Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 143–147

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Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

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Synthesis, crystal growth and spectroscopic investigation of secondorder organic nonlinear optical single crystal: 2-Chloro-N-[4-(dimethylamino)benzylidene]aniline

1386-1425/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.saa.2013.07.021

⇑ Corresponding author. Tel.: +91 416 2202350; fax: +91 416 2243092.E-mail address: kalainathan@yahoo.com (S. Kalainathan).

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

� First time single crystal of 2Cl4DBAwas grown by slow evaporationtechnique from synthesizedcompound.� NMR, FTIR spectral analysis and XRD

technique were used to confirm theproduct formation.� Good thermal stability of the grown

crystal is up to 135 �C.� SHG efficiency of title crystal was

more than that of standard KDP andurea material.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 12 February 2013Received in revised form 28 June 2013Accepted 16 July 2013Available online 24 July 2013

Keywords:Slow evaporation techniqueNonlinear opticsX-ray diffractionNMROrganic compounds

a b s t r a c t

Organic nonlinear optical (NLO) crystal 2-chloro-N-[4-(dimethylamino)benzylidene]aniline (2Cl4DBA)was synthesized and grown by restricted slow evaporation technique at room temperature using acetoneas solvent with good degree of transparency. The lattice parameters were determined and found to benoncentrosymmetric orthorhombic system by single crystal X-ray diffraction. The crystalline nature ofthe synthesized material was recorded by the powder X-ray diffraction pattern. Molecular structure ofthe grown crystal was investigated by 1H and 13C NMR and functional groups were identified by FTIRspectrum analysis. The optical absorbance of the grown crystal was ascertained by recording UV–Visiblespectrum. Thermal and physiochemical stability of the grown material was investigated by TG/DTAanalysis. SHG efficiency was determined by Kurtz–Perry Powder SHG technique and found to be 4.2and 1.54 times greater that of standard KDP and urea crystals respectively.

� 2013 Elsevier B.V. All rights reserved.

Introduction

Organic nonlinear optical materials (NLO) play a major role innonlinear optics for the fast processing of information and for datastorage applications. Organic NLO materials have been investigateddue to their potentially large nonlinearities and rapid response inelectro-optic effect compared to inorganic NLO materials, largenumbers of molecules were available for investigation. The optical

nonlinearity of the aromatic organic molecules were enhancedwhen the molecule has one donor at the one end and one acceptorgroup bonded at the other end of the conjugated system of themolecule. An organic crystal with delocalized p-electrons usuallydisplays a large NLO response which makes it attractive forapplications in integrated optics [1–3]. Most of the organic crystalsare composed of aromatic molecules that are substituted withelectron donors and acceptors which exhibit intramolecular chargetransfer. In the present investigation, the synthesis of the Schiffbase compound, for the first time we report crystal growth of thetitle compound and its detailed molecular and structural confirma-

144 R.K. Balachandar, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 143–147

tion by spectroscopic techniques. Thermal and second harmonicgeneration efficiency of 2-chloro-N-[4-(dimethylamino)benzyli-dene]aniline single crystals have been studied.

Experimental procedure

Material synthesis

The 2Cl4DBA was synthesized by the condensation reaction be-tween p-aminobenzaldehyde (10 mmol, 1.491 g, aldehyde) and2-chloroaniline (10 mmol, 1.054 ml, primary amine) in an equimo-lar amount (1:1) dissolving in ethanol. Three drops of glacial aceticacid were added as catalyst. The prepared material was taken in around bottom flask and refluxed for 8 h. The yield material wasSchiff base compounds containing imine groups (AHC@NA). Thenthe reaction mixture was allowed to cool to room temperature andsalt formation occurred at the bottom of the flask as light yellowmicrocrystalline powder. Using thin layer chromatography (TLC)the product was confirmed as a single compound and the solidproduct was separated using Whatman filter paper by filteringthe solution and kept for dryness (yield about 77%). Purity of thesynthesized compound was further increased by three timesrecrystallization in the solvent acetone and the reaction mecha-nism is shown in scheme below (see Scheme 1).

Crystal growth

The purified material was dissolved in the solvent acetone andstirred continuously for 5 h using magnetic stirrer and the pre-pared saturated solution was filtered and covered tightly with alu-minum foil kept undisturbed at room temperature for controlledslow evaporation. Natural evaporation of the acetone induces thespontaneous nucleation in the solution and tiny single crystals ofoptically transparent good quality have been harvested after7 days. Grown crystals were subjected to various characterizationstudies like XRD, NMR, FTIR, UV Visible, TG/DTA and SHG. (Supple-mentary Fig. S1) is shown the grown crystal of 2Cl4DBA.

