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Studies on growth and characterization of nonlinear optical material 4-chloro-4′methoxy benzylideneaniline: A Schiff base organic material
Arabian Journal of Chemistry (2014) xxx, xxx–xxx
King Saud University
Arabian Journal of Chemistry www.ksu.edu.sa www.sciencedirect.com
ORIGINAL ARTICLE
Studies on growth and characterization of nonlinear optical material 4-chloro-40methoxy benzylideneaniline: A Schiff base organic material S. Leela a,b, T. Deepa Rani c, A. Subashini b, S. Brindha b, R. Ramesh Babu b, K. Ramamurthi d,* a
Department of Physics, Ethiraj College for Women, Chennai 600008, Tamilnadu, India Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamilnadu, India c Department of Physics, Kongu Engineering College, Perundurai 638052, Erode, Tamilnadu, India d Crystal Growth and Thin Film Laboratory, Department of Physics and Nanotechnology, Faculty of Engineering and Technology, SRM University, Kattankulathur 603203, Tamilnadu, India b
Received 24 May 2013; accepted 28 June 2014
KEYWORDS Organic compounds; Crystal growth; Two photon absorption; Dielectric studies
Abstract Nonlinear optical material, 4-chloro-40 methoxy benzylideneaniline (CMOBA) was synthesized and single crystal of CMOBA was grown by slow evaporation method. Functional groups of CMOBA were identified using the Fourier transform infrared spectral analysis and the molecular structure was confirmed by 1H and 13C NMR spectral analyses. Grown crystal was subjected to single crystal X-ray diffraction analysis to obtain unit cell parameters. UV–Vis-NIR optical study revealed that the UV cut off occurs at the wavelength of about 390 nm and the crystal is transparent in the wavelength range of 400–1100 nm. Second harmonic generation efficiency of the powdered CMOBA is about 3.7 times that of potassium dihydrogen orthophosphate. By using open aperture Z-scan (Nd:YAG, 532 nm, 5 ns) the measured effective two-photon absorption coefficient b was 3 · 1012 m/W. The melting point of the material is 125 C. The dielectric constant and dielectric loss were estimated for various frequencies at different temperatures. ª 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University.
* Corresponding author. Tel.: +91 44 27417400; fax: +91 44 2745 3622. E-mail addresses: [email protected], ramamurthi.k@ktr. srmuniv.ac.in (K. Ramamurthi). Peer review under responsibility of King Saud University.
Production and hosting by Elsevier
1. Introduction Crystal engineering is the art of designing functional molecular solids and it has been actively investigated for its potential exploitation for the synthesis of technologically important materials (Evans and Lin, 2002; Desiraju, 1989; Lehn, 1995; Schmidt, 1971; Gavezzotti, 1994). The nonlinear optical (NLO) process requires materials that manipulate the amplitude, phase, polarization and frequency of optical beams.
http://dx.doi.org/10.1016/j.arabjc.2014.06.008 1878-5352 ª 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University. Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
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S. Leela et al.
Organic materials play a crucial role in the field of nonlinear optics because of the presence of delocalized electronic structure (Zyss, 1993). Particularly, p-conjugated systems containing electron donor (D) and acceptor (A) groups show a large NLO response (Paul and Curtin, 1973; Zyss et al., 1981, 1984). An organic molecule should possess large second-order hyper-polarizability (b) to exhibit good non-linear optical properties and b can be enhanced by increasing the intra-molecular charge transfer interaction and by extending the size of p-conjugated system (Eaton et al., 1987; Tsunekawa et al., 1990; Huijts and Hesselink, 1989; Rozwadowski et al., 1999). Benzylideneaniline (BA) derivatives are successful examples for producing high non-linear optically active crystals. 4-nitro40 methyl benzylidene aniline (NMBA) (Srinivasan et al., 2000), 4-nitro-40 methoxy benzylidene aniline (NMOBA) (Azariah et al., 2004), 4-chloro-40 dimethylamino benzylidene aniline (CDMABA) (Leela et al., 2009), 4-methoxy-40 dimethylamino benzylidene aniline (MDMABA) (Leela et al., 2010), 4-bromo-40 chloro benzylideneaniline (BCBA) and 4-chloro40 chloro benzylideneaniline (CCBA) (Subashini et al., 2011a,b), 4-bromo-40 dimethylamino benzylideneaniline (BDMABA) and 4-bromo-40 nitro benzylideneaniline (BNBA) (Subashini et al., 2013a) are some of the reported BA derivatives. NMBA and NMOBA are the reported second order NLO materials and CDMABA, MDMABA, BCBA, CCBA and BDMABA are reported for their third order NLO optical properties. BNBA material exhibits both second order and third order NLO optical properties. By mesomeric effect, both chloro and methoxy groups are electron donor. In this work, one of the benzylidene aniline derivatives 4-chloro-40 methoxy benzylidene aniline (CMOBA) was synthesized. The single crystal of CMOBA was grown and characterized for its structural, thermal, linear and nonlinear optical properties. CMOBA crystallizes in the noncentrosymmetric space group and it exhibits second and third order nonlinear optical properties.
