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Optik 125 (2014) 333– 337

Contents lists available at ScienceDirect

Optik

jou rn al homepage: www.elsev ier .de / i j leo

phase matchable nonlinear optical crystal salicylideneaniline:ynthesis, growth and characterization

. Anbarasu, Prem Anand Devarajan ∗

epartment of Physics, St. Xavier’s College (Autonomous), Palayamkottai 627 002, Tamilnadu, India

r t i c l e i n f o

rticle history:eceived 9 February 2013ccepted 22 June 2013

eywords:alicylideneaniline (SAN)

a b s t r a c t

A new NLO organic crystal of salicylideneaniline (SAN) was synthesized and SAN bulk crystal was grownalong <412> plane using uniaxial crystal growth method of Sankaranarayanan–Ramasamy with a newmodification in the growth assembly. The crystal was grown with a growth rate of 2 mm/day upto adimension of 4 cm in length and 6 cm in diameter having a cylindrical morphology within 30 days.The powder XRD analysis confirmed the crystalline perfection. The presence of C N bond with intra-molecular hydrogen bonding on the protonation of ions were confirmed by FTIR analysis. The range

1 13

-ray powder diffractionV–vis–NIRielectric studieshase matching

of optical absorbance was ascertained by recording UV–vis–NIR spectrum. The 1H and C NMR spec-trum confirms the molecular structure. Dielectric studies were carried out to estimate the dielectricparameters of the grown crystal in the frequency range from 100 Hz to 100 KHz. The existence of secondharmonic generation (SHG) signal was observed using Nd:YAG laser with the fundamental wavelength of1064 nm. Phase matching parameters of the grown crystal confirms that salicylideneaniline is a promisingcandidate for LASER applications.

. Introduction

Extensive studies were made on the synthesis and crys-al growth of nonlinear optical (NLO) materials over the pastecade because of their potential applications in the field ofelecommunication, optical processing and optical switching, har-

onic generation, phase modulation, switching and other signalrocessing devices [1–3]. Hence, organic materials are of particular

nterest because the NLO responses in this broad class of materialsre microscopic in origin offering an opportunity to use theo-etical modeling coupled with synthetic flexibility to design androduce novel materials [4,5]. The second order nonlinear opticalaterials, a lot organic compounds with polarized �-conjugation

ystems have succeeding inorganic compounds [6,7]. Organic non-inear optical crystals have good nonlinear optical susceptibilitiesnd low damage threshold values in comparison with inorganicounterparts. In order to satisfy the day to day technologicalequirements, new nonlinear optical materials are mandatory toatisfy the requirements. There are many works carried out toesign the new organic crystals with large second order opti-

al nonlinearities [8–17]. Recently the authors have synthesized,rown and characterized a series of imine based organic NLO crys-als for photonics device fabrication [18]. In this letter, we report the

∗ Corresponding author.E-mail address: devarajanpremanand@gmail.com (P.A. Devarajan).

030-4026/$ – see front matter © 2013 Elsevier GmbH. All rights reserved.ttp://dx.doi.org/10.1016/j.ijleo.2013.06.041

© 2013 Elsevier GmbH. All rights reserved.

synthesis of a new “push-pull” Schiff base salicylideneaniline (SAN)that promotes the chiral packing in the solid state. This propertywas exploited to grow organic nonlinear crystals showing secondharmonic generation efficiency 4 times larger than that of ureaand 26 times larger than that of KDP in IR wavelength of 1906 nm.The synthesized and as grown crystals of salicylideneaniline werecharacterized by single crystal X-ray diffraction (XRD), X-ray pow-der diffraction (XRPD), Fourier transform infrared (FTIR), ultraviolet– visible – near infrared (UV–vis–NIR), 1H1 and C13 NMR spectro-scopic analyses, Dielectric studies and SHG test so as to improvisethis material for photonics device fabrication.

2. Experimental techniques

2.1. Chemicals

Salicylaldehyde (99% pure AR grade) and Aniline (99.5% pure ARgrade) were purchased from E-merck Co. Ltd.

2.2. Synthesis of salicylideneaniline

SAN was prepared using the typical synthetic method for iminederivatives [19]. A solution of aniline was taken in a 250 mL Borosil

glass beaker. Salicylaldehyde was added five portions to the solu-tion containing aniline and strongly agitated using a magneticstirrer for three hours. After 3 h, salicylideneaniline was formed as acrystalline salt with water as a by-product. The crystalline salt was

334 S. Anbarasu, P.A. Devarajan / Optik 125 (2014) 333– 337

pT

2

cbpwtsrwpAwwstwoTfits

2

sphtgte

Fig. 1. Reaction scheme of salicylideneaniline.

urified by repeated process in N,N-dimethyl formamide (DMF).he reaction scheme is shown in Fig. 1.

