Synthesis, structural, spectroscopic, mechanical, linear and nonlinear optical studies on 4-dimethylaminopyridinium p-toluenesulfonate: A comparative theoretical and experimental investigation

Article abstract of DOI:10.1016/j.molstruc.2021.130530

Single crystal of 4-(Dimethylamino)pyridinium p-toluenesulfonate (4DMPT) has been successfully grown by solution growth method and its structural characterization has carried out by X-ray diffraction methods. Single crystal XRD study shows that the grown

Full text of DOI:10.1016/j.molstruc.2021.130530

Journal of Molecular Structure 1240 (2021) 130530
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Synthesis, structural, spectroscopic, mechanical, linear and nonlinear
optical studies on 4-dimethylaminopyridinium p-toluenesulfonate: A
comparative theoretical and experimental investigation
G. Sivaraja,b, N. Jayamani , V. Siva
b,∗
c,d,∗
a
Department of Physics, Periyar University, Salem, 636 011, India
b
c
Department of Physics, Government Arts College, Salem, 636 007, India
Department of Physics, School of Advanced Sciences, Kalasalingam Academy of Research and Education, Krishnankoil, 626 126, India
Condensed Matter Physics Laboratory, International Research Centre, Kalasalingam Academy of Research and Education, Krishnankoil, 626 126, India
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Single crystal of 4-(Dimethylamino)pyridinium p-toluenesulfonate (4DMPT) has been successfully grown
by solution growth method and its structural characterization has carried out by X-ray diffraction meth-
ods. Single crystal XRD study shows that the grown crystal crystallized in the monoclinic system with
unit cell dimensions a = 8.986 (6) A˚, b = 17.591 (5) A˚, c = 9.784 (8) A˚, β = 112.296˚(3), V = 1448.18
Received 3 November 2020
Revised 10 April 2021
Accepted 19 April 2021
Available online 4 May 2021
(
17) A3 and Z = 4. The quantum chemical calculations have been carried out at HF and DFT (B3LYP/
Keywords:
CAMB3LYP/ M06–2X) with 6–311++G(d,p) levels to reach the optimized geometry, charge distributions
and HOMO-LUMO nature. A good correlation is shown between computed and experimental structural
parameters such as bond lengths and bond angles. The load dependent hardness values of the crystal
have been analyzed. The optical spectrum revealed the ultra violet cut-off wavelength at 284 nm. The
third order nonlinear optical responses have been studied by Z-Scan technique. The calculated value of
third order non-linear refractive index (n2), third order non-linear absorption coefficient (β) and third
Organic
Single crystal XRD
Hardness
Nonlinear optics
Quantum chemical calculations
order non-linear optical susceptibility (χ(3)) is 8.18 × 10−8cm /W, 0.20 × 10 cm/W and 12.88 × 10−6
2
−4
esu, respectively.
©
2021 Elsevier B.V. All rights reserved.
1
. Introduction
Pyridinium derivatives are important in synthetic chemistry [4,5].
Among them, amino pyridines are the basic building blocks for
the development of novel functional molecules. Directional hydro-
gen bonding interactions have strong hyperpolarizability; exhibit-
ing non-linear optical properties [6].
Nowadays, enormous efforts have been made to develop new
nonlinear optical (NLO) materials due to their widespread appli-
cation in technologies such as lasers, optoelectronics, frequency
conversion and the optical power limiting of both organic and in-
organic compounds. In organic materials, electrons are more ac-
cessible and NLO-effects arises from the interaction between light
and electrons within individual molecular units, giving quicker re-
sponses [1–3]. As a part novel NLO materials synthesis, more de-
terminations are being made to comprehend the derivation of lin-
earity in large systems and to correlate NLO responses to molec-
ular structure and geometry. Organic compound offers many at-
tractive opportunities in applications which are NLO materials due
to the presence of π-conjugated delocalized electronic structure.
Moreover, organic crystals play a crucial part in the field of
supramolecular chemistry, crystal engineering and also biological
sciences, etc. due to their potential applications in drug deliv-
ery and also nonlinear optics [7]. In addition, the attraction to-
wards organic materials could be owing to ultra-fast nonlinear re-
sponse time, large NLO susceptibilities moreover high laser dam-
age threshold [8,9]. In general, several organic charges transfer
crystal of p-toluenesulfonic acid among the organic acceptor com-
pound revealed in NLO applications. These crystalline materials are
composed of π-conjugated molecules chemical purity that pro-
vides highly ordered structures and a model. To explore the ba-
sic electronic properties of organic semiconductor materials, pyri-
dine and acid are one among promising pairs forming a non-
centrosymmetric crystal arrangement that exhibits high NLO per-
formance [10–12].
∗
Corresponding authors at: Department of Physics, Condensed Matter Physics
Laboratory, International Research Centre, Kalasalingam Academy of Research and
Education, Krishnankoil 626 126, India.
E-mail addresses: drnjayamani@gmail.com (N. Jayamani), siva33phy@gmail.com
(V. Siva).
https://doi.org/10.1016/j.molstruc.2021.130530
022-2860/© 2021 Elsevier B.V. All rights reserved.
0