Figure 1
Harvested crystal of CMOBA.
sample was shinny. Thin layer chromatography (TLC) studies confirmed that the synthesized material consists of single compound. Important factor that influences the habit of growing crystal is the polarity of the solvents (Lide, 1999). Hence, in this study a few organic solvents were employed to identify the reasonable solvent. Various solvents having different dipole moments such as methanol, ethylacetate and acetonitrile and their mixed solvents were employed to study their influence on the growth habits of CMOBA crystal. The mixed solvent of ethanol and ethyl acetate yielded relatively good transparent crystal. Hence the single crystals of CMOBA have been grown from saturated solution of the synthesized salt employing the mixed solvent of ethanol and ethyl acetate by the slow evaporation at room temperature. Transparent single crystal of dimension 6 · 4 · 2 mm3 was grown in a growth period of twenty one days and is shown in Fig. 1. 3. Results and discussion
2. Experimental
3.1. FTIR spectral analysis
2.1. Preparation and growth of CMOBA
The Fourier transform infrared (FTIR) spectrum recorded for the CMOBA material using a Perkin Elmer-Paragon – 500 FTIR spectrometer is given in Fig. 2. The spectrum was recorded by the KBr pellet technique between the range of 400 and 4000 cm1 and the presence of various functional groups was confirmed. Benzylideneaniline displays the C‚N stretching at 1613 cm1 (Kemp, 1993) and the imine CAH in-plane bending is observed at 1362 cm-1. Para-di-substituted benzenes show the CAH deformation vibration in the region 840–800 cm1. In this work the CAH deformation vibration appears at 833 cm1. CAH in-plane and out-of-plane bending vibrations of the phenyl ring are observed at 1025, 1094, 1176, 1247 and 1297 cm1 and 761 and 833 cm1, respectively
CMOBA was synthesized by the condensation reaction between p-chlorobenzaldehyde (p-CB) and p-methoxyaniline (p-MOA) in equimolar ratio (Ren et al., 2008). The schematic representation for the synthesis of CMOBA is depicted in Scheme 1. The reaction mixture was refluxed for about 8 h and the solution was filtered using the Whatman filter paper and the resulting product of 4-chloro-40 methoxy benzylideneaniline was obtained. The purity of the synthesized salt was improved by successive recrystallization process in ethanol. Activated charcoal was added during the recrystallization process for removing colored impurities and the purified CHO
NH2
-H2O
+
Cl
N
C
OCH3
H Cl
OCH3
Scheme 1
Schematic diagram for the synthesis of CMOBA.
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
Studies on growth and characterization of 4-chloro-40 methoxy benzylideneaniline
FTIR spectrum of CMOBA.
Figure 2
(Silverstein et al., 1981). The absence of the vibrational frequency of the NAH and C‚O groups in the FTIR spectrum also confirms the formation of the imine group (Kemp, 1993). Thus the FTIR spectral analysis confirms the formation of the CMOBA. 3.2. NMR spectral analyses In the present study, Nuclear Magnetic Resonance (NMR) spectral analysis, a powerful tool to derive the structural information from the synthesized compound, was carried out on
Figure 3a
3
the purified CMOBA sample. The 1H and 13C NMR spectra of the CMOBA were recorded by employing a Bruker AC 400 MHz NMR spectrometer in CDCl3. In the 1H NMR spectrum, the singlet at 8.423 ppm confirms the formation of Schiff base compounds containing the imine (CH‚N) group. The adjacent four doublet protons are due to the aromatic rings proton. The signal at 3.820 ppm corresponds to three protons of the methoxy group of the aniline phenyl ring moiety. The presence of protons in the CMOBA material is shown in Fig. 3a. In the NMR spectrum of CMOBA, the ratio of steps obtained is as follows,
1
H NMR spectrum of CMOBA.
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
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S. Leela et al.
Figure 3b
A: 1:
B: 2:
C: 2:
D: 2:
E: 2:
13
C NMR spectrum of CMOBA.
F 3
Thus, the number of protons associated with the signals are A-1H; B, C, D and E-2H; and F-3H, respectively. The CMOBA peaks are compared with 4-nitro-40 methoxy benzylideneaniline (NMOBA) crystal. Substitution of the chloro group at the para-postion of benzaldehyde causes shielding effect of imine, methoxy and aromatic ring protons when compared to NMOBA. For NMOBA two proton doublet (ortho to nitro) at 8:1 ppm and CMOBA chemical shift at 7.8. Generally the nitro group has strong electron withdrawing nature when compared to the chloro group so chemical shift slightly changed. The common range of energy absorption for 13C is wide (d 0-200) relative to tetramethylsilane (TMS). In the 13C NMR spectrum (proton decoupled) each magnetically non-equivalent carbon gives a single unsplit peak. The spectrum (Fig. 3b) shows the placement of carbon atoms in the CMOBA material. The imine group carbon atom (C‚N) at 156.65 ppm (signal B) appears as singlet peak and C‚N peak position well coincide with the reported literature value (Neuvonen et al., 2006) which confirms the formation of Schiff base compound. The chemical shift at 55.49 ppm is attributed to the methoxy (OCH3) (signal K) group. The peak at 158.51 ppm is due to = CAOCH3 which belongs to the aromatic ring carbons. The signals at A, C, D, E, F, G, H and I are due to aromatic ring carbon. The signal at J is due to the solvent. Thus the molecular structure of CMOBA is confirmed by proton and carbon NMR analyses.
