups of the title material is confirmed.
The optical absorption spectrum of the grown crystal was recorded using Elico SL218 Double beam UV–Visible spectrophotometer in the wavelength range of 190–1100 nm at room temperature. A sample of 2.33 mm thickness of as grown crystal was used for measurement without polishing the crystal surface. The recorded Ultraviolet–Visible (UV–Visible) absorbance spectrum is shown in Fig. 4. It is observed that the maximum absorbance at 380 nm in the UV region and the cutoff wavelength is 450 nm. The crystal has low absorption starts in the visible and downright reaches a minimum in the NIR region. The high excited-to-ground state dipole moment, which increases the optical nonlinearity also increases the absorption in the UV–Visible spectrum [15]. Also, there is a little absorbance at the frequency doubling wavelength (532 nm), which improves the SHG output. Photoluminescence study The Photoluminescence emission was found by exciting the crystalline powder of the grown material using light of wavelength where maximum absorption was obtained. The PL spectra were recorded using a Jobin Yvon–Spex Spectro-fluorometer (Fluorolog version-3; Model FL3-11) at room temperature. The excitation source used was a Xenon arc lamp (450 W). The detector (PMTR928P) has a flat response from 200 to 900 nm and the spectral
Fig. 3. FT-Raman spectrum of the grown material.
R.K. Balachandar, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 324–328
327
Fig. 6. TG/DTA thermal analysis of the DNBA. Fig. 4. UV–Visible spectrum of the grown material.
resolution of 0.2 nm. The sample is excited at the wavelength of 450 nm chosen from UV–Visible studies. The recorded PL spectrum is shown in Fig. 5. The band gap energy of the material from the highest peak intensity was calculated from the formula Eg = hc/ke. Here, h, c and e are universal constants and the k is the wavelength of the maximum intensity. The calculated band gap energy is about Eg = 2.567 eV and Eg = 2.52 eV (at two emission peak 483 nm and 493 nm). From the PL spectrum, it is concluded that it shows two peaks with a peak wavelength at 483 nm and 492 nm which emits blue emission [16]. Thermal analysis The thermal stability of the grown crystal was measured by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) simultaneously using Netzsch STA 409 PL Luxx. Fig. 6 shows the TG/DTA thermal analysis of the grown material. A powder
sample of weighing about 11.662 mg was taken in an alumina crucible was used for heating the sample. The study was carried out in the nitrogen atmosphere at the heating rate of 10 K/min over from the room temperature to 500 °C. From DTA thermogram that an endothermic event begins at 136 °C and the sharpness of peak appears at 141 °C which is due to the melting point of the sample. The sharpness of the endothermic peak indicates that considerable crystalline nature and purity of the material were clearly observed from thermal analysis. Solid–liquid phase transition observed in the during the melting point, and up to 225 °C before the decomposition of the material and there is no other transition noticed. From TG curve, it is observed that the material does not sublime and is stable up to 225 °C. A peak at 353 °C shows the entire decomposition of the grown material. About 6.33% of carbon residues were present. From the thermal analysis, it is concluded that the material is quite stable up to 141 °C, and it could be expected utility of any suitable applications up to this temperature. Powder SHG measurement
Fig. 5. PL spectrum of the DNBA.
