Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 929–937
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal S. Sudhahar, M. Krishna Kumar, B.M. Sornamurthy, R. Mohan Kumar ⇑ Department of Physics, Presidency College, Chennai 600 005, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Organic 4MPHB crystal was grown by
slow evaporation method. 4MPHB belongs to monoclinic crystal
system with space group P21/c. Refractive index of 4MPHB crystal is
found to be 1.44. Crystal possesses high LDT value of
5.14 GW/cm2. SHG efficiency of 4MPHB is 2.79
times that of KDP crystal.
a r t i c l e
i n f o
Article history: Received 27 July 2013 Received in revised form 16 September 2013 Accepted 26 September 2013 Available online 7 October 2013 Keywords: Crystal structure Spectral analysis Thermal analysis Birefringence NLO material
a b s t r a c t Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV–visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications. Ó 2013 Elsevier B.V. All rights reserved.
Introduction During the past two decades, there has been an intensive research effort on exploring and developing new materials for variety of nonlinear optical (NLO) applications. Nonlinear optical materials play a vital role in the photonics technology including optical information processing, telecommunications, optical storage and ⇑ Corresponding author. Tel.: +91 9444600670; fax: +91 44 28510732. E-mail address: [email protected] (R. Mohan Kumar). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.09.072
more recently THz generation and detection [1,2]. Considerable research efforts have already been made in exploring novel organic materials for their potential use in variety of applications. The materials, which could produce green/blue laser light and could withstand at high-energy light radiation, are of great importance for future technology. High nonlinearities and the almost purely electronic origin of the nonlinear effects in organics with short response times make them highly superior to their inorganic counterparts [3]. Organic compounds containing push–pull conjugation can present large optical second-order molecular polarizabilities
930
S. Sudhahar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 929–937
and possess application in second-order nonlinear optical devices. Depolarization and intermolecular charge transfer effect of p-electrons in the molecules can cause large and fast nonlinear responses. The second harmonic generation properties of the materials require non-centrosymmetric crystal structure. It possesses parallel alignment of molecules, which results in high hyperpolarazibility and large second-order nonlinear susceptibilities for the crystals. In the case of centrosymmetric crystals, the even order nonlinear optical susceptibilities are zero in the electric dipole approximation [4]. Only a few reports are available about the centrosymmetric media [5–8] and film [9], which also exhibit second harmonic generation (SHG) property. In this present study, we report the synthesis and growth of 4-methylpyridinium 4hydroxybenzoate (4MPHB) compound and the grown crystal were studied by different characterization techniques. Experimental Fig. 2. Photograph of as-grown 4MPHB single crystal.
Synthesis and crystal growth Analytical grade 4-picoline (C6H7N) and p-hydroxybenzoic acid (C7H6O3) reagents were used for the synthesis of 4-methylpyridinium 4-hydroxybenzoate (4MPHB) compound. The stoichiometric equimolar amounts of precursors were used for the synthesis of title compound. p-Hydroxybenzoic acid was first dissolved in methanol thoroughly by continuous stirring and then the measured amount of 4-picoline was added dropwise into the solution. The solution was stirred for about 12 h to complete the reaction process (Fig. 1). The experiment was carried out at room temperature. The homogeneous solution was filtered using high quality Whatman filter paper to remove impurities from the solution and then it was allowed for slow evaporation. Good quality 4MPHB seed crystals were harvested. The synthesized compound was recrystallized at least three times in methanol to improve the purity of the compound. The solubility of the 4MPHB compound was estimated to be 17.2 g in 100 ml of methanol at 35 °C. The saturated growth solution was prepared, filtered and allowed for slow evaporation at a constant temperature of 35 °C using constant temperature bath with an accuracy of ±0.01 °C. After a period of 3–4 weeks, optical quality crystal of size 18 13 3 mm3 was harvested as shown in Fig. 2.
and Bruker AVANCE III 500 MHz spectrometers respectively. Thermal studies for the crystal sample were carried out in nitrogen atmosphere using SII TG/DTA 6300 EXSTAR instrument. Perkin–Elmer Lambda35 spectrometer was used to record UV–visible spectrum for the grown crystal. Photoluminescence excitation spectrum was recorded for the compound using RF-5301 spectrometer. Refractive index of 4MPHB crystal was measured using Metricon prism coupler Model 2010/M in TE mode. Birefringence of 4MPHB crystal was studied using modified channel spectrum measurement. Kurtz–Perry powder technique was employed to ensure the SHG efficiency of the 4MPHB crystal using 1064 nm as a fundamental wavelength. Laser damage threshold study was done on the 4MPHB crystal using 1064 nm Nd:YAG laser radiation. Microhardness measurement was carried out on the grown crystal using Leitz–Weitzler hardness tester fitted with a diamond indenter.