Figure 4
UV–vis-NIR Transmission spectrum of CMOBA.
b = 7.357 A˚ (7.3392 A˚) and c = 27.555 A˚ (27.469 A˚) and these values compare well with the corresponding values of the earlier work (Ren et al., 2008) given in the parentheses. 3.4. Linear optical property
3.3. Single crystal X-ray diffraction
3.4.1. UV–vis-NIR transmittance
Single crystal X-ray diffraction study was carried out using a single crystal diffractometer CAD4/MACH 3 which shows that CMOBA crystallizes in the orthorhombic crystal system. The recorded unit cell parameters are a = 6.102 A˚ (6.155 A˚),
In order to understand the optical transparency in the UV– vis-NIR region of the electromagnetic spectrum, the optical transmittance study was carried out for the CMOBA crystal of thickness 2 mm. In this study the transmittance of the sample, which is the descriptive result of absorption, was
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
Studies on growth and characterization of 4-chloro-40 methoxy benzylideneaniline
5
the frequency was confirmed by the emission of green radiation of wavelength 532 nm which was collected by a monochromator after separating the 1064 nm pump beam with an IR-blocking filter. The SHG efficiency of CMOBA is about 3.7 times that of potassium dihydrogen orthophosphate (KDP) and is relatively larger than that of NMOBA which is about 1.3 times that of KDP. 3.5.2. Z-scan studies
3.5.1. Second harmonic studies
The nonlinear absorption of CMOBA was studied using the single beam Z-scan studies. To measure the optical nonlinearity, open aperture Z-scan measurements were done at 532 nm using 5 ns laser pulses from a frequency-doubled Nd:YAG laser (Quanta Ray-Spectra Physics). For this measurement the sample was dissolved in chloroform and excited with laser and the pulse energy used is 90 lJ. The laser beam is focused using a lens, and the sample is translated along the beam axis (z-axis) through the focal region over a distance several times that of the diffraction length. At each position z the sample sees different laser intensities, and the position dependent (i.e., intensity-dependent) transmission is measured using an energy meter placed after the sample. Fig. 5 shows the open aperture Z-scan of CMOBA. The Z-scan curves obtained are numerically fitted to the nonlinear transmission equation for a two-photon absorption process (Sutherland, 1996) given by Z þ1 1 2 T ¼ pffiffiffi lnð1 þ q0 et Þdt pq0 1
Second harmonic generation (SHG) test on the CMOBA was performed by the Kurtz and Perry powder SHG method (Kurtz and Perry, 1968). The crystal was powdered and inserted in a microcapillary tube, then the sample was illuminated using a Q-switched, mode locked Nd:YAG laser with modulated radiation corresponding to the first harmonic output of 1064 nm with a pulse width of 8 ns. Doubling of
where a is the linear absorption coefficient. q0 is given by b(1 R)I0Leff, where b is the nonlinear absorption coefficient and I0 is the on-axis peak intensity. Leff is given by [1 exp(aL)]/a, where L is the sample length. Measured two-photon absorption coefficient of CMOBA is 3 · 1012 m/ W. Under similar excitation conditions, one of the benzylideneaniline derivative materials 4-bromo-40 dimethylamino
Figure 5
Open aperture Z-scan of CMOBA.
recorded at room temperature. The lower cutoff wavelength of the CMOBA starts at 390 nm and it shows the wider range of the optical transparency. The crystal is transparent in the visible region of 400–1100 nm wavelength as shown in Fig. 4. 3.5. Nonlinear optical properties
Figure 6a
TGA/DTA curve of CMOBA.
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
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Figure 6b
DSC curve of CMOBA.
benzylideneaniline (Subashini et al., 2013) exhibits the effective TPA coefficient value in the range of about 1012 m/W. 3.6. Thermal analyses The thermogravimetric and differential thermal analyses (TG/ DTA) of CMOBA was carried out between 30 and 1200 C at a heating rate of 20 C/min using TA instruments Model SDT Q 600 in the nitrogen atmosphere and is given in Fig. 6a. The
Figure 7a
material is stable up to 177 C and the major weight loss (97.78%) is observed in the temperature range of 178–285 C. Single stage weight loss is observed in the TG curve. A sharp endothermic peak at 125 C corresponds to the melting point in DTA. The sharpness of the peak confirms the good crystallinity of the synthesized compound. The differential scanning calorimetry (DSC) study was performed with 3.033 mg of CMOBA using TA instruments Model SDT Q 600 in the temperature range of 27–1200 C at a heating rate of 20 C/min
Dielectric constant and loss vs. frequency of CMOBA.
