Synthesis, structural, thermal, mechanical, second harmonic generation efficiency and laser damage threshold studies of 4-dimethylaminopyridinium-3,5-dicarboxybenzoate trihydrate single crystal

Optical Materials 72 (2017) 247e256

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Synthesis, structural, thermal, mechanical, second harmonic generation efficiency and laser damage threshold studies of 4-dimethylaminopyridinium-3,5-dicarboxybenzoate trihydrate single crystal M. Rajkumar, M. Saravanabhavan, A. Chandramohan* Post-Graduate and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore, 641 020, Tamil Nadu, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 8 May 2017 Received in revised form 5 June 2017 Accepted 6 June 2017

4-dimethylaminopyridinium-3,5-dicarboxybenzoate trihydrate was synthesized and single crystals grown by slow solvent evaporation solution growth technique at ambient temperature. The single crystal XRD analysis was carried out to establish the molecular structure of the title crystal. Further, the data indicate that the title salt crystallizes in orthorhombic crystal system with the non-centrosymmetric space group, Pna21. The established molecular structure was further confirmed by 1H and 13C NMR spectroscopic studies. The grown crystal has been subjected to FT-IR spectral study to identify the various functional groups. The UVeViseNIR transmission spectrum was recorded on powdered sample of crystal to determine the lower wavelength cut-off and optical band gap. The photoluminescence spectrum was recorded to investigate the luminescence properties of the salt crystal. The thermal and mechanical stabilities of the crystal were established by TG/DTA analyses and Vickers microhardness study, respectively. The dielectric studies of the grown crystal were executed at different temperatures as a function of frequency to investigate its electrical properties. The SHG efficiency of the title crystal was investigated and its value is 0.89 times that of KDP crystal. The laser damage threshold value is found to be 1.06 GW/cm2. © 2017 Elsevier B.V. All rights reserved.

Keywords: Crystal growth Crystal structure Hydrogen bonding Photoluminescence SHG activity Laser damage threshold

1. Introduction Nowadays, considerable attention has been paid to the development of the nonlinear optical materials with extended nonlinearity and high molecular polarizability (b) because of their potential applications in the field of laser technology, optical telecommunication, image processing, optical computing, optical communication, opto-electrical switching, electro-optic modulation, Terahertz wave generation and data storage devices [1e4]. Unlike Inorganic crystals, organic NLO crystals with aromatic rings possess several advantages such as high non-linearity, high molecular polarizability, fast response, ease of device fabrication, molecular flexibility, low mobility, large band gap and high laser damage threshold [5,6]. Much emphasis is focused on the formation of stable salts as a

* Corresponding author. E-mail address: [email protected] (A. Chandramohan). http://dx.doi.org/10.1016/j.optmat.2017.06.011 0925-3467/© 2017 Elsevier B.V. All rights reserved.

method for the synthesis of new materials with different physicochemical properties through the use of supramolecular synthons [7,8]. Thus, salts can be synthesized with the intention to alter solid-state property of a molecule without affecting its intrinsic structure [9]. The nature of the constituent species and their relative orientations within the solid plays a crucial role in determining the physical and chemical properties of the organic molecular solids. Organic molecules containing p electron conjugated systems asymmetrized by the electron donor and acceptor groups are highly polarizable entities for NLO applications [10]. Hydrogen bonding is one of the important types of non-covalent bond interactions which plays an important role in chemical and crystal engineering, as well as in supramolecular chemistry and helps to create non-centrosymmetric structures of crystals [11e14]. Noncentrosymmetric structure is an essential requirement for material to exhibit second harmonic generation [15]. Moreover, hydrogen bonding also enhances the mechanical and thermal stability of the crystal [16,17]. The hydrogen bonding between

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carboxylic acids and heterocyclic nitrogen atoms is utilized to generate supramolecular assemblies of organic molecules [18]. Based on the above aspects, an organic salt, 4-Dimethylaminopyridinium-3, 5-dicarboxybenzoate trihydrate (DMAPB) was synthesized and crystals were grown by slow solvent evaporation solution growth technique. In order to confirm the molecular structure and investigate the molecular packing in the crystal lattice, and hydrogen bonding interaction, the salt crystal was characterized through UV, FT-IR and NMR spectral studies, and Single Crystal XRD Analysis. Furthermore, the optical, luminescence, thermal, mechanical and SHG efficiency and laser damage threshold studies were investigated and reported.