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Table 1
Comparative representation of bond lengths for 4DMPT.
Bond length ( A˚ )
HF
DFT
EXP
B3LYP
CAMB3LYP
M06-2X
C(1)−C(2)
C(1)−N(1)
C(2)−C(3)
C(3)−C(4)
C(3)−N(2)
C(4)−C(5)
C(5)−N(1)
N(2)−C(6)
N(2)−C(7)
C(10)−C(11)
C(11)−C(12)
C(11)−S(1)
C(9)−C(10)
C(8)−C(9)
C(8)−C(13)
C(8)−C(14)
C(12)−C(13)
S(1)−O(2)
S(1)−O(1)
S(1)−O(3)
1.361
1.331
1.419
1.414
1.343
1.364
1.334
1.455
1.456
1.381
1.387
1.777
1.388
1.387
1.393
1.510
1.381
1.476
1.453
1.433
1.374
1.343
1.422
1.420
1.358
1.375
1.346
1.461
1.461
1.391
1.393
1.804
1.394
1.398
1.400
1.510
1.391
1.529
1.488
1.467
1.368
1.337
1.416
1.414
1.352
1.370
1.341
1.454
1.455
1.441
1.385
1.386
1.789
1.083
1.393
1.394
1.505
1.094
1.457
1.478
1.374
1.343
1.422
1.420
1.358
1.375
1.346
1.461
1.461
1.391
1.393
1.804
1.394
1.398
1.400
1.510
1.391
1.529
1.488
1.467
1.363
1.344
1.425
1.420
1.336
1.359
1.342
1.460
1.461
1.391
1.394
1.774
1.392
1.397
1.382
1.515
1.391
1.472
1.450
1.448
Fig. 1. Photograph of the 4DMPT single crystal.
The development of multi-functionalized compound with at-
tractive physicochemical properties such as ferroelectric, ferro-
magnetic, piezoelectric and NLO properties for practical appli-
cations has become one of the fast growing multi-disciplinary
areas [13]. 2-amino-4-picolinium toluene sulfonate [14], guani-
dinium p-toluenesulfonate [15,16], β-alaninium p-toluenesulfonate
2
.3. Quantum chemical calculations
The quantum computational calculations conducted for the ti-
[
17], l- Alaninium p- toluenesulfonate [18], l- Valinium p- tolue-
nesulfonate monohydrate [19], l- Leucinium p- toluenesulfonate
monohydrate [20] 2-Amino-5-nitropyridinium p-toluenesulfonate
tle compound were performed with the GAUSSIAN 09 W [24] us-
ing the DFT and HF approaches using the crystallographic data.
Initially, we determined the optimized geometry within DFT us-
ing the Becke three parameter hybrid exchange functional and the
Lee-Yang-Parr correlation [25–28], M06–2X and CAMB3LYP hybrid
functions at 6–311++G(d,p) basis set [29–31]. The charge transfer
at molecular level was assessed with a frontier molecular analy-
sis using DFT and HF methods. Finally, the Gauss View 05 [32] was
used to visualize the optimized structure, the three dimensional
HOMO-LUMO images of the title compound.
[
21] and 2-amino 4, 6 dimethoxypyrimidine p-toluenesulfonic acid
monohydrate [22] are some of the p- toluenesulfonate (tosy-
late) based compounds studied systematically for their NLO ac-
tivity were reported previously. In this work, crystal growth,
solid state properties and quantum chemical studies of 4-
(
dimethylamino)pyridinium p-toluenesulfonate are presented and
their results are explained in detail.
2
. Experimental and computational details
2
.1. Synthesis and crystallization
3. Results and discussion
The reactants were commercially purchased (Merck, AR Grade
3
.1. Single crystal XRD analysis
>
99%) and used without further purification. Solution of
4
-Dimethylaminopyridine and p-toluenesulfonic acid(1:1) was
+
.
Single crystal XRD study revealed that 4DMPT (C H11 N2