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
Studies on growth and characterization of 4-chloro-40 methoxy benzylideneaniline
Figure 7b
7
Dielectric constant and loss vs. temperature of CMOBA.
in the nitrogen atmosphere. The CMOBA material melts at 125 C (Fig. 6b) and the value agrees well with the DTA.
Fig. 7b. These curves suggest that the dielectric constant and dielectric loss strongly depend on the frequency of the applied field (Hill et al., 1969; Rao and Smakula, 1965).
3.7. Dielectric studies 4. Conclusion Dielectric properties are correlated with the electro-optical property of the crystals. The measurement of dielectric properties provides information on materials (Hiremath and Venkataraman, 2003). Carefully discerned sample of CMOBA was cut and polished and coated by the ohmic contact to make the sample as a parallel plate capacitor. Agilent Model LCR meter was used to measure the capacitance and dielectric loss (tan d) of the sample as a function of frequency (100 Hz to 1 MHz) in the temperature range of 60–100 C. The dielectric constant was calculated using the relation er ¼ ½Ccrys Cair ð1 Acry =Aair Þ=Cair x½Aair =Acry where Ccrys and Cair are the capacitance of the crystal and air respectively, and Acry and Aair are the area of the crystal and air respectively. The maximum dielectric constant measured at 100 C for the CMOBA crystal is 82 for 1 KHz and this value decreases to 55 for 1 MHz as shown in Fig. 7a. It is observed that the dielectric constant of the crystal at higher frequencies is almost constant. At lower frequencies, the dielectric constant was considerably higher than that at higher frequencies. This can be attributed to the interfacial polarization in which the mobile charge carriers are impeded by a physical barrier that inhibits producing a localized polarization of the material. This type of dielectric response revealed is of great interest in applications in which materials with high dielectric constant values are good candidates for heating devices (Sankar et al., 2007). The magnitude of dielectric constant (er) depends on the degree of polarization. The dielectric constant of CMOBA crystal measured at 100 C is 130 for 1 KHz and this value decreases to 93 for 1 MHz as shown in
Optical quality single crystals of CMOBA were grown at room temperature using the solution growth technique. From the FTIR and NMR spectra, the formation of the imine group of the material was confirmed. The cell parameters estimated in this work compare well with the corresponding reported values. The UV–vis-NIR spectrum elucidates that the crystal is transparent between 400 and 1100 nm which shows its applicability for NLO applications. The SHG efficiency of the powdered CMOBA crystal is about 3.7 times that of KDP. The measured effective two-photon absorption coefficient is 3 · 1012 m/W. Thermal analyses indicate that the crystal has good thermal stability. A sharp peak observed at 125 C in the DSC curve corresponds to the melting of the material. Frequency dependent nature of dielectric properties is brought out. Acknowledgements One of the authors (SL) is grateful to Dr. A. Ilangovan, School of Chemistry, Bharathidasan University, Tiruchirappalli for fruitful discussion and Dr. Reji Philip, RRI Bangalore for Z-scan measurements. The authors thank the University Grant Commission, Government of India [File No. 32–37/2007 (SR)] for financial assistance. References Azariah, A.N., Hameed, A.S.H., Thennappan, T., Noel, M., Ravi, G., 2004. Mater. Chem. Phys. 88, 90.
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
8 Desiraju, G.R., 1989. Crystal Engineering: The Design of Organic Solids. Elsevier, New York. Eaton, D.F., Anderson, A.G., Tam, W., Wang, Y., 1987. J. Am. Chem. Soc. 109, 1886. Evans, O.R., Lin, W., 2002. Acc. Chem. Res. 35, 511. Gavezzotti, A., 1994. Acc. Chem. Res. 27, 309. Hill, N.E., Vaughan, W.E., Price, A.H., Davies, M., 1969. Dielectric Properties and Molecular Behavior. Van Nostrand Reinhold, London. Hiremath, V.A., Venkataraman, A., 2003. Bull. Mater. Sci. 26, 391. Huijts, R.A., Hesselink, G.L.J., 1989. Chem. Phys. Lett. 156, 209. Kemp, W., 1993. Organic Spectroscopy, third ed. ELBS, Macmillan, London. Kurtz, S.K., Perry, T.T., 1968. J. Appl. Phys. 39, 3798. Leela, S., Ramamurthi, K., Bhagavannarayana, G., 2009. Spectrochim. Acta 74A, 78. Leela, S., Hema, R., Evans, H.S., Ramamurthi, K., Bhagavannarayana, G., 2010. Spectrochim. Acta 77A, 927. Lehn, J.M., 1995. Supramolecular Chemistry: Concepts and Perspectives. VCH Publishers, New York. Lide, D.R., 1999. Handbook of Chemistry and Physics, 80th ed. CRC Press LLC. Neuvonen, H., Neuvonen, K., Fulop, F., 2006. J. Org. Chem. 71, 3141. Paul, I.C., Curtin, D.Y., 1973. Acc. Chem. Rev. 7, 217. Rao, K.V., Smakula, A., 1965. J. Appl. Phys. 36, 2031. Ren, X.Y., Ding, Y.F., Jiana, F.F., 2008. Acta Cryst. E64, o1793. Rozwadowski, Z., Majewski, E., Dziembowska, T., Hansen, P.E., 1999. J. Chem. Soc. Perkin Trans. 2, 2809.