2. Experimental details AR grade 4-dimethylaminopyridine and benzene 1,3,5tricarboxylic acid were purchased and used as such without further purification. Equimolar quantities of 4-dimethylaminopyridine and benzene 1,3,5-tricarboxylic acid were dissolved in Millipore water of resistivity 18.2 mU and pure methanol, respectively. When the two solutions were henceforth mixed together and stirred well for about 30 min on a temperature controlled magnetic stirrer, crystalline precipitate of the salt viz, 4-Dimethylaminopyridinium-3, 5dicarboxybenzoate trihydrate was precipitated. Hence, a saturated solution of the salt was prepared in methanol-acetone solvent mixture (1:1), stirred well to achieve homogeneous concentration over the entire volume of the solution and filtered through a quantitative 41 grade filter paper. The filtrate so obtained was collected in a 100 ml beaker and kept aside unperturbed in an atmosphere most suitable for the crystal growth. After a normal growth period of about 15 days, transparent good optical quality single crystals were harvested from the mother solution. The reaction scheme and the photograph as-grown title crystals are exhibited in Figs. 1 and 2, respectively. The chemical compounds purchased from Merck and Hi-Media were analar grade. Elemental analysis was performed on a Perkin Elmer 240C elemental analyzer at University of Hyderabad, Hyderabad, India. The UveVisible absorption spectrum was recorded in DMSO solvent employing a Systronics 2202 Double beam spectrophotometer (Resolution: 1 nm) in the wavelength range 200e600 nm. The UVeViseNIR transmittance spectrum of the title crystal was recorded employing a JASCO UVeViseNIR Spectrophotometer (Resolution: 1 nm) in the wavelength range 200e1500 nm. Fluorescence emission spectrum was recorded on a Horiba Jobin Yvon model FL3-22 Fluorolog spectrofluorimeter with an excitation wavelength of 280 nm. In order to confirm the presence of various functional groups, the title crystal was subjected to FTIR spectral analysis on a Perkin Elmer FT-IR 8000 spectrophotometer in the frequency range 4000e400 cm
1 using the KBr pellet method. 1H and 13C NMR spectra were recorded employing a Bruker AV III 500 MHz spectrometer using TMS as an internal

Fig. 2. As-grown single crystals of DMAPB crystal.

standard. The thermal stability of the title crystal was established by carrying out TG and DTA thermal analyses simultaneously on a NETZSCH STA 409 C/CD TG/DTA thermal analyzer (TG resolution: 0.1 mg, DTA resolution: 0.1 mV) in the temperature range between 0 and 800  C under nitrogen atmosphere at a heating rate of 10  C min
1. Vickers microhardness studies have been carried out on asgrown single crystals using HMV SHIMADZU tester (HMV SHIMADZU, make: HMV-2T). Dielectric studies for the grown crystals were carried out in the frequency range from 50 Hz to 5 MHz at different temperatures using Hioki LCR 3532-50 LCR meter. The prevalent SHG property was identified using Q-switched Nd: YAG laser emitting a fundamental wavelength of 1064 nm. The laser damage threshold value was measured using a Q-switched Nd:YAG laser with pulse width of 6 ns and repetition rate of 10 Hz. Single crystal X-ray diffraction data of DMAPB crystal was collected at 20  C on an Oxford Xcalibur Gemini EOS CCD diffractometer using Cu-Ka radiation equipped with a fine focused sealed tube. The unit cell parameters were determined and the data collections of DMAPB were performed using a graphite monochromated Cu-Ka radiation (l ¼ 1.54184 Å) by 4 and u scans. The structure of the crystal was solved by direct method [19] using SHELXS-97 and refined by full matrix least squares on F2 (SHELXL-97) [20]. All nonhydrogen atoms were refined anisotropically while the hydrogen atoms were placed in calculated positions and refined as riding atoms.

3. Results and discussion The purity and stoichiometric proportion of the elements (CHN)

Fig. 1. Reaction scheme of DMAPB crystal.

M. Rajkumar et al. / Optical Materials 72 (2017) 247e256

present in the synthesized compound were found by elemental analysis. The micro analysis results show that the compound contains C: 49.74% (49.78%), H: 5.74% (5.76%), N: 7.25% (7.29%). The analysis data indicate that the experimentally determined values are in very good agreement with theoretical values (given in brackets) within the limits of permissible error. The results further show that the crystal is free from impurities and contains three water molecules of crystallization. As has been observed in the Fig. 3, UVeVisible spectrum exhibits the characteristic absorption bands attributed to the usual p-p* and n-p* transitions taking place in the title compound. The p-p* transition appears as strong and intense band at 231 nm. The weak absorption band which appears as a hump at 284 nm is assigned to the n-p* transition of the C]O group present in the title compound. The recorded UVeVisible spectrum explicitly indicates the existence of the most probable p-p* and symmetry forbidden n-p* transitions of the salt crystal. As seen in the Fig. 4 (a), the attained percentage of transmission is 85 in the visible region and lower cut off wavelength is around 300 nm. Further, it is evident from the spectrum that there is no significant absorption noticed in the entire visible and NIR regions. The optical energy gap of the crystal is determined by converting UVeViseNIR transmission spectrum into Tauc's plot [21]. The optical absorption coefficient (a) was calculated using transmittance spectrum by the following relation

