Corresponding author: R. Mohan Kumar ( mohan66@hotmail.com ) © 2018 Shanmugam Suresh, M. Nizam Mohideen, G. Vinitha, R. Mohan Kumar.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Suresh S, Mohideen MN, Vinitha G, Kumar RM (2018) Synthesis, growth, structural, optical and electrical properties of novel organic single crystal: p-toluidinium salicylate. Modern Electronic Materials 4(3): 103-111. https://doi.org/10.3897/j.moem.4.3.33282
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A novel organic single crystal of p-toluidinium salicylate (PTSA) was grown by slow evaporation solution growth technique. The structure of grown crystal was determined from the single crystal X-ray diffraction analysis. The functional groups existing in PTSA crystal were accomplished by using Fourier transform infrared analysis. The optical transparency and band gap energy were estimated by utilizing the UV-Visible spectrum. Photoluminescence spectral studies revealed the photon excitation. The dielectric behavior of PTSA was investigated for different frequencies in a room temperature (308 K) environment. Third-order nonlinear optical susceptibility (χ3) of PTSA crystal was elucidated by Z-scan measurements.
crystal structure, dielectric, AC conductivity and resistivity, Z-scan analysis
In the modern crystal science and technology, organic materials find wide application in telecommunication, optical limiting, optical data storage, ultrafast signal processes [
PTSA was crystallized by slow evaporation process from p-toluidine (LOBA 99%) and salicylic acid (MERCK 99%) taking in equimolar ratio and the chemical reaction scheme of PTSA is illustrated in Fig.
The crystal structure of PTSA was determined by single crystal X-ray diffraction studies. The intensity data were collected using Bruker kappa APEXII single crystal X-ray diffractmeter with a graphite monochromated MoKα radiation (λ = 0.71073 Å) at 293 K [
Crystal data and structure refinement for PTSA crystal.
Crystal data | Structure refinement |
---|---|
Identification code | PTSA |
Empirical formula | C14H14NO3 |
Formula weight | 244.26 |
Temperature | 293(2) K |
Wavelength | 0.71073 Å |
Crystal system, space group | Monoclinic, P21/n |
Unit cell dimensions | a = 14.1940(16) Å, α = 90.00° b = 4.6883(6) Å, β = 90.613(3)° c = 19.684(2) Å, γ = 90.00° |
Volume | 1309.8(3) Å3 |
Z, Calculated density | 4, 1.239 Mg/m3 |
Absorption coefficient | 0.088 mm-1 |
F (000) | 516 |
Crystal size | 0.300 × 0.250 × 0.200 mm |
Theta range for data collection | 2.87 to 25.21 deg. |
Limiting indices | –16 ≤ h ≤ 16, –5 ≤ k ≤ 5, –23 ≤ l ≤ 23 |
Reflections collected / unique | 22018/2354 [R(int) = 0.0556] |
Completeness to theta = 25.21 | 99.5 % |
Absorption correction | Semi-empirical from equivalents |
Refinement method | Full-matrix least-squares on F2 |
Data / restraints / parameters | 2354 / 0 / 166 |
Goodness-of-fit on F2 | 0.951 |
Final R indices [I > 2sigma (I)] | R 1 = 0.0572, wR2 = 0.1687 |
R indices (all data) | R 1 = 0.1094, wR2 = 0.2205 |
Extinction coefficient | 0.032(6) |
Largest diff. peak and hole | 0.377 and –0.302 e. Å–3 |
The molecular structure of atom with labels and displacement ellipsoids are drawn at the 50% probability level. In the anion (O3–H3A…O2), which generates an S(6) ring motif.
The packing of the title compound, viewed extending along the b axis. Intermolecular hydrogen bonds are shows as dashed lines. H atoms not involved in hydrogen bonding have been omitted.
The p-toluidine cation and salicylate anion are essentially planar, having a maximum deviation of 0.001(3) Å for atom C19 and 0.004(4) Å for atom C7, respectively. The dihedral angle between these two planes is about 36.3(2) Å, indicating that they are nearly parallel to each other. The C–N bond distance of NH2 group i.e., N1–C12 is 1.454 (3) Å, which is short for a C–N single bond, but still not quite as contracted as one would expect for a fully established C═N. These bond length features are consistent with amino resonance form as it is commonly found for C–N single bonds involving sp2 hybridized C and N atoms [
In the crystal structure, intra as well as intermolecular hydrogen bonds could be observed. The intra-molecular hydrogen bonds are formed by the H atom of the alcoholic hydroxyl group as the donor and the carboxylic O atom of the carboxylic acid group as the acceptor in the salicylate anion (O3–H3A…O2), which generates an S(6) ring motif [
Atomic coordinates (×104) and equivalent isotropic displacement parameters (A2 × 103) for PTSA crystal.