S. Leela et al. Sankar, R., Raghavan, C.M., Balaji, M., Mohan Kumar, R., Jayavel, R., 2007. Cryst. Growth Des. 7, 348. Schmidt, G.M.J., 1971. Photodimerization Solid-State Pure Appl. Chem. 27, 647. Silverstein, M., Clayton Basseler, G., Morill, C., 1981. Spectrometric Identification of Organic Compounds. Wiley, New York. Srinivasan, K., Sankaranarayanan, K., Thangavelu, S., Ramasamy, P., 2000. J. Cryst. Growth 212, 246. Subashini, A., Kumaravel, R., Leela, S., Stoeckli-Evans, Helen., Sastikumar, D., Ramamurthi, K., 2011a. Spectrochim. Acta 78A, 935. Subashini, A., Bhagavannarayana, G., Ramamurthi, K., 2011b. Spectrochim. Acta 82A, 91. Subashini, A., Bhagavannarayana, G., Ramamurthi, K., 2013a. Spectrochim. Acta 104A, 403. Subashini, A., Leela, S., Ramamurthi, K., Arakcheeva, A., Helen Stoeckli-Evans, Petricek, V., Chapuis, G., Pattison, P., Reji Philip, 2013. Cryst. Eng. Commun. 15, 2474. Sutherland, R.L., 1996. Handbook of Nonlinear Optics. Marcel Dekkar, New York. Tsunekawa, T., Gotoh, T., Iwamoto, M., 1990. Chem. Phys. Lett. 166, 353. Zyss, J., 1993. J. Phys. D Appl. Phys. 26, 8198. Zyss, J., Chemla, D.S., Nicoud, I.F., 1981. J. Chem. Phys. 74, 4800. Zyss, J., Nicou, J.F., Coquillay, M., 1984. J. Chem. Phys. 81, 4160.
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
King Saud University
Arabian Journal of Chemistry www.ksu.edu.sa www.sciencedirect.com
ORIGINAL ARTICLE
Studies on growth and characterization of nonlinear optical material 4-chloro-40methoxy benzylideneaniline: A Schiff base organic material S. Leela a,b, T. Deepa Rani c, A. Subashini b, S. Brindha b, R. Ramesh Babu b, K. Ramamurthi d,* a
Department of Physics, Ethiraj College for Women, Chennai 600008, Tamilnadu, India Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamilnadu, India c Department of Physics, Kongu Engineering College, Perundurai 638052, Erode, Tamilnadu, India d Crystal Growth and Thin Film Laboratory, Department of Physics and Nanotechnology, Faculty of Engineering and Technology, SRM University, Kattankulathur 603203, Tamilnadu, India b
Received 24 May 2013; accepted 28 June 2014
KEYWORDS Organic compounds; Crystal growth; Two photon absorption; Dielectric studies
Abstract Nonlinear optical material, 4-chloro-40 methoxy benzylideneaniline (CMOBA) was synthesized and single crystal of CMOBA was grown by slow evaporation method. Functional groups of CMOBA were identified using the Fourier transform infrared spectral analysis and the molecular structure was confirmed by 1H and 13C NMR spectral analyses. Grown crystal was subjected to single crystal X-ray diffraction analysis to obtain unit cell parameters. UV–Vis-NIR optical study revealed that the UV cut off occurs at the wavelength of about 390 nm and the crystal is transparent in the wavelength range of 400–1100 nm. Second harmonic generation efficiency of the powdered CMOBA is about 3.7 times that of potassium dihydrogen orthophosphate. By using open aperture Z-scan (Nd:YAG, 532 nm, 5 ns) the measured effective two-photon absorption coefficient b was 3 · 1012 m/W. The melting point of the material is 125 C. The dielectric constant and dielectric loss were estimated for various frequencies at different temperatures. ª 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University.
* Corresponding author. Tel.: +91 44 27417400; fax: +91 44 2745 3622. E-mail addresses: [email protected], ramamurthi.k@ktr. srmuniv.ac.in (K. Ramamurthi). Peer review under responsibility of King Saud University.
Production and hosting by Elsevier
1. Introduction Crystal engineering is the art of designing functional molecular solids and it has been actively investigated for its potential exploitation for the synthesis of technologically important materials (Evans and Lin, 2002; Desiraju, 1989; Lehn, 1995; Schmidt, 1971; Gavezzotti, 1994). The nonlinear optical (NLO) process requires materials that manipulate the amplitude, phase, polarization and frequency of optical beams.