Results and discussion Crystal structure refinement studies
Bruker Kappa APEXII CCD single crystal X-ray diffractometer was used for the crystal structure data collection at 293 K and the crystal structure was solved using SHELXL-97 refinement program. Powder X-ray diffraction analysis was performed to confirm the grown crystal using Bruker AXSCAD4 diffractometer. Infrared, Raman and nuclear magnetic resonance spectroscopic methods were employed to elucidate the molecular structure of the compound using JASCO FTIR 410, Bruker RFS 27 (100 mW laser source)
X-ray diffraction study was carried out for crystal structure determination for the 4-methylpyridinium 4-hydroxybenzoate (4MPHB) single crystal at 293 K. Crystal structure was solved by direct method of SHELXS-97 program and refinement was made by full-matrix least-squares method. The 4MPHB crystal belongs to monoclinic crystal system with centrosymmetric, P21/c space group. The estimated lattice parameters are a = 7.479 Å, b = 11.671 Å, c = 13.52 Å, b = 100.217° and V = 1161.4 Å3 with Z = 4 [10]. Thermal ellipsoid plot for the molecular structure in the asymmetric unit cell is shown in Fig. 3. The crystal structure refinement parameters for 4MPHB are listed in Table 1 and the
Fig. 1. Synthesis scheme for 4MPHB compound.
Fig. 3. Thermal ellipsoid plot for 4MPHB crystal structure.
Characterization
S. Sudhahar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 929–937
931
Table 1 Crystal data and structure refinement for 4MPHB. Identification code Empirical formula Formula weight Crystal system Space group Unit cell dimensions
SHELXL C6H8N+C7H5O3 231.24 Monoclinic P21/c a = 7.479 (5) Å b = 11.671 (4) Å c = 13.520 (5) Å a = c = 90°, b = 100.217 (5)° 1161.4 (10) Å3 4, 1.322 488 0.24 0.20 0.18 295 Mo Ka (0.71073) 2.3–27.1° 1939 0.043, 0.128, 1.06
Volume (V) Z, D (calc) (g/cm3) F (0 0 0) Crystal size (mm) Temperature (K) Radiation (Å) Theta Min–Max (Deg) Observed data [I > 2.0 sigma (I)] R, wR2, S
hydrogen bond geometry is shown in Table 2. In the 4MPHB molecular structure (Fig. 3), the H atom between O1 and N1 is disordered over two sites with associated site occupancy of 0.73 (4) and 0.27 (4) respectively. The appearance of H atom near O1 and N1 is clearly identified and fixed subsequently from the different element density map. The same type of positional disorder was already observed in 4,40 -bipyridyl-tartaric acid structure [11]. In the supramolecular arrangement of molecules in 4MPHB crystal, the 4-hydroxy benzoate molecules are linked through O3AH3A O2 hydrogen bonds to form a molecular chain. Due to the presence of disordered hydrogen atom between the O1 and N1 atoms, 73% of 4-methylpyridine molecules are linked through O1AH1A N1 hydrogen bond (Fig. 4a), whereas 27% of the 4methylpyridinium ion are linked through N1AH1A O1 hydrogen bonds (Fig. 4b) in the supramolecular arrangement. The adjacent molecular chains are linked through strong CAH O hydrogen bonds. A R22(8) ring formed by C6AH6. . .O3 connects the adjacent molecular chains, which along with other CAH O hydrogen bonds generates a three dimensional molecular network in the crystalline solid. Even though the compound crystallizes in centrosymmetric space group P21/c, the partial (unequal) transfer of H from O1 to N1 causes a partial difference in the supramolecular arrangement of the crystalline solid. This partial protonation leads charge distortion and it is responsible for the presence of SHG activity in the present system. It concludes that the SHG generation of the crystal is due to charge distribution at the molecular level of supramolecular structures. The experimental details of the SHG in the crystalline solid are discussed in the Section 3.8. Powder X-ray diffraction analysis was performed to confirm the crystallinity and also to estimate the lattice parameters. The sample was scanned over the range of 10–70° at a scan rate of 1 °/min. The powder Xray diffraction pattern of 4-methylpyridinium 4-hydroxybenzoate crystal is shown in Fig. 5.
