Synthesis, growth, optical, thermal and nonlinear optical studies of dimethylammonium picrate single crystal

Synthesis, growth, optical, thermal and nonlinear optical studies of dimethylammonium picrate single crystal

G Model ARTICLE IN PRESS IJLEO 56518 1–4 Optik xxx (2015) xxx–xxx Contents lists available at ScienceDirect Optik journal homepage: www.elsevier...

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G Model

ARTICLE IN PRESS

IJLEO 56518 1–4

Optik xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

Optik journal homepage: www.elsevier.de/ijleo

Synthesis, growth, optical, thermal and nonlinear optical studies of dimethylammonium picrate single crystal

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K. Syed Suresh Babu a,b , G. Peramaiyan c , M. NizamMohideen b , M. Dhavamurthy a , R. Mohan a,∗ a

Department of Physics, Presidency College (Autonomous), Chennai 600 005, India Department of Physics, The New College (Autonomous), Chennai 600 014, India c Department of Physics, Vel Tech University, Avadi, Chennai 600 062, India b

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Article history: Received 24 December 2014 Accepted 11 October 2015 Available online xxx

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Keywords: Crystal structure Organic compounds Nonlinear optical material Optical properties

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1. Introduction

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Dimethylammonium picrate (DMAP) was synthesized from dimethylformamide and picric acid as precursors and crystals were grown by the slow evaporation solution growth technique. Single crystal X-ray diffraction study revealed that DMAP crystallizes in orthorhombic system with space group Pca21 . UV–Vis–NIR spectral study showed percentage of transmittance about 55% with a lower cut-off wavelength 475 nm. The relative second harmonic generation efficiency of grown crystal was found to be 3.1 times of KDP by Kurtz and Perry technique. From the TG–DT analyses, it is observed that the melting point is observed at 161.8 ◦ C. The laser damage density of DMAP crystal was found to be 1.9 GW/cm2 for 1064 nm Nd:YAG laser radiation. © 2015 Published by Elsevier GmbH.

Organic molecular compounds with a high degree of delocalized ␲-electrons have received a great deal of attention due to their more favorable nonlinear response [1–3]. Picric acid is known to have delocalized ␲-conjugation system and forms crystalline complex with organic and inorganic compounds. In the complex formation with picric acid, deprotonation of phenolic OH group facilitates hydrogen bonding interaction between picric acid and other molecules. Recently, picrate complexes have attracted material scientists due to their high second order nonlinear optical response [4–6]. Dimethylammonium picrate (DMAP) was synthesized using dimethylamine and picric acid as precursors and it crystallizes in orthorhombic system with space group Pca21 with ˚ b = 11.119 (8) A, ˚ c = 21.326 the lattice parameters: a = 9.995 (3) A, (7) A˚ and ˛ =  = ˇ = 90◦ . Refinement of the crystal structure was carried out by the full-matrix least-squares method and the R value was 0.0542 [7]. Recently, the crystal growth, thermal stability (melting point: 158 ◦ C), laser damage threshold (0.34 GW/cm2 ) and the second harmonic generation efficiency (2 times of KDP) of DMAP have been reported [8,9]. In the present investigation,

∗ Corresponding author at: Department of Physics, Presidency College, Chennai 600 005, India. Tel.: +91 9444455983; fax: +91 44 2235 2870. E-mail addresses: [email protected] (K. Syed Suresh Babu), [email protected] (R. Mohan).

Fig. 1. Reaction scheme of DMAP.

Dimethylammonium picrate (DMAP) was synthesized using N,Ndimethylmethanamide and picric acid as precursors. It is observed that DMAP crystal has good optical, thermal and laser damage threshold properties compared to already reported one.

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2. Experimental

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2.1. Synthesis and crystal growth

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In the present work, the commercially available analytical grade dimethylformamide (DMF) and picric acid (Merck, 99%) was used for synthesis of dimethylammonium picrate. A mixture of acetone and distilled water (1:1) was used as a solvent. The purity of the synthesized salt was further improved by recrystallization process. The reaction scheme of DMAP is shown in Fig. 1. The prepared solution was allowed to evaporate at room temperature. After a period of 16 days well-defined, transparent, good morphological crystals were harvested. The average size of the grown crystal is 12 mm × 4 mm × 3 mm as shown in Fig. 2.

http://dx.doi.org/10.1016/j.ijleo.2015.10.058 0030-4026/© 2015 Published by Elsevier GmbH.

Please cite this article in press as: K. Syed Suresh Babu, et al., Synthesis, growth, optical, thermal and nonlinear optical studies of dimethylammonium picrate single crystal, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.10.058

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Fig. 2. Photograph of the grown DMAP crystal.