http://dx.doi.org/10.1016/j.arabjc.2014.06.008 1878-5352 ª 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University. Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
2
S. Leela et al.
Organic materials play a crucial role in the field of nonlinear optics because of the presence of delocalized electronic structure (Zyss, 1993). Particularly, p-conjugated systems containing electron donor (D) and acceptor (A) groups show a large NLO response (Paul and Curtin, 1973; Zyss et al., 1981, 1984). An organic molecule should possess large second-order hyper-polarizability (b) to exhibit good non-linear optical properties and b can be enhanced by increasing the intra-molecular charge transfer interaction and by extending the size of p-conjugated system (Eaton et al., 1987; Tsunekawa et al., 1990; Huijts and Hesselink, 1989; Rozwadowski et al., 1999). Benzylideneaniline (BA) derivatives are successful examples for producing high non-linear optically active crystals. 4-nitro40 methyl benzylidene aniline (NMBA) (Srinivasan et al., 2000), 4-nitro-40 methoxy benzylidene aniline (NMOBA) (Azariah et al., 2004), 4-chloro-40 dimethylamino benzylidene aniline (CDMABA) (Leela et al., 2009), 4-methoxy-40 dimethylamino benzylidene aniline (MDMABA) (Leela et al., 2010), 4-bromo-40 chloro benzylideneaniline (BCBA) and 4-chloro40 chloro benzylideneaniline (CCBA) (Subashini et al., 2011a,b), 4-bromo-40 dimethylamino benzylideneaniline (BDMABA) and 4-bromo-40 nitro benzylideneaniline (BNBA) (Subashini et al., 2013a) are some of the reported BA derivatives. NMBA and NMOBA are the reported second order NLO materials and CDMABA, MDMABA, BCBA, CCBA and BDMABA are reported for their third order NLO optical properties. BNBA material exhibits both second order and third order NLO optical properties. By mesomeric effect, both chloro and methoxy groups are electron donor. In this work, one of the benzylidene aniline derivatives 4-chloro-40 methoxy benzylidene aniline (CMOBA) was synthesized. The single crystal of CMOBA was grown and characterized for its structural, thermal, linear and nonlinear optical properties. CMOBA crystallizes in the noncentrosymmetric space group and it exhibits second and third order nonlinear optical properties.
Figure 1
Harvested crystal of CMOBA.
sample was shinny. Thin layer chromatography (TLC) studies confirmed that the synthesized material consists of single compound. Important factor that influences the habit of growing crystal is the polarity of the solvents (Lide, 1999). Hence, in this study a few organic solvents were employed to identify the reasonable solvent. Various solvents having different dipole moments such as methanol, ethylacetate and acetonitrile and their mixed solvents were employed to study their influence on the growth habits of CMOBA crystal. The mixed solvent of ethanol and ethyl acetate yielded relatively good transparent crystal. Hence the single crystals of CMOBA have been grown from saturated solution of the synthesized salt employing the mixed solvent of ethanol and ethyl acetate by the slow evaporation at room temperature. Transparent single crystal of dimension 6 · 4 · 2 mm3 was grown in a growth period of twenty one days and is shown in Fig. 1. 3. Results and discussion
2. Experimental
3.1. FTIR spectral analysis
2.1. Preparation and growth of CMOBA
The Fourier transform infrared (FTIR) spectrum recorded for the CMOBA material using a Perkin Elmer-Paragon – 500 FTIR spectrometer is given in Fig. 2. The spectrum was recorded by the KBr pellet technique between the range of 400 and 4000 cm1 and the presence of various functional groups was confirmed. Benzylideneaniline displays the C‚N stretching at 1613 cm1 (Kemp, 1993) and the imine CAH in-plane bending is observed at 1362 cm-1. Para-di-substituted benzenes show the CAH deformation vibration in the region 840–800 cm1. In this work the CAH deformation vibration appears at 833 cm1. CAH in-plane and out-of-plane bending vibrations of the phenyl ring are observed at 1025, 1094, 1176, 1247 and 1297 cm1 and 761 and 833 cm1, respectively
CMOBA was synthesized by the condensation reaction between p-chlorobenzaldehyde (p-CB) and p-methoxyaniline (p-MOA) in equimolar ratio (Ren et al., 2008). The schematic representation for the synthesis of CMOBA is depicted in Scheme 1. The reaction mixture was refluxed for about 8 h and the solution was filtered using the Whatman filter paper and the resulting product of 4-chloro-40 methoxy benzylideneaniline was obtained. The purity of the synthesized salt was improved by successive recrystallization process in ethanol. Activated charcoal was added during the recrystallization process for removing colored impurities and the purified CHO
NH2
-H2O
+
Cl
N
C
OCH3
H Cl
OCH3
Scheme 1
Schematic diagram for the synthesis of CMOBA.
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Studies on growth and characterization of 4-chloro-40 methoxy benzylideneaniline
FTIR spectrum of CMOBA.
Figure 2
(Silverstein et al., 1981). The absence of the vibrational frequency of the NAH and C‚O groups in the FTIR spectrum also confirms the formation of the imine group (Kemp, 1993). Thus the FTIR spectral analysis confirms the formation of the CMOBA. 3.2. NMR spectral analyses In the present study, Nuclear Magnetic Resonance (NMR) spectral analysis, a powerful tool to derive the structural information from the synthesized compound, was carried out on
Figure 3a
3
the purified CMOBA sample. The 1H and 13C NMR spectra of the CMOBA were recorded by employing a Bruker AC 400 MHz NMR spectrometer in CDCl3. In the 1H NMR spectrum, the singlet at 8.423 ppm confirms the formation of Schiff base compounds containing the imine (CH‚N) group. The adjacent four doublet protons are due to the aromatic rings proton. The signal at 3.820 ppm corresponds to three protons of the methoxy group of the aniline phenyl ring moiety. The presence of protons in the CMOBA material is shown in Fig. 3a. In the NMR spectrum of CMOBA, the ratio of steps obtained is as follows,
1
H NMR spectrum of CMOBA.