The grown crystals were characterized one of the optical studies by second harmonic generation efficiency. NLO efficiency was carried out by Kurtz and Perry powder technique to determine the materials with non-centrosymmetric crystal structure. Both DNBA and KDP crystal were powdered to uniform particle size in order to make relative comparisons with known KDP SHG materials [17]. The crystalline powder sample was filled airtight with microcapillary tubes of uniform bore of about 1.5 mm in diameter. A high intensity pulsed Nd:YAG laser of wavelength 1064 nm with input beam energy 3.8 mJ/pulse and pulse width 10 ns with a repetition rate of 10 Hz were used. The crystalline powdered samples with a uniform particle in the micro-Capillary tube were exposed to the laser radiation. The second harmonic signal was generated from crystalline powder sample was confirmed by the bright green light emission (k = 532 nm) was observed which indicates the SHG behaviour of the DNBA material, was detected by a photomultiplier tube (PMT) and viewed on the oscilloscope (CRO). The optical signal fed into the PMT was converted into voltage output at the CRO. The value obtained in the CRO was compared with the voltage output for a standard KDP sample. The ratio of the two values gives the relative SHG efficiency of the DNBA material (40.8 mV) is nearly 4.08 times that of KDP (10 mV). From the above observation,
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it is remarkably easy that DNBA crystal potential use in the frequency conversion applications. Conclusion The organic NLO material 2,3-Dimethyl-N-[4-(Nitro) benzylidene] aniline was successfully synthesized and grown the single crystal from the ethyl acetate by slow evaporation technique. Single crystal X-ray diffraction has been carried out to find the unit cell parameter of the grown material. The crystalline nature of the synthesized material was analysed by powder XRD pattern. Confirmation of the molecular and structural was done by NMR, FTIR and FT-Raman, Mass spectrum analysis. From the UV–Visible spectrum of the grown crystal shows low absorbance with cutoff 450 nm in the visible region and shows low absorbance in the entire near IR region. A thermal property of the grown material studied by TG/ DTA analysis and melting point of the material was found to be 141 °C, and the materials were stable up to 250 °C. The SHG relative efficiency was found to be more efficiency 4.08 times than that of standard KDP as a reference material. Thus, the characterizations support the basic and complete suitability of the grown crystal for NLO applications. Acknowledgements The authors acknowledge to STIC-Cochin for XRD facility and P.K. Das IISc-Bangalore for extending Powder SHG measurement. The authors also express thanks to VIT University management for their constant encouragement and financial support.
Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2014.02.084. References [1] D. Sriram, P. Yogeeswari, N.S. Myneedu, V. Saraswat, Bioorg. Med. Chem. Lett. 16 (2006) 2127–2129. [2] M.S. Karthikeyan, D.J. Prasad, B. Boojary, et al., Bioorg. Med. Chem. Lett. 14 (2006) 7482–7489. [3] H.J. Ravindra, W.T.A. Harrison, M.R. Suresh Kumar, S.M. Dharmaprakash, J. Cryst. Growth 311 (2009) 310–315. [4] H.J. Ravindra, A. John Kiran, S.R. Nooji, et al., J. Cryst. Growth 310 (2008) 2543– 2549. [5] S.R. Marder, W.E. Torruellas, M. Blanch Desce, V. Riddi, G.I. Stegeman, Science 276 (1997) 1233–1236. [6] J.L. Bredas, C. Adant, P. Tackx, A.P. Persoons, Chem. Rev 94 (1994) 243–278. [7] P. Audebert, K. Kamada, K. Matsunaga, K. Ohta, Chem. Phys. Lett. 367 (2003) 62–71. [8] A. Karakas, H. Unver, Spectrochim. Acta A 75 (2010) 1492–1496. [9] M.I. Tariq, S. Ahmad, M.N. Tahir, M. Sarfaraz, I. Hussain, Acta Cryst. E66 (2010) o1561. [10] M. Montazerozohori, S.A. Musavi, J. Coord. Chem. 61 (2008) 3934–3942. [11] M. Montazerozohori, S. Joohari, S.A. Musavi, Spectrochim. Acta A 73 (2009) 231–237. [12] S. Pathak, A. Kumar, P. Tandon, J. Mol. Struct. 981 (2010) 1–9. [13] M. Silverstein, G. Clayton Basseler, C. Morill, Spectrometric Identification of Organic Compounds, Wiley, New York, 1981. [14] P. Kalsi, Spectroscopy of Organic Compounds, Wiley Eastern, New Delhi, 1985. [15] V. Venkataramanan, S. Uchil, H.L. Bhat, Bull. Mater. Sci. 17 (1994) 1109–1117. [16] R. Hanumantharao, S. Kalainathan, G. Bhagavannarayana, U. Madhusoodanan, Spectrochim. Acta Part A 103 (2013) 388–399. [17] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Short Communication
Crystal growth and characterization of an organic nonlinear optical single crystal: 2,3-Dimethyl-N-[4-(Nitro) benzylidene] aniline R.K. Balachandar, S. Kalainathan ⇑ Centre for Crystal Growth, SAS, VIT University, Vellore 632 014, Tamil Nadu, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Single crystals of DNBA were grown
by slow evaporation growth technique. The blue emission of the crystal was identified by Photoluminescence spectral analysis. Thermally stable up to 141 °C. SHG efficiency 4.08 times higher than KDP.