Atomic coordinates | x | y | z | U (eq) |
---|---|---|---|---|
C(1) | 3396(2) | –1724(6) | 4549(1) | 50(1) |
C(2) | 2633(2) | 22(6) | 4245(1) | 49(1) |
C(3) | 2789(2) | 1533(7) | 3651(2) | 66(1) |
C(4) | 2107(3) | 3307(8) | 3379(2) | 88(1) |
C(5) | 1256(3) | 3536(9) | 3706(3) | 99(1) |
C(6) | 1081(3) | 2052(10) | 4281(2) | 88(1) |
C(7) | 1757(2) | 243(8) | 4554(2) | 63(1) |
C(8) | 6410(3) | 1034(11) | 1410(2) | 106(2) |
C(9) | 6097(2) | 1730(8) | 2121(2) | 68(1) |
C(10) | 6496(2) | 409(9) | 2673(2) | 75(1) |
C(11) | 6217(2) | 975(7) | 3329(2) | 63(1) |
C(12) | 5514(2) | 2931(6) | 3432(1) | 47(1) |
C(13) | 5099(2) | 4316(7) | 2897(2) | 63(1) |
C(14) | 5398(3) | 3688(8) | 2244(2) | 72(1) |
N(1) | 5199(2) | 3432(5) | 4122(1) | 51(1) |
O(1) | 4219(1) | –1574(4) | 4304(1) | 61(1) |
O(2) | 3220(1) | –3261(5) | 5059(1) | 70(1) |
O(3) | 1544(2) | –1240(7) | 5117(1) | 90(1) |
Bond lengths (Å) and angles (deg) for PTSA crystal.
Atomic coordinates | Bond lengths (Å) / angles (deg) | Atomic coordinates | Bond lengths (Å) / angles (deg) |
---|---|---|---|
C(1)–O(2) | 1.262(3) | C(5)–C(6)–C(7) | 120.4(4) |
C(1)–O(1) | 1.270(3) | C(5)–C(6)–H(6) | 119.8 |
C(1)–C(2) | 1.480(4) | C(7)–C(6)–H(6) | 119.8 |
C(2)–C(3) | 1.386(4) | O(3)–C(7)–C(6) | 118.4(3) |
C(2)–C(7) | 1.394(4) | O(3)–C(7)–C(2) | 122.0(3) |
C(3)–C(4) | 1.380(5) | C(6)–C(7)–C(2) | 119.6(3) |
C(4)–C(5) | 1.379(6) | C(9)–C(8)–H(8A) | 109.5 |
C(5)–C(6) | 1.353(6) | C(9)–C(8)–H(8B) | 109.5 |
C(6)–C(7) | 1.385(5) | H(8A)–C(8)–H(8B) | 109.5 |
C(7)–O(3) | 1.346(4) | C(9)–C(8)–H(8C) | 109.5 |
C(8)–C(9) | 1.508(4) | H(8A)–C(8)–H(8C) | 109.5 |
C(9)–C(10) | 1.368(5) | H(8B)–C(8)–H(8C) | 109.5 |
C(9)–C(14) | 1.375(5) | C(10)–C(9)–C(14) | 117.1(3) |
C(10)–C(11) | 1.380(4) | C(10)–C(9)–C(8) | 121.1(4) |
C(11)–C(12) | 1.371(4) | C(14)–C(9)–C(8) | 121.8(4) |
C(12)–C(13) | 1.366(4) | C(9)–C(10)–C(11) | 122.4(3) |
C(12)–N(1) | 1.454(3) | C(9)–C(10)–H(10) | 118.8 |
C(13)–C(14) | 1.389(4) | C(11)–C(10)–H(10) | 118.8 |
O(2)–C(1)–O(1) | 121.6(3) | C(12)–C(11)–C(10) | 118.9(3) |
O(2)–C(1)–C(2) | 119.2(3) | C(12)–C(11)–H(11) | 120.6 |
O(1)–C(1)–C(2) | 119.2(2) | C(10)–C(11)–H(11) | 120.6 |
C(3)–C(2)–C(7) | 118.8(3) | C(13)–C(12)–C(11) | 120.9(3) |
C(3)–C(2)–C(1) | 120.1(3) | C(13)–C(12)–N(1) | 120.6(3) |
C(7)–C(2)–C(1) | 121.1(3) | C(11)–C(12)–N(1) | 118.5(2) |
C(2)–C(3)–C(4) | 121.2(3) | C(12)–C(13)–C(14) | 118.6(3) |
C(2)–C(3)–H(3) | 119.4 | C(12)–C(13)–H(13) | 120.7 |
C(4)–C(3)–H(3) | 119.4 | C(14)–C(13)–H(13) | 120.7 |