249

Fig. 4. (a)e(b). Optical Transmittance spectrum and Plot of (ahn)2 vs photon energy of DMAPB crystal.

where Eg is the optical band gap of the crystal and A is a constant. The intercept of linear fitting line of (ahy) 2 and hy gives the direct optical band gap (Fig. 4 (b)) and the value is found to be 3.97 eV. The high percentage transmittances coupled with wide transparency window and large band gap value enable the title crystal to be a potential candidate for optoelectronics and photonics applications [22]. Photoluminescence study is an important tool to identify the luminescence property, crystallinity and structural perfection of

the crystal [23]. While analyzing organic compounds, fluorescence materials find vast applications in biochemical, medical and chemical research fields. Molecules with aromatic ring or multiple conjugated double bonds with a high degree of resonance stability may be expected to be fluorescence materials [24]. Photoluminescence spectrum of DMAPB crystal was recorded between 300 and 685 nm and the spectrum shown in Fig. 5. From the emission spectrum, the broad emission peak observed at 491 nm corresponds to blue light emission and the sharp and intense peak at 575 confirms the green emission of the material. The strong and broad emissions are due to the existence of hydrogen bonding interaction and hence, the title crystal could be a useful material in optoelectronic and luminescence devices [25]. IR spectroscopy has been proven to recognize the proton transfer compounds [26]. The FT-IR spectrum is depicted in Fig. 6. The very strong and broad band appearing around 3228 cm
1 is due to the hydrogen bonded OeH stretching vibration. The bands which appear at 3123 and 3093 cm
1 correspond to the aromatic asymmetric and symmetric CeH stretching vibrations, respectively. The absorption bands at 2947 and 2926 cm
1 owe to the asymmetric and symmetric CeH stretching vibrations of the methyl groups, respectively. The NþeH stretching vibration expected to

Fig. 3. UVeVisible Spectrum of DMAPB crystal.

Fig. 5. Photoluminescence spectrum of DMAPB crystal.

a¼

2:3036 logð1=TÞ t

(1)

where T is the transmittance and t is the thickness of the crystal. As a direct band gap, for high photon energies (hy), the absorption coefficient (a) obeys the following relation




a¼

Aðhy
EgÞ1=2



hy

(2)

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M. Rajkumar et al. / Optical Materials 72 (2017) 247e256

Fig. 6. FT-IR spectrum of DMAPB crystal.

appear around 3000 cm
1 overlaps with the band due to aromatic CeH symmetric stretching vibration at 3093 cm
1. The huge band at 2400 cm
1 is noticed which may be a band derived from CO2 atmosphere. The strong band observed at 1707 cm
1 is attributed to C]O stretching vibration of carboxyl group. The aromatic C]C stretching vibration is exhibited at 1572 cm
1. The formation of the proton transfer compound is confirmed by appearance of strong asymmetric and symmetric stretching vibration bands of COOe group at 1563 and 1422 cm
1 respectively [27]. The asymmetric and symmetric in plane bending vibrations modes of the eCH3 group bring forth bands at 1439 and 1380 cm
1, respectively. The absorption band at 1215 cm
1 corresponds to the CeO stretching vibration. The absorption at 931 cm
1 is due to OeH out-of-plane bending vibration. The band at 893 cm
1 owes to the aromatic CeH out-of-plane bending mode. The vibrational bands observed below 500 cm
1 are due to the skeletal vibrations. The assignment of the well defined bands in the infrared spectrum is given in Table 1. NMR spectroscopic technique is the most powerful tool to elucidate and confirm molecular structure of the organic compounds. In 1H NMR spectrum, the carboxylic acid protons of 3, 5dicarboxybenzoate moiety appears in the downfield at d 11.2 ppm

Table 1 FT-IR spectral data of DMAPB crystal. Infrared frequencies (cm
1)