Table 2 Hydrogen-bond geometry (Å, °). D—H A
d (D—H)
d (HA)
d (DA)
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal S. Sudhahar, M. Krishna Kumar, B.M. Sornamurthy, R. Mohan Kumar ⇑ Department of Physics, Presidency College, Chennai 600 005, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Organic 4MPHB crystal was grown by
slow evaporation method. 4MPHB belongs to monoclinic crystal
system with space group P21/c. Refractive index of 4MPHB crystal is
found to be 1.44. Crystal possesses high LDT value of
5.14 GW/cm2. SHG efficiency of 4MPHB is 2.79
times that of KDP crystal.
a r t i c l e
i n f o
Article history: Received 27 July 2013 Received in revised form 16 September 2013 Accepted 26 September 2013 Available online 7 October 2013 Keywords: Crystal structure Spectral analysis Thermal analysis Birefringence NLO material
a b s t r a c t Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV–visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications. Ó 2013 Elsevier B.V. All rights reserved.
Introduction During the past two decades, there has been an intensive research effort on exploring and developing new materials for variety of nonlinear optical (NLO) applications. Nonlinear optical materials play a vital role in the photonics technology including optical information processing, telecommunications, optical storage and ⇑ Corresponding author. Tel.: +91 9444600670; fax: +91 44 28510732. E-mail address: [email protected] (R. Mohan Kumar). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.09.072
more recently THz generation and detection [1,2]. Considerable research efforts have already been made in exploring novel organic materials for their potential use in variety of applications. The materials, which could produce green/blue laser light and could withstand at high-energy light radiation, are of great importance for future technology. High nonlinearities and the almost purely electronic origin of the nonlinear effects in organics with short response times make them highly superior to their inorganic counterparts [3]. Organic compounds containing push–pull conjugation can present large optical second-order molecular polarizabilities
930
S. Sudhahar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 929–937
and possess application in second-order nonlinear optical devices. Depolarization and intermolecular charge transfer effect of p-electrons in the molecules can cause large and fast nonlinear responses. The second harmonic generation properties of the materials require non-centrosymmetric crystal structure. It possesses parallel alignment of molecules, which results in high hyperpolarazibility and large second-order nonlinear susceptibilities for the crystals. In the case of centrosymmetric crystals, the even order nonlinear optical susceptibilities are zero in the electric dipole approximation [4]. Only a few reports are available about the centrosymmetric media [5–8] and film [9], which also exhibit second harmonic generation (SHG) property. In this present study, we report the synthesis and growth of 4-methylpyridinium 4hydroxybenzoate (4MPHB) compound and the grown crystal were studied by different characterization techniques. Experimental Fig. 2. Photograph of as-grown 4MPHB single crystal.
Synthesis and crystal growth Analytical grade 4-picoline (C6H7N) and p-hydroxybenzoic acid (C7H6O3) reagents were used for the synthesis of 4-methylpyridinium 4-hydroxybenzoate (4MPHB) compound. The stoichiometric equimolar amounts of precursors were used for the synthesis of title compound. p-Hydroxybenzoic acid was first dissolved in methanol thoroughly by continuous stirring and then the measured amount of 4-picoline was added dropwise into the solution. The solution was stirred for about 12 h to complete the reaction process (Fig. 1). The experiment was carried out at room temperature. The homogeneous solution was filtered using high quality Whatman filter paper to remove impurities from the solution and then it was allowed for slow evaporation. Good quality 4MPHB seed crystals were harvested. The synthesized compound was recrystallized at least three times in methanol to improve the purity of the compound. The solubility of the 4MPHB compound was estimated to be 17.2 g in 100 ml of methanol at 35 °C. The saturated growth solution was prepared, filtered and allowed for slow evaporation at a constant temperature of 35 °C using constant temperature bath with an accuracy of ±0.01 °C. After a period of 3–4 weeks, optical quality crystal of size 18 13 3 mm3 was harvested as shown in Fig. 2.
and Bruker AVANCE III 500 MHz spectrometers respectively. Thermal studies for the crystal sample were carried out in nitrogen atmosphere using SII TG/DTA 6300 EXSTAR instrument. Perkin–Elmer Lambda35 spectrometer was used to record UV–visible spectrum for the grown crystal. Photoluminescence excitation spectrum was recorded for the compound using RF-5301 spectrometer. Refractive index of 4MPHB crystal was measured using Metricon prism coupler Model 2010/M in TE mode. Birefringence of 4MPHB crystal was studied using modified channel spectrum measurement. Kurtz–Perry powder technique was employed to ensure the SHG efficiency of the 4MPHB crystal using 1064 nm as a fundamental wavelength. Laser damage threshold study was done on the 4MPHB crystal using 1064 nm Nd:YAG laser radiation. Microhardness measurement was carried out on the grown crystal using Leitz–Weitzler hardness tester fitted with a diamond indenter.
