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Growth Aspects, Structural, Thermal and Optical
Properties of an Organic Single Crystal:
4-(Dimethylamino)Pyridinium 4-Amino Benzonate
Dihydrate
A Thirunavukkarsu, T Sujatha, P R Umarani, A Chitra, R Mohan Kumar
To cite this version:
Growth Aspects, Structural, Thermal and Optical Propertiesof an Organic
Single Crystal: 4-(Dimethylamino)Pyridinium 4-Amino Benzonate Dihydrate
70A. Thirunavukkarsu1,3, T. Sujatha1, P.R. Umarani2,3, A. Chitra1, R. Mohan Kumar3, a
1 – Department of Physics, S.I.V.E.T College, Chennai-600073, India 2 – Directorate of Collegiate Education, Chennai-600006, India 3 – Department of Physics, Presidency College, Chennai-600005, India a – [email protected]
DOI 10.2412/mmse.5.65.404 provided by Seo4U.link
Keywords: Z-scan technique, X-ray diffraction, photoluminescence, mechanical properties, optical properties.
ABSTRACT. 4-(dimethylamino) pyridinium 4-aminobenzoate dihydrate (DMAPAB) single crystal was grown by
employing the solution growth technique.The grown crystal was characterized by using single X-ray diffraction analysis and found that the title compound crystallizes in triclinic space group P1.From the FT-IR spectral analysis, the presence of functional groups of synthesized compound was identified. The transmission spectrum of DMAPAB crystal showed no absorption in the visible region. The fluorescence spectra of the title compound were analyzedto evaluate the excitation states. The thermal stability and decomposition stages of DMAPAB were elucidated from the TGA-DTA studies.Z-scan technique was employed to determine the third-order nonlinearity of grown crystal.
Introduction. The development of nonlinear opticalmaterials has been the subject of numerous
investigations by both theoreticians and experimentalists in recent years due to their potential applications in optical signal processing. In recent years, researchershave shownmuch interest in the pyridine familycrystals due to their wide transparency window, extended thermal stability and high NLO coefficient. There is much interest in organic nonlinear optical crystals due to their potentially high non-linearity and rapid response in electro-optic devices compared to inorganic NLO materials.The organic NLO crystalsplay important role in third harmonic generation (THG), frequency mixing, electro-optic modulation and optical parametric oscillation [1]. Pyridine and benzoic acid mixedanalog NLO crystals are found to show extended optical and physical properties and hence they can be extensively used for molecular engineering application. Recently, DMAPAB possess the medium strength N—H···O andO—H···Ohydrogenbonds connected bythe adjacent anions and cations,involving water molecules into three dimensional framework. In continuation with the zeal of developing new organiccentric crystal,4-(dimethylamino)pyridinium4-aminobenzoate dihydrate (DMAPAB) crystal has been synthesized from aqueous solution. The present investigation deals with the synthesis, growth and characterizationof (dimethylamino)pyridinium 4-aminobenzoate dihydrate single crystal.
Materials and methods. Thestarting materials were of analytical grade reagents andthe synthesis,
growth process were carried out by dissolving 4-Dimethylaminopyridine and 4-aminobenzoic acidin the stoichiometricratio of 1:1 in aqueous solution. Single crystal of 4-(dimethylamino) pyridinium 4-aminobenzoate dihydrate (DMAPAB) was grown by the slow evaporation solution technique. The crystalline precipitate was formed by proton transfer reaction, where a proton can be transferred from the electron donor group of 4-aminobenzoic acid to the electron acceptor group of 4-Dimethylaminopyridine. The saturated solution was keptat 32ºCwith
moisture and dust free environment. The repeated recrystallizationprocess improved the purity of the compound. The high pure synthesised compound was used to grow the bulk crystal by slow evaporation method. The reaction scheme and photograph of grown single crystal of DMAPAB are shown in Fig.1.
Fig. 1. (a) Synthesis scheme and (b) Photograph of DMAPAB crystal.