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3. Results and discussion

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3.1. Single crystal X-ray diffraction analysis

In order to confirm the complex formation of DMAP, the intensity data were collected for a synthesized DMAP crystal using a Bruker kappa APEXII single crystal X-ray diffractometer with 62 ˚ at 293 K graphite monochromatic MoK␣ radiation ( = 0.71073 A) 63 [10]. The structure was solved by the direct method and refined by 64 the full matrix least-squares technique on F2 employing the SHELXL 65 97 program package [11]. Crystallographic data for structure anal66 yses of the title compound are listed in Table 1. The asymmetric 67 unit of the title compound comprises of a N-methylmethanamine 68 cation and picrate anion (Fig. 3). The crystal structure of DMAP 69 along the crystallographic ‘c’ axis is depicted in Fig. 3. The chemical 70 composition of the crystal is C6 H2 N3 O7 , C2 H8 N (DMAP). DMAP 71 compound crystallizes in orthorhombic crystal system with space 72 ˚ b = 21.3323 group Pca21 . The cell parameters are a = 9.9960 (5) A, 73 (12) Å, c = 11.1012 (6) A˚ and volume V = 2367.2 (2) A˚ 3 . The lattice 74 parameters for dimethylammonium picrate are comparable with 75 the values reported in the literature. The N-methylmethanamine 76 molecule exists as N-methylmethanaminium ion due to the proto77 78Q2 nation at the nitrogen atom (Fig. 4). The picrate anions adopt the keto form with C1 O1 and C7 O8 bond distance of 1.248 (3) and 79 1.250 (3) A, C1 C2, C1 C6, C7 C8 and C7 C12 bond distance of 80 1.441 (5), 1.451 (5), 1.451 (4) and 1.447 (4) A, respectively, which 81 is longer than the other C C bond lengths (between 1.374 (5) 82 and 1.460 (4) A) in the benzene ring. The bond angles C2 C1 C6 83 and C8 C7 C12 is 112.0 (3) and 111.0 (2)◦ , respectively, which 84 is the case in some picrate complexes, while the corresponding 85 60 61

Table 1 Crystal data and structure refinement for DMAP. Empirical formula Formula weight Temperature Wavelength Crystal system, space group Unit cell dimensions Volume Z, Calculated density Absorption coefficient F (0 0 0) Crystal size Theta range for data collection Limiting indices Reflections collected/unique Completeness to theta = 25.76 Max. and min. transmission Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2sigma (I)] R indices (all data) Absolute structure parameter Largest diff. peak and hole

C8 H10 N4 O7 274.20 293 (2) K 0.71073 A˚

Fig. 3. Morphology of DMAP crystal.

bond angle of picric acid is 116.4 (5)◦ [12]. In the picrate anion the deprotonated phenolate oxygen atom deviates slightly from the plane of the benzene ring (torsion angle O3 C1 C6 C5 = −175.8 (3)◦ and O8 C7 C12 C11 = 176.4 (3)◦ ). The twist angles between the benzene rings (C1 C6 and C7 C12) and the ortho nitro groups (N1, N3, N4 and N6) are 22.6 (2), 4.5 (2), 5.5 (2) and 19.6 (2), respectively. The para positioned nitro groups are twisted by 1.6 (2)◦ (N2) and 4.2 (2)◦ (N5). The picrate ions are stacked headto-tail, presumably as a result of charge-transfer interactions. In the crystal the cation and the picrate anions of crystallization are involved in N H· · ·O and week C H· · ·O interactions, to form a three-dimensional supramolecular network (Table 2). The nitro group of the picrate anion interacts with N-methylmethanamine cation via a pair of bifurcated N H· · ·O [N(7) H(7A)· · ·O(1), N(7) H(7B)· · ·O(8), N(7) H(7B)· · ·O(13), N(7) H(7A)· · ·O(2), N(8) H(8A)· · ·O(1), N(8) H(8A)· · ·O(1), N(8) H(8B)· · ·O(8) and N(8) H(8B)· · ·O(9)] hydrogen bonds, forming a hydrogen bonded ring motif with graph-set notation R12 (6) [13] and these motifs form a ring R22 (8). The knowledge of morphology of crystal helps to grow the crystals in a required direction for device fabrication. The morphology of DMAP with ten well developed facets is shown in Fig. 5. It is observed that the growth rate is faster along b-axis than a and c-axes of the crystal. 3.2. Linear and nonlinear optical studies Optical transmittance is an important parameter for NLO materials. UV–Vis–NIR spectrum of DMAP was recorded using a Varian Cary 5E spectrometer in the range 200 nm–800 nm as shown in Fig. 6. Single crystal of thickness about 1.6 mm was used for this

Orthorhombic, Pca21 ˚ b = 21.3323 (12) A; ˚ a = 9.9960 (5) A; c = 11.1012 (6) A˚ 2367.2 (2) A˚ 3 8, 1.539 Mg/m3 0.137 mm−1 1136 0.35 mm × 0.30 mm × 0.25 mm 2.25–25.76◦ −8 ≤ h ≤ 12, −21 ≤ k ≤ 26, −13 ≤ l ≤ 13 12,050/4177 [R(int) = 0.0265] 99.6% 0.9667 and 0.9038 Full-matrix least-squares on F2 4177/5/363 1.029 R1 = 0.0435, wR2 = 0.1077 R1 = 0.0564, wR2 = 0.1175 −0.3 (15) 0.261 and −0.228 e. A˚ −3

Fig. 4. Molecular configuration and atom numbering scheme for the title compound. Displacement ellipsoids are drawn at the 50% probability level.