a r t i c l e
i n f o
Article history: Received 18 October 2013 Received in revised form 27 January 2014 Accepted 19 February 2014 Available online 12 March 2014 Keywords: Organic compounds Crystal growth Optical properties X-ray diffraction Second harmonic generation
a b s t r a c t An organic nonlinear optical material 2,3-Dimethyl-N-[4-(Nitro) benzylidene] aniline was synthesized by condensation reaction. The single crystals were grown by the slow evaporation technique at room temperature using ethyl acetate as solvent with large in size and having transparent nature. The unit cell parameters were determined and belong to a noncentrosymmetric orthorhombic crystal structure by single crystal X-ray diffraction. The crystalline nature of the synthesized material was recorded by the powder X-ray diffraction pattern. The molecular structure of the grown material was investigated by proton and carbon nuclear magnetic resonance, mass spectrum analysis. Functional groups were identified by the vibration spectrum analysis. The optical absorbance of the grown crystal was ascertained by Ultraviolet–Visible spectrum. Thermal behaviour and stability of the grown material was investigated by thermo gravimetric/differential thermal analysis. The nonlinear optic conversion efficiency was determined by powder technique and found to be 4.08 times greater that of KDP as a standard reference. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Schiff base is an essential class of organic materials that shows considerable crystallizability has been studying various properties such as biological activity and anti-HIV effect [1,2]. The versatile properties of the Schiff base compound have received an excellent deal of attention in the recent years, also studied extensively which ⇑ Corresponding author. Tel.: +91 416 2202350; fax: +91 416 2243092. E-mail address: [email protected] (S. Kalainathan). http://dx.doi.org/10.1016/j.saa.2014.02.084 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
exhibit strong nonlinear optical properties [3,4]. In the recent years, we have reported the crystal structure and crystal growth of some organic nonlinear optical (NLO) materials. Organic materials with highly nonlinear optical susceptibilities are considered to be potential alternatives to the inorganic materials for applications in Photonics and optoelectronics [5–7]. As a result, there is an increasing interest in designing and crystallizing new organic materials with desired linear and nonlinear optical properties. In this work, we report the synthesis of 2,3-Dimethyl-N-[4-(Nitro) benzylidene] aniline (DNBA) a Schiff base compound and single
R.K. Balachandar, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 324–328
crystals were grown in centimetre size. The confirmation of structural and functional group of the title material was characterized by spectroscopic technique. Also, we studied optical, thermal and the second harmonic generation (SHG) behaviour of the materials by powder SHG technique.