Assignments

3228 3123 3093 2947 2926 1707 1572 1563 1439 1422 1380 1215 931 893

OeH stretching frequency of carboxylic group Aromatic asymmetric CeH stretching vibration Aromatic symmetric CeH stretching vibration Aliphatic asymmetric CeH stretching vibration Aliphatic symmetric CeH stretching vibration C¼O stretching vibration of carbonyl group C¼C stretching vibration Asymmetric stretching vibration of COO
group Asymmetric bending vibration of CH3 group Symmetric stretching vibration of COO
group Symmetric bending vibration of CH3 group CeO stretching vibration OeH out-of-plane bending vibration CeH out-of-plane bending vibration

as a singlet. Another singlet signal appearing at d 8.6 ppm is attributed to the C2, C4 and C6 aromatic protons of the same kind in 3, 5-dicarboxybenzoate moiety in the salt crystal. The C2 and C6 aromatic protons of the same kind in 4-dimethylaminopyridinium moiety appear as a doublet centered at d 8.2 ppm. Another doublet centered at d 6.9 ppm is due to C3 and C5 aromatic protons in the same moiety. The singlet signal at d 2.1 ppm owes to methyl protons in the 4-dimethylaminopyridinium moiety in the salt crystal. In 13C NMR spectrum, the appearance of six distinct carbon signals in the spectrum explicitly confirms the established molecular structure of DMAPB salt crystal. In the downfield, carbon signal at d 166.80 ppm owes to the highly deshielded carboxyl carbon of the 3,5-dicarboxybenzoate moiety. The signal at d 142.50 ppm is assigned to the C4 carbon of the 4-dimethylaminopyridinium moiety. The signal at d 133.78 ppm is due to the C1 and C5 carbons of same kind in 4-dimethylaminopyridinium moiety. The signal at d 133.06 ppm is attributed to the C2, C4 and C6 carbons of the same kind in 3,5-dicarboxybenzoate moiety. The signal at d 107.32 ppm is attributed to the C3 and C5 carbons of same kind in 4-dimethylaminopyridinium moiety. The signal at d 31.16 ppm is due to methyl carbon atoms of 4-dimethylaminopyridinium moiety. The carbon signal for C1, C3 and C5 carbons of the same kind in 3, 5dicarboxybenzoate moiety is getting sub-merged under the signal due to C2 and C6 carbon atoms of 4-dimethylaminopyridinium moiety. The 13C NMR and 1H NMR spectra of DMAPB crystal are depicted in Figs. 7 and 8, respectively and the corresponding spectral data of the title molecule are summarized in Table 2. The single crystal XRD analysis was carried out on the well grown single crystal to establish its molecular structure and identify the direction of specific OeH/O, NeH/O and CeH/O hydrogen bonds between the constituent species. The crystallographic data indicate that the crystal belongs to orthorhombic crystal system with non-centrosymmetric space group, Pna21. Lattice parameters are a ¼ 7.51903 (19), b ¼ 15.3216 (4) c ¼ 15.8284 (4) Å, a ¼ b ¼ c ¼ 90 and the volume of the unit cell is found to be 1823.49 (8) Å3. The crystallographic data and structure refinements of DMAPB crystal are given in Table 3. Fig. 9 shows the ORTEP view of the molecule drawn at 50% probability thermal displacement ellipsoids with the atom numbering scheme. The packing arrangement of the molecule

M. Rajkumar et al. / Optical Materials 72 (2017) 247e256

251

Fig. 7. 1H NMR spectrum of DMAPB crystal.

Fig. 8.

13

C NMR spectrum of DMAPB crystal.

viewed down ‘a’, ‘b’ and ‘c’-axes is shown in Fig. 10. The selected bond lengths and bond angles are given in Table 4. The carboxyl proton at C14 of the benzene 1,3,5-tricarboxylic acid was transferred to ring nitrogen atom of the 4-dimethylaminopyridine which is confirmed by the presence of almost equal CeO bond lengths (1.252 (2) Å, C (14)eO (1), and 1.254 (2) Å, C (14)eO (2)) due to the

existence of resonance in carboxylate ion [27, 28]. The asymmetric unit contains one 4-dimethylaminopyridinium ion, one 3, 5dicarboxybenzoate ion and three water molecules. Further, the molecular salt forms NeH/O hydrogen bond between NeH of 4dimethylaminopyridinium and the O
of 3, 5-dicarboxybenzoate moieties with NeO distance of 2.714 (2) Å. Moreover, crystal

252

M. Rajkumar et al. / Optical Materials 72 (2017) 247e256 Table 2 1 H and 13C NMR chemical shift values of DMAPB crystal. Chemical shift values (ppm)

Assignments

1

H NMR spectral data 11.2(s) 8.6(s) 8.2(s) 6.9(s) 2.1(s) 13 C NMR spectral data 166.80 142.50 133.78 133.06 107.32 31.16