C(5)–C(4)–C(3) | 118.6(4) | C(9)–C(14)–C(13) | 122.2(3) |
C(5)–C(4)–H(4) | 120.7 | C(9)–C(14)–H(14) | 118.9 |
C(3)–C(4)–H(4) | 120.7 | C(13)–C(14)–H(14) | 118.9 |
C(6)–C(5)–C(4) | 121.4(4) | C(12)–N(1)–H(1A) | 120.0 |
C(6)–C(5)–H(5) | 119.3 | C(12)-N(1)-H(1B) | 120.0 |
C(4)–C(5)–H(5) | 119.3 | H(1A)-N(1)-H(1B) | 120.0 |
C(7)-O(3)-H(3A) | 109.5 |
Torsion angles (deg) for PTSA crystal.
Atomic coordinates | Torsion angles (deg) |
---|---|
O(2)–C(1)–C(2)–C(3) | –174.5(3) |
O(1)–C(1)–C(2)–C(3) | 7.6(4) |
O(2)–C(1)–C(2)–C(7) | 7.2(4) |
O(1)–C(1)–C(2)–C(7) | –170.7(3) |
C(7)–C(2)–C(3)–C(4) | 2.2(5) |
C(1)–C(2)–C(3)–C(4) | –176.2(3) |
C(2)–C(3)–C(4)–C(5) | –0.5(5) |
C(3)–C(4)–C(5)–C(6) | –0.4(6) |
C(4)–C(5)–C(6)–C(7) | –0.3(7) |
C(5)–C(6)–C(7)–O(3) | –178.5(4) |
C(5)–C(6)–C(7)–C(2) | 1.9(6) |
C(3)–C(2)–C(7)–O(3) | 177.6(3) |
C(1)–C(2)–C(7)–O(3) | –4.1(5) |
C(3)–C(2)–C(7)–C(6) | –2.8(5) |
C(1)–C(2)–C(7)–C(6) | 175.5(3) |
C(14)–C(9)–C(10)–C(11) | 0.2(5) |
C(8)–C(9)–C(10)–C(11) | –179.2(3) |
C(9)–C(10)–C(11)–C(12) | 0.1(5) |
C(10)–C(11)–C(12)–C(13) | –0.4(5) |
C(10)–C(11)–C(12)–N(1) | 177.6(3) |
C(11)–C(12)–C(13)–C(14) | 0.4(5) |
N(1)–C(12)–C(13)–C(14) | –177.5(3) |
C(10)–C(9)–C(14)–C(13) | –0.2(5) |
C(8)–C(9)–C(14)–C(13) | 179.2(3) |
C(12)–C(13)–C(14)–C(9) | –0.1(5) |
Anisotropic displacement parameters (A2 × 103) for PTSA crystal.
Atomic coordinates | U 11 | U 22 | U 33 | U 23 | U 13 | U 12 |
---|---|---|---|---|---|---|
C(1) | 57(2) | 43(2) | 50(2) | –4(1) | –2(1) | –3(1) |
C(2) | 52(2) | 43(2) | 51(2) | –5(1) | –6(1) | 0(1) |
C(3) | 74(2) | 59(2) | 64(2) | 7(2) | –14(2) | –8(2) |
C(4) | 103(3) | 70(3) | 91(3) | 24(2) | –37(2) | –10(2) |
C(5) | 79(3) | 79(3) | 138(4) | 5(3) | –41(3) | 15(2) |
C(6) | 61(2) | 92(3) | 112(3) | –8(3) | –12(2) | 16(2) |
C(7) | 60(2) | 66(2) | 64(2) | –10(2) | –5(2) | 1(2) |
C(8) | 120(3) | 132(4) | 67(2) | –25(2) | 28(2) | –41(3) |
C(9) | 71(2) | 74(2) | 58(2) | –13(2) | 14(2) | –26(2) |
C(10) | 65(2) | 85(3) | 74(2) | –14(2) | 17(2) | 9(2) |
C(11) | 58(2) | 67(2) | 63(2) | 0(2) | 2(1) | 13(2) |
C(12) | 46(2) | 45(2) | 49(2) | –1(1) | 1(1) | –4(1) |
C(13) | 72(2) | 58(2) | 59(2) | 6(2) | –5(2) | 7(2) |
C(14) | 89(2) | 73(2) | 54(2) | 7(2) | –7(2) | –10(2) |
N(1) | 55(1) | 52(2) | 47(1) | 2(1) | 2(1) | 13(1) |
O(1) | 55(1) | 50(1) | 78(2) | 2(1) | 9(1) | 5(1) |
O(2) | 64(1) | 82(2) | 64(1) | 20(1) | –8(1) | –7(1) |
O(3) | 71(2) | 124(3) | 76(2) | 4(2) | 16(1) | 2(2) |
Hydrogen coordinates (×104) and isotropic displacement parameters (A2 × 103) for PTSA crystal.