N

H3C

H3C

C

O

H

N

H3C

H3C

C

N

H

C

Scheme 1. Reaction mec

Results and discussion

Single crystal X-ray diffraction

Single crystal data collection analysis was performed by usingdiffractometer-MACH3 from Enraf–Nonius and CCD detectorbased-SMART APEX from Bruker-Nonius Axs. The single crystalXRD study reveals that the crystal belongs to non-centrosymmetricorthorhombic system, satisfying one of the basic and essentialrequirements for the SHG activity of the material, the space group‘‘P212121’’ with the lattice parameter a = 7.6864 Å, b = 12.1654 Å,c = 13.9688 Å and V = 1306.138 Å, which is in good agreement withthose of reported values [4].

Powder X-ray diffraction

Powder X-ray diffraction patterns of finely crushed powder of2Cl4DBA crystal was scanned in the 2h values ranging from 10�to 80� and the powder X-ray diffraction pattern were recordedwith Bruker, D8 Advance model, Cu Ka radiation (k = 1.5406 Å).The powder XRD Prominent peaks of title crystal (hkl) values wereindexed using POWDER X software program and are shown inFig. 1.

1H and 13C NMR spectral analyses

In the present investigation, 1H and 13C NMR spectrum of thepurified 2C4DBA sample was recorded using Bruker 400 MHzinstrument in deuterated chloroform with tetramethylsilane(TMS) as the internal standard. The structure of 2Cl4DBA contain-ing different types of protons show different peaks as expected atdifferent chemical shift positions from the different environmentof the proton [5]. The protons in the aldehyde rings can see eachother as aligned (parallel) or opposed (anti-parallel) and come toresonance twice. The proton pairs are chemically equivalent by vir-tue of the symmetry within the molecule and have same electronicenvironment. Thus, proton in the aldehyde ring appears as doubletbecause their signals are indistinguishable, d (7.853, 7.831) ppmand d (6.774, 6.752) ppm gives two doublets respectively. Theimine protons (AHC@NA) have no neighbor proton and it should

NH 2

Cl

l

Add 3drops of Glacial acetic acid and reflux for 8hours

H2O

hanism of 2Cl4DBA.

Fig. 1. Powder XRD pattern of the grown crystal.

R.K. Balachandar, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 143–147 145

appear as a singlet. The singlet signal at d 8.261 ppm correspondsto the proton of imine group which confirms the formation ofthe Schiff base compound [6]. The d values for the protons of(ACH3)2 group attached to-N-Aromatic radicals are expected at3.082 ppm. The singlet signal at d 3.082 ppm denotes protons ofmethyl group. Aniline ring had four protons, out of the four protonstwo of hydrogen atoms were neighbors to two H-atoms thus itforms a two triplets (d 7.125, 7.283 ppm) and the remaining twoproton forms a doublets with each one H atom as neighbor (d7.056, 7.452 ppm) this is due to the chlorine atom is attached tothe ortho position of the aromatic aniline ring. 1H NMR spectrumof the grown material is shown in (Supplementary Fig. S2).

From 13C NMR of the title compound, the assignment of theeach signal to a unique carbon environment in the molecule is alsoidentified. Each carbon atom at different positions produces a dif-ferent signal. The shift (d 161.591) is due to the imine group carbonatom which confirms the formation of the Schiff base compound.The signal (d 40.170) is due to the methyl carbon atom and the

Fig. 2. FTIR spectrum of

three-line signal (d 76–77) from the CDCl3 solvent corresponds tothe single carbon atom; it appears as a triplet because of an inter-action with the deuterium atom. Rest of all the peaks correspondsto the aromatic carbons which fall on the aromatic region from (d111.035–152.814). Thus the molecular structure of the titlecompound is confirmed from the proton NMR and carbon NMRspectrum. 13C NMR spectrum of title material is shown in (Supple-mentary Fig. S3).

FTIR spectral analysis

FTIR spectrum was recorded for the crushed powder of the crys-tal using Shimadzu FTIR spectrophotometer. The spectra were re-corded by KBr pellet technique between the range 400 cm�1 and4000 cm�1 shown in Fig. 2. Benzylidene anilines display theirC@N stretching as a band at 1600 cm�1. The band obtained at1598 cm�1 is a proof for the formation of imine group (C = N) asa result of the condensation reaction between aldehyde and amine[7]. The expected bending vibrations of CAX bond are strong forCACl stretching is 600–800 cm�1. In the present case, the absorp-tion is noticed at 759 cm�1.