Carboxylic proton of 3, 5-dicarboxybenzoate moiety C2, C4 and C6 aromatic protons of the same kind in 3, 5-dicarboxybenzoate moiety C2 and C6 aromatic protons of the same kind in 4-dimethylaminopyridinium moiety C3 and C5 aromatic protons of the same kind in 4-dimethylaminopyridinium moiety Methyl protons of 4-dimethylaminopyridinium moiety Carboxyl carbon of the 3, 5-dicarboxybenzoate moiety C4 carbon of the 4-dimethylaminopyridinium moiety C2 and C6 carbons of same kind in 4-dimethylaminopyridinium moiety C2, C4 and C6 carbons of the same kind in 3, 5-dicarboxybenzoate moiety C3 and C5 carbons of same kind in 4-dimethylaminopyridinium moiety. Methyl carbon atoms of 4-dimethylaminopyridinium moiety

Table 3 Crystal data and structure refinement for DMAPB crystal. Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions

Volume Z Density (calculated) Absorption coefficient F (000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta ¼ 71.80 Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2sigma(I)] R indices (all data) Largest diff. peak and hole

C16 H22 N2 O9 386.36 293 (2) K 1.54184 Å Orthorhombic P na21 a ¼ 7.51903 (19) Å a ¼ 90 b ¼ 15.3216 (4) Å b ¼ 90 c ¼ 15.8284 (4) Å g ¼ 90 1823.48 (8) Å3 4 1.407 Mg/m3 0.995 mm
1 816 0.42  0.30  0.18 mm3 4.02e71.80 .
5  h  9,
18  k  13,
16  l  19 4161 2509 [R (int) ¼ 0.0130] 97.9% Full-matrix least-squares on F2 2509/1/273 0.925 R1 ¼ 0.0325, wR2 ¼ 0.0951 R1 ¼ 0.0334, wR2 ¼ 0.0965 0.207 and
0.178 e.Å
3

structure composed of anion, cation and three water molecules introduces additional hydrogen bond acceptor sites (three carboxyl groups) to form OeH/O and CeH/O hydrogen bonds between neighbouring moieties. The lattice water molecule acts as bis(monodentate) donor to form two OeH/O hydrogen bonds with O atom of the carboxylate group and water molecule in bifurcate mode. This water molecule also functions as an acceptor to make a CeH/O (C (1)eH (2) … O (7)) interaction with the cation in which the CeO distance is 3.318 (3) Å. Although the salt forms the acid to amide interaction to bind the two components together, water molecules are involved in a variety of OeH/O hydrogen bonds to construct the supramolecular assembly. The hydrogen bond interactions involved in the DMAPB is shown in Table 5. To establish the thermal stability of DMAPB crystal, the TG/DTA thermal analyses were carried out simultaneously and the thermogram depicted in Fig. 11 From the TG curve, it is obvious that the material is stable up to 300  C and decomposes immediately after melting. The decomposition takes place in a single step commencing at about 300  C and ending at 345  C, with the loss of about 92% of the sample as carbon monoxide, Carbon dioxide, Nitrogen dioxide and a mixture of hydrocarbon gases. It is observed that the melting point of the material takes place in the vicinity of

300  C. Before melting, the weight loss takes place gradually which is due to the removal of physically adsorbed water molecules on the lattice. Further, it indicates no phase transition before melting. The DTA curve indicates the same changes shown by TG curve. The sharpness of the endothermic peak observed at 300  C indicates the good degree of crystallinity and purity of the DMAPB crystal. The second endothermic peak observed at 350  C is attributed to the major decomposition temperature of the substance. As the hardness of the crystal is one of the important parameters in determining the applicability of the specific device to its performance, it is vital to carry out hardness studies for the grown crystal. Micro hardness studies have been carried out on as-grown single crystals using HMV SHIMADZU tester, fitted with diamond Vickers pyramidal indenter. Hardness of the crystals was calculated using the relation

  . P Hv ¼ 1:8544 2 Kg mm2 d

(3)

where Hv is Vickers micro hardness number, P is the indenter load and d is the diagonal length of the impression. The applied load was varied from 25 to 100 g. When the load was increased to 100 g, cracks were developed on the smooth surface of the crystal. The plot of variation of Vickers hardness with applied load is shown in Fig. 12 (a). From the plot, it is understood that the grown crystal obeys reverse indentation size effect which means hardness increases with increasing the applied load [29]. By plotting log p verses log d (Fig. 12(b)), work hardening coefficient value (n) was found to be 3.05. It is noted that the work hardening coefficient lies between 1 and 1.6 for hard materials and above 1.6 soft materials [30]. Hence, it is concluded that the title crystal belongs to the soft material category. Dielectric measurement paves the way to characterize the electrical response of the solids and can be correlated with electro-optic property of the crystal [31]. The dielectric study of the grown crystal was carried out from the frequency range of 50 Hz - 5 MHz at different temperatures (303 K, 313 K, 333 K, 353 K, and 373 K). The dielectric constant was calculated using the given formula

εr ¼

Cp d εo A

(4)

where, Cp is the measured parallel capacitance, d is the thickness of the crystal, A is the electrode area, εr dielectric constant and εo is the vacuum permittivity (8.85  10
12 F/m). The variations of dielectric constant and loss verses frequency at different temperatures are depicted in Fig. 13(a). From the results, it is clear that dielectric constant and loss decrease with increase in frequency and temperature. The dielectric constant values are high at low frequencies

M. Rajkumar et al. / Optical Materials 72 (2017) 247e256

Fig. 9. ORTEP diagram of DMAPB crystal.