Please cite this article in press as: K. Syed Suresh Babu, et al., Synthesis, growth, optical, thermal and nonlinear optical studies of dimethylammonium picrate single crystal, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.10.058

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Table 2 Hydrogen bonds for DMAP. D H· · ·A N(8) N(8) N(8) N(8) N(7) N(7) N(7) N(7)

H(8A)· · ·O(1) H(8A)· · ·O(7) H(8B)· · ·O(8) H(8B)· · ·O(9) H(7A)· · ·O(1) H(7A)· · ·O(2) H(7B)· · ·O(8) H(7B)· · ·O(13)

d(D H) (Å)

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0.922 (10) 0.922 (10) 0.925 (10) 0.925 (10) 0.925 (10) 0.925 (10) 0.930 (10) 0.930 (10)

1.872 (15) 2.39 (3) 2.09 (3) 2.12 (2) 1.95 (2) 2.36 (3) 2.01 (2) 2.24 (4)

2.756 (3) 2.985 (5) 2.860 (3) 2.897 (4) 2.767 (3) 3.089 (4) 2.889 (3) 2.856 (3)

160 (3) 122 (2) 140 (3) 141 (3) 147 (3) 136 (3) 158 (4) 123 (3)

of 10 ns with the repetition rate 10 Hz was used. The DMAP and KDP crystals were ground to a uniform particle of sizes about 55, 150 and 250 and 400 ␮m and then packed in capillary tubes. The second harmonic generation (SHG) was confirmed from the emission of green radiation ( = 532 nm) from the samples. The intensity of the green light was measured using a photomultiplier tube. It is observed that the SHG signal voltage increases with increasing particle size up to 250 ␮m and attains saturation above 250 ␮m. It shows a strong NLO behavior of DMAP crystal. The SHG signal voltage of the grown crystal was found to be 58.28 mV while KDP crystal gave a signal of 18.8 mV for the same input energy. The relative SHG efficiency of grown crystal was found to be 3.1 times of KDP. 3.3. Thermal analyses

Fig. 5. Packing diagram of the title compound viewed down the c axis. Dashed lines indicate intermolecular strong N H· · ·O weak C H· · ·O hydrogen bonds.

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study. From the spectrum, it is evident that DMAP crystal has enough percentage of transmittance about 55% with a lower cutoff wavelength 475 nm which is sufficient for frequency conversion from 1064 nm laser radiation. The relative second harmonic generation efficiency of DMAP was measured by employing a Kurtz and Perry powder technique [14]. A Q-switched Nd:YAG laser beam of wavelength 1064 nm with an input power of 8.5 mJ, pulse width 60

3.4. Laser damage threshold study The laser damage density of DMAP crystal was measured using a Nd:YAG laser with the wavelength of 1064 nm. A fundamental wavelength, 1064 nm, with a pulse width of 10 ns and a repetition rate of 10 Hz was used. The laser beam of diameter 2 mm was focused on the crystal. The sample was placed at the focus of a plano-convex lens of focal length 30 cm. The

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Thermal stability ensures the suitability of material for possible NLO application up to the melting point. Thermogravimetric and differential thermal analyses (TGA/DTA) and differential scanning calorimetry (DSC) analysis have been carried out using a SDT Q 600 V20.9 Build 20 analyzer. The thermal analyses were carried out in a nitrogen atmosphere with a heating rate of 10 ◦ C/min from 20 ◦ C to 800 ◦ C. The TGA/DTA curve is shown in Fig. 7. From the DTA curve, it is observed that the melting point is observed at 161.8 ◦ C. and a sharp peak at 272.88 ◦ C corresponds to the decomposition point of the material. The melting and decomposition temperatures of DMAP compound are further confirmed from the DSC curve as shown in Fig. 8.

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Wavelength (nm) Fig. 6. UV–visible transmittance spectrum of DMAP.

Fig. 7. TGA–DTA curve of DMAP.

Please cite this article in press as: K. Syed Suresh Babu, et al., Synthesis, growth, optical, thermal and nonlinear optical studies of dimethylammonium picrate single crystal, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.10.058

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thermal stability make this crystal suitable for SHG and optoelectronic applications.

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Acknowledgment

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One of the authors K.S.S.B. is thankful to SAIF, IIT Madras, for X-ray diffraction data collection and characterization studies.

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References

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surface damage threshold of the crystal was calculated using the expression (Pd ) = E/r2 where E is the input energy (mJ),  is the pulse width (ns) and r is the radius of the spot (mm). The laser damage density of DMAP crystal was found to be 1.9 GW/cm2 . 4. Conclusions Dimethylammonium picrate was synthesized from DMF and picric acid as precursors and crystals were grown by the slow evaporation technique. The crystal structure of the compound was elucidated by single crystal X-ray diffraction study. The optical transmittance study reveals transparency of the crystal with a cutoff of 475 nm. The relative SHG efficiency is found to be 3.1 times of KDP. The TGA–DTA and DSC analyses show the melting point of DMAP at 161 ◦ C. The optical damage density of DMAP crystal was found to be 1.9 GW/cm2 . The high nonlinearity, transparency and

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