C-H stretching absorptions are weak absorptions expectedaround 2924 cm�1. C@C stretching absorption is confirmed fromthe band at 1502 cm�1. An out-of-plane CAH deformation bandis a characteristic of aromatic ring with ortho-di-substitution. Itis confirmed from the band at 750 cm�1. It is evidenced from theCAH deformation vibration at 750 cm�1 [8]. Absence of character-istic aldehyde bands at 2720 cm�1 and 2820 cm�1 indicates thatthere is no aldehyde group in the final product. FTIR spectrum doesnot show any signal corresponding to aldehyde group present inthe reactants. From the above observations the presence of thespecific groups are confirmed.

UV–visible spectral analysis

The optical absorption spectrum of the grown crystal wasrecorded using Elico SL218 Double beam UV–visible spectropho-

the grown crystal.

Fig. 3. UV–visible absorbance spectrum of the grown crystal.

146 R.K. Balachandar, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 143–147

tometer in the wavelength range of 190–1100 nm at room temper-ature. A sample of 1.7 mm thickness was used for measurementwithout polishing the crystal surface. The recorded UV–visiblespectrum is shown in Fig. 3. It is observed that cut off wavelengthis at 434 nm. The crystal has low absorption starts in the visibleand completely in the NIR region. The low absorbance in the regionfrom 434 nm to 1100 nm enables very good optical transmission ofthe second harmonic frequencies of Nd:YAG laser.

Thermal analysis

The thermal stability of the grown crystal was measured bythermo gravimetric analysis (TGA) and Differential thermal analy-sis (DTA) simultaneously from room temperature to 500 �C at theheating rate of 10 K/min, under nitrogen atmosphere using Net-zsch STA 409 PL Luxx as shown in Fig. 4. From TG analysis it is

Fig. 4. TG/DTA curve of the grown crystal.

observed that the material is stable up to 234 �C and weight lossof the material starts on further heating the sample. 85% of hugeweight loss is observed between the temperature 234oC and317oC due to the decomposition of the imine molecule and remain-ing 15% as carbon residue which is present in the material. Fromthe above observation, it is clear that there is no weight loss be-tween 100 �C and 200 �C which attributes that there is no inclusionof water molecules present in the crystal lattice and also no weightloss before the melting point, which indicates that the material ismoisture-free and stable up to 234 �C. From the DTA analysis thetwo sharp endothermic peaks were observed at 135 �C and321 �C, the first one corresponds to the melting point of the mate-rial, sharpness indicates the good crystalline nature and purity ofthe synthesized material and the second is corresponds to the com-plete decomposition of title compound which may release volatilegases present in the material [9]. Other than the solid–liquid trans-formation from the melting point onwards, no other phase trans-formations are noticed in the DTA curve.

Second harmonic generation measurement

SHG conversion efficiency measurement was carried out usingKurtz and Perry technique [10]. A Q-switched Nd:YAG laser beamof wavelength 1064 nm with input beam energy 3.8 mJ/pulse andpulse width 10 ns with a repetition rate of 10 Hz was used. Thegrown single crystal was powdered with a uniform particle sizeand tightly packed in a micro-capillary of uniform bore and ex-posed to the laser radiation. The bright green light emission(k = 532 nm) was observed which indicates the SHG behavior ofthe title material. The relative SHG efficiency of the title crystal(42 mV) is nearly 4.2 and 1.54 times that of KDP (10 mV) and urea(27.2 mV) respectively.

Conclusion

The organic NLO material 2-chloro-N-[4-(dimethylamino)ben-zylidene]aniline was successfully synthesized and grown the singlecrystal from the acetone by restricted slow evaporation technique.Single crystal X-ray diffraction has been carried out to find the unitcell parameter and the crystalline nature of the synthesized mate-rial was analyzed by powder XRD pattern. Confirmation of themolecular and structural was done by FTIR and NMR spectralanalysis. UV visible spectrum of the grown crystal shows lowabsorbance with cutoff 434 nm in the near visible region and entirenear IR region. A thermal property of the grown material studiedby TG/DTA analysis and melting point of the material was foundto be 135 �C and the materials was stable up to 235 �C. The SHGrelative efficiency was found to be more efficiency 4.2 times and1.5 times than that of standard KDP and urea as a reference mate-rial. Thus the characterization confirms the suitability of the growncrystal for NLO applications.

Acknowledgements

The authors express thank to R. Lakshmi sundaram, Sri Ramach-andra University for helping in the NMR spectral analysis. Theauthors also express thanks to VIT University for their constantencouragement and financial support.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.saa.2013.07.021.

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