Fig. 10. Packing arrangement of molecule viewed down the ‘a’, ‘b’ and ‘c’-axes showing the hydrogen bond interactions.

253

254

M. Rajkumar et al. / Optical Materials 72 (2017) 247e256

Table 4 Bond lengths [Å] and Bond angles [ ] for DMAPB crystal. O (1)eC (14) O (5)eC (16) O (6)eC (16) O (2)eC (14) C (16)eC (12) O (4)eC (15) C (10)eC (11) C (10)eC (9) C (10)eC (15) C (14)eC (8) C (11)eC (12) C (12)eC (13) C (13)eC (8) C (9)eC (8) C (15)eO (3) C (4)eC (5) C (4)eC (3) N (1)eC (1) N (1)eC (5) C (3)eN (2) C (3)eC (2) C (2)eC (1) N (2)eC (6) N (2)eC (7) O (6)-C (16)-O (5) O (6)-C (16)-C (12) O (5)-C (16)-C (12) C (11)-C (10)-C (9)

1.252 (2) 1.312 (3) 1.203 (2) 1.254 (2) 1.497 (2) 1.316 (3) 1.387 (3) 1.391 (3) 1.497 (3) 1.509 (3) 1.390 (2) 1.393 (3) 1.391 (2) 1.391 (2) 1.194 (3) 1.362 (3) 1.419 (3) 1.337 (3) 1.337 (3) 1.332 (3) 1.414 (3) 1.350 (3) 1.456 (3) 1.455 (3) 123.60 (18) 122.91 (18) 113.47 (16) 120.15 (17)

C (11)-C (10)-C (15) C (9)-C (10)-C (15) O (1)-C (14)-O (2) O (1)-C (14)-C (8) O (2)-C (14)-C (8) C (10)-C (11)-C (12) C (11)-C (12)-C (13) C (11)-C (12)-C (16) C (13)-C (12)-C (16) C (8)-C (13)-C (12) C (8)-C (9)-C (10) C (9)-C (8)-C (13) C (9)-C (8)-C (14) C (13)-C (8)-C (14) O (3)-C (15)-O (4) O (3)-C (15)-C (10) O (4)-C (15)-C (10) C (5)-C (4)-C (3) C (1)-N (1)-C (5) N (2)-C (3)-C (2) N (2)-C (3)-C (4) C (2)-C (3)-C (4) N (1)-C (5)-C (4) C (1)-C (2)-C (3) C (3)-N (2)-C (6) C (3)-N (2)-C (7) C (6)-N (2)-C (7) N (1)-C (1)-C (2)

121.87 (18) 117.97 (17) 123.84 (19) 117.98 (16) 118.16 (16) 119.68 (18) 120.06 (17) 121.73 (17) 118.18 (16) 120.48 (16) 120.56 (17) 119.06 (17) 120.79 (16) 120.14 (15) 123.6 (2) 123.2 (2) 113.20 (17) 119.94 (18) 120.15 (19) 121.74 (18) 122.30 (18) 115.96 (19) 121.64 (19) 120.53 (19) 121.2 (2) 122.0 (2) 116.8 (2) 121.75 (19)

Fig. 11. TG/DTA thermogram of DMAPB crystal.

NLO devices, electro-optic and photonic applications [33]. The modified Kurtz-Perry powder technique initially screens the materials for second harmonic generation [34]. A Q-switched Nd:YAG laser with fundamental laser beam of 1064 nm wave-

Table 5 Hydrogen bonding geometry of DMAPB crystal. …

Acceptor

D _H

N (1)eH (1) … O (1) O (4)-H (4A) … O (9) O (5)-H (5A) … O (7) O (7)eH (71) … O (8) O (7)eH (72) … O (2) O (8)eH (81) … O (6) O (8)eH (81) … O (3) O (8)eH (82) … O (9) O (9)eH (91) … O (1) O (9)eH (92) … O (2) C (1)eH (2) … O (7) C (2)eH (3) … O (6) C (5)eH (5) … O (3)