Experimental. A Bruker Kappa Apex II single crystal X-ray diffractometer with MoKα (λ =
0.71013 Å) radiation was used to measure cell parameters of DMAPAB crystal with a typical cell dimension of about 0.36 x 0.32 x 0.30 mm3. Powder X- ray diffraction pattern of the grown crystal was recorded by using BRUKER AXS CAD 4 with 1.5406 Å CuKαradiation. The vibrational
spectrum was recorded for DMAPAB compound by using FTIR-4100 type spectrometer at a resolution of 4 cm-1 in the range 400-4000 cm-1. UV-Vis transmission region of DMAPABcrystal was ascertained in the range 190-1100 nm by using LABINDIA T90+ UV-Vis spectrophotometer.TG-DTA experiment was carried out by using a NETZSCH STA 409 instrument with a heating rate of 10ºC/min ranging from 30 to 500 ºC. Z-scan technique was employed to determine the third-order nonlinearity of grown crystal by using 632.8 nm He-Ne laser source.
Results and discussion.
X-ray diffraction studies. Single crystal X-ray diffraction analysis shows that the title compound
crystallizes in the triclinic space group P1, with cell parameters of a = 9.3402(7) Å, b = 9.7999 (7) Å, c = 10.2132 (8) Å, α = 65.755 (3)°, β = 69.983 (2)°, γ = 89.212 (3)°, V = 792.08 (10) Å3, and Z = 2
[2]. The sharpness of defined Bragg peaks in the powder X-ray diffraction pattern confirmed its crystallinity.X-ray powder pattern of DMAPAB is shown in Fig.2. The prominent Bragg peaks in the powder X-ray diffraction pattern were indexed. The peak corresponding to (200),(212),(012) planes have maximum intensity counts at 2θ values of20.10, 22.70 and 18.50 respectively. Thestrongest diffractionpeaks revealed the crystalline natureof the title compound.
FT-IR analysis. The infrared spectral analysis is effectively used to understand the chemical bonding
and it provides information about the molecular structure of the synthesized compound. Theformation of charge transfer complex during the acid: baseinteraction of Dimethylaminopyridine with 4-aminobenzoic acid is stronglyevidenced through the realization of important bands ofdonor and acceptor in the resultant spectrum of the complexsaltas shown in Fig.3. The bands observed at 3451and 3350cm−1 may be due to the asymmetric and symmetric stretching modes of primary amine.
A strong broad NH+ stretching band observed at 3241cm−1. The vibrational frequency occurred at 2927and 2875cm-1are due to asymmetry and symmetry stretching vibrations of methylene group. The peaks arose at 2061, 1965 and1877 cm-1are due to aromatic overtones. The absorption peak noted at 1602 cm-1establishes the presence of carbonyl stretching frequency. The band yielded at 981 cm−1 is due toC-N in-plane bending vibration. The broad band observed at 796 cm-1 is due to C-H-N bending
vibration. The peak observed at 623cm−1 is due to the N–H out-of-plane bending [3]. The recorded
Fig. 2. Powder XRD pattern of DMAPAB crystal. Fig. 3. FT-IR spectrum of DMAPAB.
UV-Vis transmission studies. Optical characteristics provide a good way of examining the properties
of crystalline materials. Particularly, measurement of absorption coefficient for various energies gives information about band gap of the material. The recorded UV–Vis–NIR transmittance of DMAPAB is shown in Fig.4.From the UV-visible transmittance analysis, it is clear that the grown crystal exhibit good transparency of about 60% in the visible region with the lower cut-off wavelength 318 nm. The optical band gap (Eg) was evaluated from the transmission spectrum and the optical absorption
coefficient (α) near the absorption edge was evaluated from the relation:
(αhν) = A ( Eg - hν)1/2 (1)
where A is a constant, Eg is the optical band gap, h is the Planck’s constant and ν is the frequency of
the incident photons.
The Tauc’s plot [4] drawn between the product of absorption coefficient and the incident photon energy (αhν)2 with the photon energy (hν) (Fig.5) shows a linear behavior which is considered as evidence for direct transition. The Eg value obtained by extrapolating the curve was found to be
3.63eV. The wide optical band gap of the grown crystal confirms that the crystal possess large transmittance in the visible region.