.3. Solubility study

The synthesized salt was used to measure the solubility of SANrystals in N,N-Dimethyl formamide (DMF). A 250 ml borosil glasseaker filled with 100 ml DMF was placed inside a constant tem-erature bath. An acrylic sheet with a circular hole at the middleas placed over the beaker through which a spindle from an elec-

ric motor, placed on the top of the sheet was introduced into theolution. A Teflon paddle was attached at the end of the rod for stir-ing the solution. The synthesized salt was added in small amountsith DMF solvent and stirring was continued till the formation ofrecipitate, which confirmed the supersaturation of the solution.

20 ml of the saturated solution was withdrawn by means of aarmed pipette and the same was poured into a clean, dry andeighed Petri dish. The solution was kept in a heating mantle for

low evaporation till the whole of the solution got evaporated andhe mass of the SAN salt in 20 ml of solution was determined byeighing Petri dish with salt and hence the solubility, i.e. quantity

f salt in gram dissolved in 100 ml of the solvent was determined.he solubility of SAN crystals in DMF solvent was determined forve different temperatures (30, 35, 40, 45 and 50 ◦C) by adoptinghe same procedure. The resulting solubility curve of pure SAN ishown in Fig. 2.

.4. Crystal growth technique

Recrystallized salt of SAN was used to prepare saturatedolutions with DMF as solvent. By slow evaporation at room tem-erature seed crystals of dimension 2 mm × 1.5 mm × 3 mm werearvested in a period of 25–30 days. Fig. 3 shows SAN single crys-als grown by slow solvent evaporation technique. Defect free and

ood optical quality seed crystal was selected to grow bulk crys-al by modified Sankaranarayanan–Ramasamy apparatus reportedlsewhere [18]. Fig. 4 shows an unidirectional SAN single crystal of

30 35 40 45 50

20

30

40

50

60

70

Sol

ubili

ty (g

/10m

l)

Tempe rature (oC)

Fig. 2. Solubility curve of SAN NLO crystal.

Fig. 3. Photograph of as grown crystal of SAN NLO crystal by slow evaporationmethod.

6 cm in diameter and 4 cm in thickness was successfully grown bySankaranarayanan–Ramasamy method.

2.5. Growth rate of SAN crystal

It is well known that the evaporation rate of the solvent dimethylformamide (DMF) into the atmosphere is a function of temperature,humidity and air velocity. It is evident that the evaporation processin the atmosphere is diffusion of DMF molecules coming out of itssurface through the air larger covering its surface. To calculate theo-retically the absolute evaporation rate, we must know the diffusioncoefficient of DMF vapour in air and the thickness of the boundarylayer accurately. Kazuo Histake et al. reported a detailed surveyon the evaporation rate [20]. A reaction for the growth rate of SRmethod is given by RT = 0.318K (SE)/r2d (cm per day), where K is theproportionality constant, S is the solubility of the material (g/ml) ofthe solvent, E is the evaporation rate of the solvent (ml per day), r isthe radius of the vessel, d is the density of the material (g/cm3) andT is the temperature (K). By using the above parameters, the growthrate of the crystal is calculated. The evaporation rate of the solventin an ampoule was also measured by observing the lowering rateof the top surface of the solution level.

3. Results and discussion

3.1. Single crystal XRD

The single crystal XRD diffraction was carried out using asingle crystal X-ray diffractometer (Model; Brucker-Nonius Kappa Apex II CCD). From the data, we found that SAN crystalretained its orthorhombic crystal structure with lattice dimensionsa = 27.971 A, b = 5.939 A, c = 12.879 A and = 90◦, = 90◦, � = 90◦ and

V = 2139 A3 with non-centro symmetric space group Fd2d. [21].

Fig. 4. Photograph of as grown SAN NLO crystal by Sankaranarayanan–Ramasamymethod.

S. Anbarasu, P.A. Devarajan / Optik 125 (2014) 333– 337 335

10 20 30 40 50 60 70 800

2000

4000

6000

8000

10000

12000

14000

16000

18000

(022

)

(020

)

(412

)

(410

)(3

11)

(111

)Inte

nsity

Angle (2 )

Fig. 5. XRPD spectrum of SAN NLO crystal.

4000 350 0 300 0 250 0 200 0 150 0 100 0 50 0

0

20

40

60

80

100

%T

-1

3

rCwcXtw

3

eloa4bn3ioa

TF

200 30 0 40 0 50 0 60 0 70 0 80 0 90 0 100 0 110 0 120 0-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

325

257

% A

wavelength (nm)

concordant with the values reported by Ogawa et al. [29].

wavenu mbe r (cm )

Fig. 6. FTIR Spectrum of SAN NLO crystal.