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Figure 3b
A: 1:
B: 2:
C: 2:
D: 2:
E: 2:
13
C NMR spectrum of CMOBA.
F 3
Thus, the number of protons associated with the signals are A-1H; B, C, D and E-2H; and F-3H, respectively. The CMOBA peaks are compared with 4-nitro-40 methoxy benzylideneaniline (NMOBA) crystal. Substitution of the chloro group at the para-postion of benzaldehyde causes shielding effect of imine, methoxy and aromatic ring protons when compared to NMOBA. For NMOBA two proton doublet (ortho to nitro) at 8:1 ppm and CMOBA chemical shift at 7.8. Generally the nitro group has strong electron withdrawing nature when compared to the chloro group so chemical shift slightly changed. The common range of energy absorption for 13C is wide (d 0-200) relative to tetramethylsilane (TMS). In the 13C NMR spectrum (proton decoupled) each magnetically non-equivalent carbon gives a single unsplit peak. The spectrum (Fig. 3b) shows the placement of carbon atoms in the CMOBA material. The imine group carbon atom (C‚N) at 156.65 ppm (signal B) appears as singlet peak and C‚N peak position well coincide with the reported literature value (Neuvonen et al., 2006) which confirms the formation of Schiff base compound. The chemical shift at 55.49 ppm is attributed to the methoxy (OCH3) (signal K) group. The peak at 158.51 ppm is due to = CAOCH3 which belongs to the aromatic ring carbons. The signals at A, C, D, E, F, G, H and I are due to aromatic ring carbon. The signal at J is due to the solvent. Thus the molecular structure of CMOBA is confirmed by proton and carbon NMR analyses.
Figure 4
UV–vis-NIR Transmission spectrum of CMOBA.
b = 7.357 A˚ (7.3392 A˚) and c = 27.555 A˚ (27.469 A˚) and these values compare well with the corresponding values of the earlier work (Ren et al., 2008) given in the parentheses. 3.4. Linear optical property
3.3. Single crystal X-ray diffraction
3.4.1. UV–vis-NIR transmittance
Single crystal X-ray diffraction study was carried out using a single crystal diffractometer CAD4/MACH 3 which shows that CMOBA crystallizes in the orthorhombic crystal system. The recorded unit cell parameters are a = 6.102 A˚ (6.155 A˚),
In order to understand the optical transparency in the UV– vis-NIR region of the electromagnetic spectrum, the optical transmittance study was carried out for the CMOBA crystal of thickness 2 mm. In this study the transmittance of the sample, which is the descriptive result of absorption, was
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
Studies on growth and characterization of 4-chloro-40 methoxy benzylideneaniline
5
the frequency was confirmed by the emission of green radiation of wavelength 532 nm which was collected by a monochromator after separating the 1064 nm pump beam with an IR-blocking filter. The SHG efficiency of CMOBA is about 3.7 times that of potassium dihydrogen orthophosphate (KDP) and is relatively larger than that of NMOBA which is about 1.3 times that of KDP. 3.5.2. Z-scan studies
3.5.1. Second harmonic studies
The nonlinear absorption of CMOBA was studied using the single beam Z-scan studies. To measure the optical nonlinearity, open aperture Z-scan measurements were done at 532 nm using 5 ns laser pulses from a frequency-doubled Nd:YAG laser (Quanta Ray-Spectra Physics). For this measurement the sample was dissolved in chloroform and excited with laser and the pulse energy used is 90 lJ. The laser beam is focused using a lens, and the sample is translated along the beam axis (z-axis) through the focal region over a distance several times that of the diffraction length. At each position z the sample sees different laser intensities, and the position dependent (i.e., intensity-dependent) transmission is measured using an energy meter placed after the sample. Fig. 5 shows the open aperture Z-scan of CMOBA. The Z-scan curves obtained are numerically fitted to the nonlinear transmission equation for a two-photon absorption process (Sutherland, 1996) given by Z þ1 1 2 T ¼ pffiffiffi lnð1 þ q0 et Þdt pq0 1
Second harmonic generation (SHG) test on the CMOBA was performed by the Kurtz and Perry powder SHG method (Kurtz and Perry, 1968). The crystal was powdered and inserted in a microcapillary tube, then the sample was illuminated using a Q-switched, mode locked Nd:YAG laser with modulated radiation corresponding to the first harmonic output of 1064 nm with a pulse width of 8 ns. Doubling of
where a is the linear absorption coefficient. q0 is given by b(1 R)I0Leff, where b is the nonlinear absorption coefficient and I0 is the on-axis peak intensity. Leff is given by [1 exp(aL)]/a, where L is the sample length. Measured two-photon absorption coefficient of CMOBA is 3 · 1012 m/ W. Under similar excitation conditions, one of the benzylideneaniline derivative materials 4-bromo-40 dimethylamino
Figure 5
Open aperture Z-scan of CMOBA.
recorded at room temperature. The lower cutoff wavelength of the CMOBA starts at 390 nm and it shows the wider range of the optical transparency. The crystal is transparent in the visible region of 400–1100 nm wavelength as shown in Fig. 4. 3.5. Nonlinear optical properties
Figure 6a
TGA/DTA curve of CMOBA.