Hydrogen coordinates | x | y | z | U (eq) |
---|---|---|---|---|
H(3) | 3364 | 1349 | 3433 | 79 |
H(4) | 2219 | 4327 | 2982 | 106 |
H(5) | 794 | 4735 | 3529 | 119 |
H(6) | 503 | 2249 | 4493 | 106 |
H(8A) | 6104 | 2298 | 1094 | 159 |
H(8B) | 6244 | -901 | 1304 | 159 |
H(8C) | 7080 | 1262 | 1381 | 159 |
H(10) | 6972 | -919 | 2604 | 90 |
H(11) | 6501 | 46 | 3695 | 75 |
H(13) | 4625 | 5650 | 2968 | 76 |
H(14) | 5117 | 4622 | 1878 | 86 |
H(1A) | 4747 | 4608 | 4196 | 62 |
H(1B) | 5465 | 2551 | 4456 | 62 |
H(3A) | 1989 | -2270 | 5222 | 135 |
Hydrogen bonds for PTSA (Å and deg) crystal.
D–H...A | d (D–H) | d (H...A) | d (D...A) | <(DHA) |
---|---|---|---|---|
O(3)–H(3A)...O(2) | 0.82 | 1.84 | 2.564(3) | 146.6 |
N(1)–H(1A)...O(1)#1 | 0.86 | 1.95 | 2.749(3) | 153.4 |
N(1)–H(1B)...O(1)#2 | 0.86 | 2.52 | 3.315(3) | 154.2 |
N(1)–H(1B)...O(2)#2 | 0.86 | 2.12 | 2.751(3) | 130.4 |
The FTIR spectrum of PTSA crystal was recorded in the range 4000 – 400 cm-1 by using KBr pellet technique and the presence of various functional groups in the grown PTSA has been elucidated as shown in Fig.
FT-IR spectral assignment of PTSA crystal.
Wavenumber (cm–1) | Assignments |
---|---|
3496 | Amino N–H asymmetric stretching (NH3+) |
3354 | Amino N–H symmetric stretching (NH3+) |
2849 | C–H stretching medium |
2927 | Methyl C–H symmetric stretching (CH3) |
2552 | Carboxylic acid C=O and O–H stretch |
1429 | Methyl C–H asymmetric bending |
1751 | Aromatic ring C=C stretch |
1919 | C=N stretching vibration |
910 | Stretching of C–C |
613 | Wagging of COO− |
UV-Vis spectral analysis provides an essential structural knowledge due to UV and visible light absorption and it is also associated with the shifting of the electrons from the ground to the higher energy states of π- and σ-orbitals [
where T is the transmittance and ‘t’ is the thickness of the crystal. The optical band gap was estimated from the transmission spectrum and the optical absorption coefficient (α) near the absorption edge was calculated using the relation,
(αhν)2 = A (Eg – hν), (2)
where Eg is the optical band gap of the crystal and A is a constant. The variation of (αhν)2 with ‘hν’ in the fundamental absorption region was plotted as shown in Fig.
Photoluminescence (PL) spectral investigation is one of the most competent mechanisms which impart comparatively direct knowledge regarding the materials’ physical properties at the molecular level, which also includes the defects in deep and shallow level mechanisms and energy gap states. The emission occurs because of the radioactive recombination of electron and hole pair, that is specially necessary for the mechanism of laser in the visible range and it is meant for chromophores in the case of organic crystals [
Dielectric properties are correlated with the electro-optic property of the crystals [
tan δ= εrD (4)
where C is the capacitance, t is the thickness of the crystal, ε0 is the permittivity of free space, D is the dissipation factor and A is the area of the crystal. The variation of dielectric constant as a function of frequency at room temperature is shown in Fig.