0.90 0.82 0.82 0.93 0.79 0.89 0.89 0.93 0.94 0.82 0.93 0.93 0.93

Donor- H

H (3)

(3) (3) (4) (4) (4) (5) (3)

…

1.86 1.88 1.8 1.85 1.96 2.57 2.31 1.98 1.91 1.92 2.5 2.59 2.41

…

A

D

A

D_ H

(3)

2.714 (2) 2.6753 (19) 2.605 (2) 2.759 (3) 2.7441 (19) 3.024 (3) 3.132 (3) 2.882 (3) 2.7940 (18) 2.708 (2) 3.318 (3) 3.251 (3) 3.149 (3)

157 164 167 169 172 112 154 164 154 161 147 129 136

(3) (3) (4) (4) (4) (5) (3)

…

A

Symmetry code

(3)

3/2-x,1/2 þ y,-1/2 þ z x,y,1 þ z

(3) (4) (3) (3) (4) (4) (3)

1-x,1/2 þ y,1-z 3/2-x,1/2 þ y,-1/2 þ z
1þx,y,z
1/2 þ x,y,3/2-z 1/2-x,-1/2 þ y,1/2 þ z 3/2-x,1/2 þ y,-1/2 þ z 2-x,1/2 þ y,1-z
1/2 þ x,y,1/2-z
1/2 þ x,y,1/2-z
1/2 þ x,y,3/2-z

Table 6 Comparisons of laser damage value of DMAPB crystal with NLO crystals. Crystal

Laser damage Threshold Value (GW/cm2)

Reference

KDP Urea Dimethyl amino pyridinium 4-nitrophenolate 4-nitrophenol L-Prolinium tartrate Diethylammonium p-hydroxybenzoate 4-Dimethylaminopyridinium-3, 5-dicarboxybenzoate trihydrate

0.2 1.5 2.24 5.9 6.9 1.06

[37] [36] [38] [36] [36] Present work

due to the contribution of ionic, electronic, orientational and space charge polarization and low at high frequency owing to the loss of magnitude of these polarizations gradually [32]. The reason for the variation of dielectric constant and loss with respect to the temperature is attributed to the thermally generated charge carriers and impurity dipoles. The variations of loss verses frequency at different temperatures are presented in Fig. 13(b). The low dielectric loss at higher frequencies clearly reveals that the title crystal possesses high optical quality and has lesser defects which are most important and desirable property of the crystalline materials for

length, 6 ns pulse width with 10 Hz pulse rate and 0.5 mW energy per pulse was made to fall normally on the cell containing powdered crystalline material. A laser beam of 1064 nm wavelength is passed through iris diaphragm to remove flash lamp component around laser beam then passed through 1064 nm interference filter to remove other components present in the laser beam. The laser beam was allowed to incident on the surface of the powdered compound at an angle of 45 , packed in sample holder with front of 1 mm thick quartz plate. The output light was collected at an angle 90 (with direction of incidence) that was

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255

Fig. 12. (a)e(b). Vickers hardness vs load P and log d vs log p of PCHBS Crystal. Fig. 14. SHG conversion efficiency of the grown crystal compared with KDP material.

surface damage threshold of the crystal was calculated using the expression

Pd ¼

E

tpr2

(5)

where E is the input energy (mJ), t is the pulse width (ns) and r is the radius of the spot (mm). When laser beam with different energies (1.5 mJe3 J) was shot on the crystal surface, the damage was observed on the crystal at the energy of 306 mJ. The laser damage threshold value was 1.06 GW/cm2 for Nd:YAG laser radiation and hence the title crystal is suitable for NLO device applications. The laser damage threshold value of DMAPB crystal was compared with some inorganic and organic NLO material and is given in Table 6. 4. Conclusion Fig. 13. (a)e(b). Plot of dielectric constant and dielectric loss versus Log f at different temperatures for DMAPB crystal.

passed through 532 nm interference filter to remove IR components and fed to optical fiber based UVevis spectrophotometer to measure intensity. The emission of green light confirms the Second Harmonic Generation behaviour of the title crystal. The intensity was measured and compared with intensity of 532 nm light by KDP polycrystalline material. From the Fig. 14, it is observed that the relative SHG efficiency of DMAPB was found to be 0.89 times that of KDP material. The operation of NLO devices such as second harmonic generation, THz wave generation and electro-optic modulation using single crystals involves the exposure of these materials to high power laser light [35]. The laser damage threshold density of crystal determines its utility for nonlinear optical applications. The laser damage threshold depends upon the various laser parameters such as wavelength, energy, pulse duration, longitudinal and transverse mode structures, beam size, location of beam, etc [36]. A fundamental wavelength, 1064 nm, with a pulse width of 6 ns and a repetition rate of 10 Hz was used to measure the laser damage threshold of DMABS crystal. The laser beam of diameter 1 mm was focused on the crystal. The sample was placed at the focus of a plano-convex lens of focal length 15 cm. An attenuator was used to vary the energy of the laser pulses with a polarizer and a half-wave plate. The pulse energy of each shot was measured using the combination of a phototube and an oscilloscope. The