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Figure 6b
DSC curve of CMOBA.
benzylideneaniline (Subashini et al., 2013) exhibits the effective TPA coefficient value in the range of about 1012 m/W. 3.6. Thermal analyses The thermogravimetric and differential thermal analyses (TG/ DTA) of CMOBA was carried out between 30 and 1200 C at a heating rate of 20 C/min using TA instruments Model SDT Q 600 in the nitrogen atmosphere and is given in Fig. 6a. The
Figure 7a
material is stable up to 177 C and the major weight loss (97.78%) is observed in the temperature range of 178–285 C. Single stage weight loss is observed in the TG curve. A sharp endothermic peak at 125 C corresponds to the melting point in DTA. The sharpness of the peak confirms the good crystallinity of the synthesized compound. The differential scanning calorimetry (DSC) study was performed with 3.033 mg of CMOBA using TA instruments Model SDT Q 600 in the temperature range of 27–1200 C at a heating rate of 20 C/min
Dielectric constant and loss vs. frequency of CMOBA.
Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008
Studies on growth and characterization of 4-chloro-40 methoxy benzylideneaniline
Figure 7b
7
Dielectric constant and loss vs. temperature of CMOBA.
in the nitrogen atmosphere. The CMOBA material melts at 125 C (Fig. 6b) and the value agrees well with the DTA.
Fig. 7b. These curves suggest that the dielectric constant and dielectric loss strongly depend on the frequency of the applied field (Hill et al., 1969; Rao and Smakula, 1965).
3.7. Dielectric studies 4. Conclusion Dielectric properties are correlated with the electro-optical property of the crystals. The measurement of dielectric properties provides information on materials (Hiremath and Venkataraman, 2003). Carefully discerned sample of CMOBA was cut and polished and coated by the ohmic contact to make the sample as a parallel plate capacitor. Agilent Model LCR meter was used to measure the capacitance and dielectric loss (tan d) of the sample as a function of frequency (100 Hz to 1 MHz) in the temperature range of 60–100 C. The dielectric constant was calculated using the relation er ¼ ½Ccrys Cair ð1 Acry =Aair Þ=Cair x½Aair =Acry where Ccrys and Cair are the capacitance of the crystal and air respectively, and Acry and Aair are the area of the crystal and air respectively. The maximum dielectric constant measured at 100 C for the CMOBA crystal is 82 for 1 KHz and this value decreases to 55 for 1 MHz as shown in Fig. 7a. It is observed that the dielectric constant of the crystal at higher frequencies is almost constant. At lower frequencies, the dielectric constant was considerably higher than that at higher frequencies. This can be attributed to the interfacial polarization in which the mobile charge carriers are impeded by a physical barrier that inhibits producing a localized polarization of the material. This type of dielectric response revealed is of great interest in applications in which materials with high dielectric constant values are good candidates for heating devices (Sankar et al., 2007). The magnitude of dielectric constant (er) depends on the degree of polarization. The dielectric constant of CMOBA crystal measured at 100 C is 130 for 1 KHz and this value decreases to 93 for 1 MHz as shown in
Optical quality single crystals of CMOBA were grown at room temperature using the solution growth technique. From the FTIR and NMR spectra, the formation of the imine group of the material was confirmed. The cell parameters estimated in this work compare well with the corresponding reported values. The UV–vis-NIR spectrum elucidates that the crystal is transparent between 400 and 1100 nm which shows its applicability for NLO applications. The SHG efficiency of the powdered CMOBA crystal is about 3.7 times that of KDP. The measured effective two-photon absorption coefficient is 3 · 1012 m/W. Thermal analyses indicate that the crystal has good thermal stability. A sharp peak observed at 125 C in the DSC curve corresponds to the melting of the material. Frequency dependent nature of dielectric properties is brought out. Acknowledgements One of the authors (SL) is grateful to Dr. A. Ilangovan, School of Chemistry, Bharathidasan University, Tiruchirappalli for fruitful discussion and Dr. Reji Philip, RRI Bangalore for Z-scan measurements. The authors thank the University Grant Commission, Government of India [File No. 32–37/2007 (SR)] for financial assistance. References Azariah, A.N., Hameed, A.S.H., Thennappan, T., Noel, M., Ravi, G., 2004. Mater. Chem. Phys. 88, 90.
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Please cite this article in press as: Leela, S. et al., Studies on growth and characterization of nonlinear optical material 4-chloro-40 methoxy benzylideneaniline: A Schiff base organic material. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.06.008