325
powder XRD pattern of title crystal (h, k, l) values were indexed using powder X software program and is shown in Fig. 1. 1
H and
13
C NMR spectral analysis
1
Experimental Material synthesis and crystal growth of DNBA An equimolar ratio of 2,3-dimethylaniline (1.22 ml) and 4-Nitrobenzaldehyde (1.51 g) each of 10 mmol were taken in a round bottom flask, refluxed in methanol for 30 min resulting in yellow colour solid precipitates due to the condensation reaction between the two molecules with water as by product. Then filtering the precipitates with filter paper and the crude material were dried at room temperature. The crude material was recrystallized with methanol in order to become purified synthesized material. Fig. S1 in supplementary shows the reaction scheme of the DNBA. The recrystallized material was dissolved in the solvent as ethyl acetate and stirred continuously for 6 h using a magnetic stirrer, and the saturated solution was prepared, filtered and covered tightly with aluminium foil kept undisturbed at room temperature for controlling slow evaporation of the solvent. Natural slow evaporation of the ethyl acetate induces the spontaneous nucleation in the solution, and tiny seed single crystals of optically transparent observe in nature have been occurring after 5 days and resulted larger size single crystal harvested after 10 days. Fig. S2 in supplementary shows the grown DNBA single crystal. Results and discussion Single crystal X-ray diffraction Single crystal XRD study was performed to determine the unit cell parameter of the grown single crystal by using diffractometer-Bruker Kappa Apex II. The single crystal XRD study reveals that the DNBA belongs to non-centrosymmetric orthorhombic system with the space group ‘‘P212121’’, the lattice parameter a = 7.168 Å, b = 11.844 Å, c = 15.374 Å and V = 1305.2 Å, satisfying one of the basic and foremost requirements for the SHG activity of the single crystal material, the obtained unit cell parameter values were in close agreement with those of reported values [8,9]. Table 1 shows the unit cell parameter of the reported and current work of the DNBA.
H and 13C NMR spectrum of the purified DNBA sample were recorded using Bruker 400 MHz instrument in deuterated chloroform (CDCl3) with tetramethylsilane (TMS) as the internal standard. The structure of DNBA containing different types of protons shows distinct peaks as expected at different chemical shift positions from the different environment of the proton. The imine protons (AHC@NA) act as a singlet. The singlet signal at d = 8.436 ppm corresponds to the proton of imine group, which confirms the formation of the Schiff base compound [10,11]. The protons of two methyl (CH3) group attached to the aromatic radicals are observed two separate singlets at d = 2.313 and d = 2.326 ppm respectively. The aromatic shifts of different protons were observed in the various environments, in the region from d = 6.812 to 8.315 ppm which contains two doublet and one triplet. 1 H NMR spectrum of the grown material is shown in supplementary Fig. S3. From 13C NMR of the title compound, the assignment of the each signal is a distinctive carbon environment in the molecule is also identified. The shift (d = 156.42 ppm) is due to the imine group carbon atom which confirms the creation of the Schiff base compound. The signal at d = 149.20 and 149.99 ppm refer to the Nitro group attached to the aromatic carbon atom and the nitrogen (ACH@NAAr) attached to the aromatic ring and from the imine linkage carbon atom. The peaks correspond to the aromatic carbon, which appear on the aromatic parts from (d = 115.13 to 141.97 ppm). The signal (d = 13.97 ppm and d = 20.21 ppm) were expected to the two methyl group carbon atom attached to the aromatic ring and the three-line signal (d = 76.85, 77.16, 77.48 ppm) from the CDCl3 solvent corresponds to the single carbon atom; it appears as a triplet because of an interaction with the deuterium atom. Thus, the molecular structure of the title compound is confirmed from the proton and carbon NMR spectrum. 13C NMR spectrum of title material is shown in supplementary Fig. S4. FTIR and FT-Raman spectral analysis To analysis qualitatively the presence of the functional group in the grown crystal, Fourier Transforms Infrared spectrum (FTIR) was recorded in the solid state as KBr discs technique using a
Powder X-ray diffraction The Fine crushed powder of DNBA single crystal was scanned in the 2h values ranging from 10° to 60°, and the powder X-ray diffraction pattern was recorded with Bruker, D8 Advance model, Cu Ka radiation (k = 1.5406 (Å)). The prominent peaks in the
Table 1 Unit cell parameter of reported and present work of DNBA. Parameters
Reported [6]
Present work
Crystal system Space group a b c V Molecular formula Molecular weight
Orthorhombic P212121 7.1969 (5) Å 11.8023 (7) Å 15.3721 (14) Å 1305.71(14) Å3 C15H15NO 225.2857
Orthorhombic P212121 7.168 ± 0.005 Å 11.844 ± 0.009 Å 15.374 ± 0.009 Å 1305.2 ± 0.4 Å3
Fig. 1. Powder XRD pattern of DNBA.