Results and discussion Crystal structure refinement studies
Bruker Kappa APEXII CCD single crystal X-ray diffractometer was used for the crystal structure data collection at 293 K and the crystal structure was solved using SHELXL-97 refinement program. Powder X-ray diffraction analysis was performed to confirm the grown crystal using Bruker AXSCAD4 diffractometer. Infrared, Raman and nuclear magnetic resonance spectroscopic methods were employed to elucidate the molecular structure of the compound using JASCO FTIR 410, Bruker RFS 27 (100 mW laser source)
X-ray diffraction study was carried out for crystal structure determination for the 4-methylpyridinium 4-hydroxybenzoate (4MPHB) single crystal at 293 K. Crystal structure was solved by direct method of SHELXS-97 program and refinement was made by full-matrix least-squares method. The 4MPHB crystal belongs to monoclinic crystal system with centrosymmetric, P21/c space group. The estimated lattice parameters are a = 7.479 Å, b = 11.671 Å, c = 13.52 Å, b = 100.217° and V = 1161.4 Å3 with Z = 4 [10]. Thermal ellipsoid plot for the molecular structure in the asymmetric unit cell is shown in Fig. 3. The crystal structure refinement parameters for 4MPHB are listed in Table 1 and the
Fig. 1. Synthesis scheme for 4MPHB compound.
Fig. 3. Thermal ellipsoid plot for 4MPHB crystal structure.
Characterization
S. Sudhahar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 929–937
931
Table 1 Crystal data and structure refinement for 4MPHB. Identification code Empirical formula Formula weight Crystal system Space group Unit cell dimensions
SHELXL C6H8N+C7H5O3 231.24 Monoclinic P21/c a = 7.479 (5) Å b = 11.671 (4) Å c = 13.520 (5) Å a = c = 90°, b = 100.217 (5)° 1161.4 (10) Å3 4, 1.322 488 0.24 0.20 0.18 295 Mo Ka (0.71073) 2.3–27.1° 1939 0.043, 0.128, 1.06
Volume (V) Z, D (calc) (g/cm3) F (0 0 0) Crystal size (mm) Temperature (K) Radiation (Å) Theta Min–Max (Deg) Observed data [I > 2.0 sigma (I)] R, wR2, S
hydrogen bond geometry is shown in Table 2. In the 4MPHB molecular structure (Fig. 3), the H atom between O1 and N1 is disordered over two sites with associated site occupancy of 0.73 (4) and 0.27 (4) respectively. The appearance of H atom near O1 and N1 is clearly identified and fixed subsequently from the different element density map. The same type of positional disorder was already observed in 4,40 -bipyridyl-tartaric acid structure [11]. In the supramolecular arrangement of molecules in 4MPHB crystal, the 4-hydroxy benzoate molecules are linked through O3AH3A O2 hydrogen bonds to form a molecular chain. Due to the presence of disordered hydrogen atom between the O1 and N1 atoms, 73% of 4-methylpyridine molecules are linked through O1AH1A N1 hydrogen bond (Fig. 4a), whereas 27% of the 4methylpyridinium ion are linked through N1AH1A O1 hydrogen bonds (Fig. 4b) in the supramolecular arrangement. The adjacent molecular chains are linked through strong CAH O hydrogen bonds. A R22(8) ring formed by C6AH6. . .O3 connects the adjacent molecular chains, which along with other CAH O hydrogen bonds generates a three dimensional molecular network in the crystalline solid. Even though the compound crystallizes in centrosymmetric space group P21/c, the partial (unequal) transfer of H from O1 to N1 causes a partial difference in the supramolecular arrangement of the crystalline solid. This partial protonation leads charge distortion and it is responsible for the presence of SHG activity in the present system. It concludes that the SHG generation of the crystal is due to charge distribution at the molecular level of supramolecular structures. The experimental details of the SHG in the crystalline solid are discussed in the Section 3.8. Powder X-ray diffraction analysis was performed to confirm the crystallinity and also to estimate the lattice parameters. The sample was scanned over the range of 10–70° at a scan rate of 1 °/min. The powder Xray diffraction pattern of 4-methylpyridinium 4-hydroxybenzoate crystal is shown in Fig. 5.
Table 2 Hydrogen-bond geometry (Å, °). D—H A
d (D—H)
d (HA)
d (DA)