Fig. 5.Tauc’s plot drawn between (αhν)2 vs photon energy (hν).
Photoluminescence studies
.
Photoluminescence is a contactless, non-destructive method of probing the electronic structure of materials.Fluorescence may be expected generally in molecules that are aromatic or containing multiple conjugated double bond switches for a high degree of resonance stability.The sample was excited at 300 nm and the emission spectrum was measured in the range of 300–650 nm. From the recorded photoluminescence spectrum (Fig.6), it was observed that the material exhibits a high intense emission peak at 350 nm. Hence, the photoluminescence analysis concludes that DMAPAB crystal exhibits violet fluorescence. The maximum intensity which appears at 350 nm is attributed to n-π* transition with N-H and O-H functional group molecules.Thermal analysis. The thermal analysis of DMAPAB was carried out in nitrogen atmosphere and
thermograms of DMAPAB crystal areshown in Fig.7. In TGA, the first weight loss stage observed at 123oC is due to the presence of water molecules in the synthesized salt. It is seen, that the major weight loss started at 214oC and it continued up to 290oC. It indicates that this huge weight loss is
due to the decomposition of functional group molecules in the form of NH and CH3 evaporation. The
synthesized compound DMAPAB has thermal stability upto214oC. In the DTA, the weight loss occurred due to the water molecules; also the sharp endothermic peak observed at 180oC is due to
decomposition or melting point of compound of DMAPAB crystal. The sharpness of endothermic peaks observed in DTA indicates the good degree of crystallinity of the sample.
Fig. 6. PL spectrum of DMAPAB. Fig. 7. TG/DTA thermogram of DMAPAB.
Z-Scan Measurement. The Z-scan study is needed to examine nonlinear opticalbehavior which is
From the Z-scan data, the difference between the valley and peak transmittance (∆Tv-p) was evaluated
in terms of the on-axis phase shift at the focus.
o 25 . 0 p v 0.4061 S T (3)where S is the linear transmittance aperture and it was calculated using the relation,
2 2 2 exp 1 a a r S (4)
where ra is the radius of aperture and ωa is the beam radius at the aperture.
The nonlinear refractive index (n2) was calculated by using closed aperture Z-scan data [6, 7].
eff o o L KI n2 (5)
The third order nonlinear optical susceptibility was calculated using the relation [8],
3
3
2
3
2Im
Re
(6)
The calculated third order nonlinear optical parameters are given in Table 1. Z-scan studies confirm that the DMAPAB crystal can be a promising NLO material for optical device applications such as optical modulators and optical limiters.
Table 1. Optical parameters of DMAPAB measured in Z-scan experiment.
Effective thickness (Leff) 0.9974 mm
Nonlinear refractive index (n2) 0.9584 ×10−10cm2/W
Nonlinear absorption coefficient () 2.4283 ×10−3 cm/W
Fig. 8. Z-scan traces observed in (a) Open aperture and (b) closed aperture modes for DMAPAB Crystal.
Summary. Organic single crystal of DMAPABwas grown by the slow evaporation solution growth
technique. The crystal structure of DMAPABwas determined by single crystal XRD studies. From the UV-Vis spectral analysis, it was found that the DMAPABcrystal istransparent in the entire visible region and the cut-off wavelength was found to be 318 nm. The photoluminescence analysis concludes that DMAPAB crystal exhibits violet fluorescence.Fromthe TG–DTA curve, it is clearly observedthat the synthesised material is stable up to 214 oC. The third order nonlinearoptical susceptibility, nonlinear refractive index and
nonlinearabsorption coefficient were estimated by Z-scan studies.
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A. Thirunavukkarsu, T. Sujatha, P.R. Umarani, A. Chitra, R. Mohan Kumar, (2017). Growth Aspects, Structural, Thermal and Optical Propertiesof an Organic Single Crystal: (Dimethylamino)Pyridinium
4-Amino Benzonate Dihydrate. Mechanics, Materials Science & Engineering, Vol 9. Doi