The effect of frequency and temperature on AC conductivity offers a lot of information about the bound electric charge carriers. This leads to good explanation and understanding of the electric behavior of organic semiconductors [
σac = 2πfε0εrtan δ, (5)
where, f is the frequency of applied field. The plot of AC conductivity versus frequency at room temperature is shown in Fig.
ρ = 1/2πfε0εrtan δ, (6)
where, ρ is the resistivity and ω is angular frequency of applied electric field. However, the electrical conductivity varied in the opposite direction of resistivity. The PTSA single crystal showed good optical quality with lesser defects and it suggests that the PTSA crystal will be useful for device applications.
The third order nonlinear optical characteristics of PTSA were accomplished by means of the process of Z-scan. This approach facilitates the concurrent measurement of magnitude as well as sign of the nonlinear refractive index (n2) and the nonlinear absorption (β) using the open and closed configurations of Z-scan. In the present investigation, Nd–YAG laser was used to assess the third order nonlinearity of PTSA.
From the obtained data of Z-scan, the difference between the normalized valley and peak transmittance ΔTp-v can be evaluated by using the relation,
ΔTp-v = 0.406(1-S)0.25|φ|, (7)
where, |φ| signifies the on-axis phase shift at the focus and S denotes the aperture linear transmittance, which can be estimated using the relation,
where ra indicates the aperture radius and ωa represents the radius at the aperture.
The on-axis phase shift |φ| is given by,
|φ| = kn2LeffI0, (9)
where Leff = (1 – e–αL)/α, L stands for the length of the used sample, I0 denotes the laser intensity at focus z = 0, α indicates the linear absorption coefficient and k is the wave number (k = 2π/λ).
The nonlinear absorption is reckoned by utilizing the data obtained from the open aperture Z-scan and is given by,
ΔT is the maximum value of the open aperture normalized transmittance obtained from the Z-scan plot. The nonlinear absorption coefficient (β) exhibits a negative value for saturation absorption and positive in the case of two photon absorption. The real and imaginary part of nonlinear optical susceptibility (χ3) were evaluated from the experiment data of ‘n2’and ‘β’ values.
where, ε0 denotes the vacuum permittivity and C represents the velocity of light in vacuum. The absolute third order nonlinear optical susceptibility |χ (3)| is given by
it is observed that the closed aperture Z-scan curve of PTSA discloses the peak to valley configuration as well as it is an evidence for negative nonlinearity as illustrated in Fig.
Third order nonlinear optical parameters of PTSA crystal.
Nonlinear parameters | Measured values |
---|---|
Nonlinear refractive index (n2) | 9.39 × 10–8 cm2/W |
Nonlinear absorption coefficient (β) | 0.02 × 10–4 cm/W |
Real susceptibility (χR(3)) | 10.13 × 10–6 esu |
Imaginary susceptibility (χI(3)) | 0.12 × 10–6 esu |
Absolute susceptibility (χ(3)) | 10.13 × 10–6 esu |
Comparison of χ(3) values of PTSA with other NLO materials.
Crystal | Third order susceptibility χ(3) (esu) | Reference |
---|---|---|
PTSA | 10.13 × 10–6 | Present Work |
LAPA | 5.24 × 10–7 | [28] |
VMST | 9.69 × 10–12 | [29] |
GUCN | 2.05 × 10–8 | [30] |
A novel organic material p-toluidinium salicylate was synthesized and single crystal of PTSA was grown by slow evaporation method. The molecular structure was analyzed by using single crystal X-ray diffraction studies. The single crystal data indicates that the PTSA crystallizes in monoclinic crystal system with centro-symmetric space group P21/n. The existence of diverse functional groups was identified from the FTIR spectral studies. The transmittance in the visible region had the lower cutoff wavelength of 320 nm and the band gap energy of PTSA was estimated to be 3.2 eV. The photoluminescence spectral study disclosed the electron excitation of PTSA. The dielectric constant and dielectric loss of PTSA crystal were studied with different frequency at room temperature. The nonlinear optical parameters were evaluated by closed and open Z-scan signature technique. Thus, the various characterization of PTSA crystal proved its suitability for the future photonic and optoelectronic device fabrication.