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HR-Mass spectral analysis A high resolution mass spectrum is shown in supplementary Fig. S5 helps to determine the exact mass of the molecular ion of the compound [14]. The parent molecular ion is often the largest mass which is not fragmented. The calculated molecular weight is 254.2838, and from the mass spectrum, it is observed that the parent ion peak representing the correct mass of the DNBA is to be at 254.2800 (m/z). The mass spectrum also shows other peaks corresponding to fragment ions resulting from the breaking of certain bonds as follows, the peak at 222.2088 (m/z) are due the fragmentation of the Nitro group on the aromatic ring. The peak at 181.3162 (m/z) is due the fragmentation of two methyl and Nitro group group attached to the aromatic ring and the peak at 151.3259 (m/z) is expected to the complete cleavage of the 2,3dimethylaniline from the aldehyde compound. UV–Visible spectral analysis
Fig. 2. FTIR spectrum of the DNBA.
Shimadzu FTIR spectrophotometer in the range of 400–4000 cm 1. Fourier Transform-Raman was recorded in the Bruker RFS, in the range from 50 to 5000 cm 1. The recorded FTIR and F-Raman spectra shown in Figs. 2 and 3. The absorption band assignment to the stretching of C@N bond was observed at frequency 1622 cm 1, and this value confirms with the reported in the FTIR spectrum of Schiff base in the case of FT-Raman it is observed at 1623 cm 1 [12,13]. The aromatic hydrogen absorption band is observed at 3081 and 2978 cm 1 (m CH asymmetry aromatic and m CH symmetry aromatic). In the FT-Raman, it was observed at 3078 and 2913 cm 1. CAC stretching absorptions are absorptions expected around 1597–1512 cm 1 in the FTIR. In the case of FT-Raman observed in 1595–1512 cm 1. With the help of FTIR and FT-Raman spectrum, the presence of the specific functional groups of the title material is confirmed.
The optical absorption spectrum of the grown crystal was recorded using Elico SL218 Double beam UV–Visible spectrophotometer in the wavelength range of 190–1100 nm at room temperature. A sample of 2.33 mm thickness of as grown crystal was used for measurement without polishing the crystal surface. The recorded Ultraviolet–Visible (UV–Visible) absorbance spectrum is shown in Fig. 4. It is observed that the maximum absorbance at 380 nm in the UV region and the cutoff wavelength is 450 nm. The crystal has low absorption starts in the visible and downright reaches a minimum in the NIR region. The high excited-to-ground state dipole moment, which increases the optical nonlinearity also increases the absorption in the UV–Visible spectrum [15]. Also, there is a little absorbance at the frequency doubling wavelength (532 nm), which improves the SHG output. Photoluminescence study The Photoluminescence emission was found by exciting the crystalline powder of the grown material using light of wavelength where maximum absorption was obtained. The PL spectra were recorded using a Jobin Yvon–Spex Spectro-fluorometer (Fluorolog version-3; Model FL3-11) at room temperature. The excitation source used was a Xenon arc lamp (450 W). The detector (PMTR928P) has a flat response from 200 to 900 nm and the spectral
Fig. 3. FT-Raman spectrum of the grown material.