.2. X-ray powder diffraction (XRPD) studies

The powder sample of SAN crystal was subjected to powder X-ay diffraction studies with Riech Single X-ray diffractometer usinguK� radiation of wavelength � = 1.5418 A over the range of 10–60◦

ith a scan speed of 0.2◦/s. Fig. 5 shows the XRPD spectrum of SANrystal. The peaks were indexed using X-Pert software. The powder-ray Diffraction experiment showed that the synthesized salt and

he grown crystals were of the single phase of salicylideneanilineith good crystalline perfection.

.3. FTIR analysis

The FTIR spectrum was recorded in the range 400–4000 cm−1

mploying Brukker model IFS 66 V FTIR spectrometer by KBr pel-et technique. Fig. 6 shows the FTIR spectrum of SAN crystal. Forrganic molecule, the FTIR region is divided into fractional groupnd fingerprint region. The fractional group region extends from000 cm−1 to 1300 cm−1 where as the finger print region liesetween 1340 cm−1 to 900 cm−1. The spectrum shows a strong phe-olic region at 3650 cm−1 to 3584 cm−1. A broad peak centered at

−1

401 cm is due to the O H stretching mode. The in-plane bend-ng mode of OH group in SAN is assigned at 1223 cm−1. The O Hut of plane bending mode is at 822 cm−1. The weak band observedt 3250 cm−1 is attributed to the N H stretching of SAN molecule

able 1T-IR data of SAN crystal.

Wavenumber (cm−1) Assignments

1430–1650 C C stretching1625–1575 C C heavy doublet stretching1454 C C skeletal vibration1677 C N imine stretching1000 C C C in-plane bending736, 691, 657, 569 547,521,492 C C C out of plane bending

Fig. 7. UV–vis–NIR Spectrum of SAN NLO crystal.

[22,23]. The FTIR bands at 3054, 3024 and 2980 cm−1 are due toC H stretching vibration of imine [24–26]. The vibration due toC H in-plane bending and out of plane bending can be visualizedfrom the bands occurring at 1320, 1274, 1185, 1169, 1149, 1073 and1030 cm−1 and 979, 943, 917, 896, 865 and 840 cm−1 respectivelywhich is in good agreement with the literature reported [22]. Theother observed FTIR wavenumbers are tabulated in Table 1. Thusthe FTIR spectrum confirms the various functional groups in theSAN molecule.

Thus the absorption peaks characterizing the various functionalgroups are in very good agreement with those reported in litera-ture.

3.4. UV–vis–NIR studies

The optical absorption spectra of SAN crystals were recorded inthe range 200–1200 nm using Varian Carry 5E spectrometer. Fig. 7shows the UV–vis–NIR spectrum recorded with highly transparentsingle crystal of SAN of thickness 2 mm. It is seen from the absorp-tion spectrum that the crystal is transparent in the entire rangeof 300–1200 nm without any absorption peak which is an essen-tial parameter for NLO crystals. It is further observed that the UVcut off of SAN is below 325 nm making the application in the blueregion easier with laser. The presence of an absorption peak cen-tered at 250 nm confirm the structure of imine [27–29]. It is also in

Fig. 8. 1H1 NMR spectrum of SAN NLO crystal.

336 S. Anbarasu, P.A. Devarajan / Optik 125 (2014) 333– 337

3

tcwpshtappFttbibta

3

sfiDst

Fig. 9. C13 NMR spectrum of SAN NLO crystal.

.5. 1H1 and C13 NMR analyses

The NMR spectrum was recorded using a Brukker ARX 300 spec-rometer in CDCl3 at 23 ◦C. Fig. 8 shows 1H1 NMR spectrum of SANrystal. The powder sample of SAN was dissolved in dieurated waterith CDCl3 as internal standard. The chemical shift values of theroton were plotted and the 1H1 NMR spectrum of the compoundhows a singlet at 13.2 ppm which corresponds to the proton of theydroxyl group. The resonance at 8.59 ppm is assignable to a pro-on of the imine carbon. The multiplet surrounded at 6.9–7.43 ppmre attributed to aromatic protons. Since the spectrum has no othereaks, the crystal was recorded as a pure. The structure of the com-ound was further supported by C13 NMR spectrum as shown inig. 9. The resonance at 161.19 ppm is pertained to the carbon ofhe benzene ring with the hydroxy group substituted. Additionallyhe signals raising at 117–133 ppm is due to the aromatic ring car-ons. The peak at 162.71 ppm is ascertained to the carbon of the

mine moiety. The signal at 148.5 is pertained to the carbon of theenzene ring attached to the nitrogen in the imine moiety. Thushe molecular structure is confirmed by 1H1 and C13 NMR spectralnalyses.