A hydrogen bonded SHG active organic salt, 4Dimethylaminopyridinium-3, 5-dicarboxybenzoate trihydrate was synthesized and grown as single crystals by slow solvent evaporation solution growth technique. The molecular structure was established by single crystal XRD analysis. The single crystal data indicates that the grown crystal belongs to orthorhombic crystal system with non-centrosymmetric space group, Pna21 and confirms the existence of extensive NeH/O, OeH/O and CeH/O hydrogen bonding interactions. The UVeVisible spectrum exhibits absorption bands attributed to p-p* and n-p* transitions of the constituent moieties. The UVeViseNIR transmission spectrum attests the suitability of the title crystal for various optical applications. Photoluminescence spectrum shows that the title crystal has blue and green fluorescence emissions at 491 and 575 nm, respectively. The formation of the proton transfer compound was confirmed by the appearance of two characteristic bands for carboxylate group using FT-IR spectral studies. The established molecular structure was further confirmed by 1H and 13C NMR spectroscopic technique. The TG/DTA analysis reveals that the crystal is thermally stable up to 300  C. The Vickers microhardness study confirms that the grown crystal exhibits Reverse Indentation Size Effect (RISE) and also falls under the soft material category. The low value of dielectric constant and loss indicate that the title crystal is suitable for electro-optic applications. The relative SHG efficiency of DMAPB crystal was found to be 0.89 times that of standard KDP crystal. The laser damage threshold value is found to be 1.06 GW/cm2 at a 1064 nm wavelength of Nd:YAG laser. The

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good transparency with wide band gap, luminescence property, good thermal stability, low dielectric constant and loss and high laser damage threshold prove the utility of the crystal for NLO device fabrications and electro-optic applications. Hence, DMAPB crystal is a promising optical material with adequate LDT which can be used for laser assisted NLO applications such as photonics, optical limiting, SHG, data processing and data storage devices. Acknowledgements The authors acknowledge the School of Chemistry, University of Hyderabad, Hyderabad for providing instrumental facilities and also thank Dr. Gajanan G. Muley, Sant Gadge Baba Amravati University, Amravati, India to carry out the SHG measurement. One of the authors M. Rajkumar thanks the UGC Networking Centre, School of Chemistry, University of Hyderabad for the award of visiting research fellowship to use the facilities at school of chemistry, University of Hyderabad, Hyderabad and grateful to Prof. S. K. Das, University of Hyderabad, Hyderabad for his support and help. References [1] Manoj K. Gupta, Nidhi Sinha, Binay Kumar, Growth and characterization of new semi-organic l-proline strontium chloride monohydrate single crystals, Phys. B Condens. Matter 406 (1) (2011) 63e67. [2] P. Nagapandiselvi, C. Baby, R. Gopalakrishnan, Synthesis, growth, structure and nonlinear optical properties of a semiorganic 2-carboxy pyridinium dihydrogen phosphate single crystal, Opt. Mater. 47 (2015) 398e405. [3] R. Nagalakshmi, V. Krishnakumar, N. Sudharsana, A. Wojciechowski, M. Piasecki, I.V. Kityk, Michael Belsley, Dmitry Isakov, Studies on physicochemical properties of hydroxyethylammonium (l) tartrate monohydrate single crystals, Phys. B Condens. Matter 406 (21) (2011) 4019e4026. [4] E. Selvakumar, A. Chandramohan, G. Anandha Babu, P. Ramasamy, Synthesis, growth, structural, optical and thermal properties of a new organic salt crystal: 3-nitroanilinium trichloroacetate, J. Cryst. Growth 401 (2014) 323e326. [5] T. Baraniraj, P. Philominathan, Growth and characterization of organic nonlinear optical material: benzilic acid, J. Cryst. Growth 311 (15) (2009) 3849e3854. [6] C. Ji, T. Chen, Z. Sun, Y. Ge, W. Lin, J. Luo, Q. Shi, M. Hong, Bulk crystal growth and characterization of imidazolium l-tartrate (IMLT): a novel organic nonlinear optical material with a high laser-induced damage threshold, CrystEngComm 15 (2013) 2157e2162. [7] L.R. MacGillivray, G.S. Papaefstathiou, T. Fri
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