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327
Fig. 6. TG/DTA thermal analysis of the DNBA. Fig. 4. UV–Visible spectrum of the grown material.
resolution of 0.2 nm. The sample is excited at the wavelength of 450 nm chosen from UV–Visible studies. The recorded PL spectrum is shown in Fig. 5. The band gap energy of the material from the highest peak intensity was calculated from the formula Eg = hc/ke. Here, h, c and e are universal constants and the k is the wavelength of the maximum intensity. The calculated band gap energy is about Eg = 2.567 eV and Eg = 2.52 eV (at two emission peak 483 nm and 493 nm). From the PL spectrum, it is concluded that it shows two peaks with a peak wavelength at 483 nm and 492 nm which emits blue emission [16]. Thermal analysis The thermal stability of the grown crystal was measured by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) simultaneously using Netzsch STA 409 PL Luxx. Fig. 6 shows the TG/DTA thermal analysis of the grown material. A powder
sample of weighing about 11.662 mg was taken in an alumina crucible was used for heating the sample. The study was carried out in the nitrogen atmosphere at the heating rate of 10 K/min over from the room temperature to 500 °C. From DTA thermogram that an endothermic event begins at 136 °C and the sharpness of peak appears at 141 °C which is due to the melting point of the sample. The sharpness of the endothermic peak indicates that considerable crystalline nature and purity of the material were clearly observed from thermal analysis. Solid–liquid phase transition observed in the during the melting point, and up to 225 °C before the decomposition of the material and there is no other transition noticed. From TG curve, it is observed that the material does not sublime and is stable up to 225 °C. A peak at 353 °C shows the entire decomposition of the grown material. About 6.33% of carbon residues were present. From the thermal analysis, it is concluded that the material is quite stable up to 141 °C, and it could be expected utility of any suitable applications up to this temperature. Powder SHG measurement
Fig. 5. PL spectrum of the DNBA.
The grown crystals were characterized one of the optical studies by second harmonic generation efficiency. NLO efficiency was carried out by Kurtz and Perry powder technique to determine the materials with non-centrosymmetric crystal structure. Both DNBA and KDP crystal were powdered to uniform particle size in order to make relative comparisons with known KDP SHG materials [17]. The crystalline powder sample was filled airtight with microcapillary tubes of uniform bore of about 1.5 mm in diameter. A high intensity pulsed Nd:YAG laser of wavelength 1064 nm with input beam energy 3.8 mJ/pulse and pulse width 10 ns with a repetition rate of 10 Hz were used. The crystalline powdered samples with a uniform particle in the micro-Capillary tube were exposed to the laser radiation. The second harmonic signal was generated from crystalline powder sample was confirmed by the bright green light emission (k = 532 nm) was observed which indicates the SHG behaviour of the DNBA material, was detected by a photomultiplier tube (PMT) and viewed on the oscilloscope (CRO). The optical signal fed into the PMT was converted into voltage output at the CRO. The value obtained in the CRO was compared with the voltage output for a standard KDP sample. The ratio of the two values gives the relative SHG efficiency of the DNBA material (40.8 mV) is nearly 4.08 times that of KDP (10 mV). From the above observation,
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it is remarkably easy that DNBA crystal potential use in the frequency conversion applications. Conclusion The organic NLO material 2,3-Dimethyl-N-[4-(Nitro) benzylidene] aniline was successfully synthesized and grown the single crystal from the ethyl acetate by slow evaporation technique. Single crystal X-ray diffraction has been carried out to find the unit cell parameter of the grown material. The crystalline nature of the synthesized material was analysed by powder XRD pattern. Confirmation of the molecular and structural was done by NMR, FTIR and FT-Raman, Mass spectrum analysis. From the UV–Visible spectrum of the grown crystal shows low absorbance with cutoff 450 nm in the visible region and shows low absorbance in the entire near IR region. A thermal property of the grown material studied by TG/ DTA analysis and melting point of the material was found to be 141 °C, and the materials were stable up to 250 °C. The SHG relative efficiency was found to be more efficiency 4.08 times than that of standard KDP as a reference material. Thus, the characterizations support the basic and complete suitability of the grown crystal for NLO applications. Acknowledgements The authors acknowledge to STIC-Cochin for XRD facility and P.K. Das IISc-Bangalore for extending Powder SHG measurement. The authors also express thanks to VIT University management for their constant encouragement and financial support.
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