.6. Dielectric studies

In order to carry out the dielectric measurements, carefullyelected sample of SAN were cut and later polished using paraf-

n oil and fine grade alumina powder to obtain good surface finish.ielectric permittivity measurements were carried out with the

ilver coated sample placed inside a dielectric cell kept at roomemperature in the frequency range 50 Hz to 5 MHz using Hioki

Fig. 10. Dielectric Constant of SAN NLO crystal.

Fig. 11. Dielectric Loss of SAN NLO crystal.

3532-50 LCR Hitester at various temperatures ranging from 40 to70 ◦C in steps of 10 ◦C. The dielectric constant (εr was calculatedusing the relation ε = εr D where D is the dissipation factor. Fig. 10shows the dielectric constant and dielectric loss at different tem-peratures. From the graph (Fig. 11) it is evident that SAN denied toconduct lower frequency a.c signal, where as it will stronger beyond100 KHz leads to the restriction of electric potential at higher fre-quencies. Similar trend is also observed for dielectric loss in whichas the frequency increases dielectric loss decreases. It is importantto note that as the temperature is increased the values of dielectricconstant for the corresponding frequencies are increased. At 50 Hzof 60 ◦C, the dielectric constant is found to be 1.5. Thus from thedielectric measurements it is clear that SAN is a potential candidatefor electro-optic application due to its low dissipation factor.

3.7. NLO test

The ratio of the harmonic and fundamental intensities gives theefficiency of the sample and it was calculated from the relation

dsample

dKDP=

[IsampleSH

IKDPSH

]1/2

×[

IKDPFW

isampleFW

]

Using the values of fundamental and second harmonic intensi-ties from the oscilloscope traces the measured SHG was comparedwith KDP and found that the as grown SAN single crystal hasnearly 26 times higher NLO efficiency than KDP, which us a familiarorganic NLO material. The fundamental wavelength emitted froma Q-switched Nd:YAG laser was used. A photodiode was used as

a reference to monitor the pulse fluctuations in the input beam.SAN sample was grinded using standard sieves in the range lessthan 106 �m to above 150 �m. The measurement of SHG outputfor various particle size show the increasing SHG intensities with

<10 6 106 -12 5 125 -15 0 150 <0

25

50

75

100

125

150

175

200

225

250

275

300

SHG

outpu

t (mV)

Particle Size (micr o meter)

Fig. 12. Phase matching curve of SAN NLO crystal.

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(diethylamino)-2-[(4-propylphenylimino)methyl]phenol: a combined exper-

S. Anbarasu, P.A. Devaraj

ncreasing particle size upto 150 �m as shown in Fig. 12, whichonfirm the phase matching behavior of the material. Hence SANrystal can be used as an efficient frequency doubler and opticalarametric oscillator provided if large size single crystal is grown.wing to its SHG efficiency, SHG is considered as a promising mate-

ial for Laser Damage Threshold of SAN was found to be 0.47 W/cm2.ased on this study, we could know that SAN is a promising phaseatchable NLO crystal for LASER generation.

. Conclusion

In the present study, single crystal of pure SAN was synthesized,rown and characterized using XRD, XRPD, FTIR, UV–vis–NIR, 1H1

C13 NMR, Dielectric studies and NLO test and Phase matchingnalyses. The cell parameters of the grown crystal were elucidatedhrough single crystal XRD. The functional groups of SAN singlerystal were identified using FTIR analysis. Optical absorption spec-rum confirms the SAN crystal exhibits nearly zero absorption in theange of 400–1100 nm. The molecular structure of SAN single crys-al was confirmed by 1H1 and C13 NMR analyses. From the dielectrictudies, it is evident that SAN single crystal has lesser defects. Owingo its SHG efficiency, SHG is considered as a promising material foraser Damage Threshold of SAN was found to be 0.47 W/cm2. Thehase matching analysis reveals the possibility of using SAN singlerystal for LASER generation.

cknowledgements

The authors would like to thank University Grants Commis-ion, Bahadurshah Zafar Marg, New Delhi – 110 002, India forunding this Major Research Project (File No.: 40-434/2011(SR), dt.4.07.2011). and Dr. M. Basheer Ahamed, The Head, Department ofhysics, Crescent Engineering College, Chennai – 600 048, India foresting SHG, using Q-switched Nd:Yag laser.

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