7
heated to 40 °C and stirred for 2 h before being poured into a petri
dish and kept undisturbed for 18 days. In general, the hydrogen
bonds are non-bonded interactions between a positively charged
hydrogen atom and an electronegative atom with lone electron
pairs and can be adequately modeled by appropriately chosen
atomic charges. From this reaction, the anion (p-toluenesulfonic
acid) and the cation (4-dimethylaminopyridine) form a regular pat-
tern alternating back and forth through charge transfer reaction.
The crystal is held together by electrostatic attraction. Pale yellow
colored single crystals were obtained by the slow evaporation of
a methanol solution. The photograph of the harvested crystal was
shown in Fig. 1.
−
C H O S ) belongs to monoclinic crystal system with space group
7
7
3
P2 /n. The unit cell dimensions were found to be a = 8.986 (6) A˚,
1
b = 17.591 (5) A˚, c = 9.784 (8) A˚, β = 112.296 ˚(3), V = 1448.18
17) A3 and Z = 4. The data obtained were found to be well
(
matched with the reported values [33]. Powder XRD pattern of
4
DMPT was given in supplementary information. The crystal struc-
ture 4DMPT was formed through N–H…O and C–H…O networks of
-dimethylaminopyridine and p-tolunesulfonic acid. Furthermore,
4
N–H…O hydrogen bonds combined as separate pairs of cations and
anions. This structure was further confirmed by the comprehen-
sive series of C–H…O hydrogen bonds, magnified π − π [centroid-
centroid distance between adjacent pyridinium rings = 3.5807 (10)
A˚] and C - H interactions, providing the network configuration.
The structural parameters were available as crystallographic infor-
mation file (CIF) at Cambridge Crystallographic Data Centre (CCDC)
reference number 680683.
2
.2. Characterization technique details
Single crystal X-ray diffraction was used to confirm the unit
cell parameters of the crystal using Bruker AXS KAPPA APEX-
diffractometer fitted with graphite monochromator [23]. The
2
3.2. Molecular geometry
grown crystal was analyzed to understand crystalline nature by
powder XRD study using Bruker D8 advance ECO XRD systems.
The Optical transmittance spectrum was measured in the range of
The structural parameters such as bond length and bond angle
of the 4-dimethylaminopyridinium p-toluenesulfonate compound
are listed in Table 1 & 2. The optimized molecular structures of
title compound are depicted in Fig. 2-5 for HF and DFT (B3LYP/
CAMB3LYP/ M06–2X) with 6–311++G(d,p) levels. The comparison
2
00–1100 nm using the UV-1700 Shimadzu spectrometer. NLO re-
sponse was studied by using a Coherent Compass TM215M-50 with
a wavelength of 532 nm.
2

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Table 2
Comparative representation of bond angles for 4DMPT.
DFT
Bond angle (°)
HF
EXP
B3LYP
CAMB3LYP
M06–2X
C(2)−C(1)−N(1)
C(1)−C(2)−C(3)
C(2)−C(3)−C(4)
C(2)−C(3)−N(2)
C(4)−C(3)−N(2)
C(3)−C(4)−C(5)
C(1)−N(1)−C(5)
C(3)−N(2)−C(6)
C(3)−N(2)−C(7)
C(6)−N(2)−C(7)
C(10)−C(11)−C(12)
C(10)−C(11)−S(1)
C(11)−C(10)−C(9)
C(9)−C(8)−C(13)
C(9)−C(8)−C(14)
C(13)−C(8)−C(14)
C(11)−C(12)−C(13)
C(10)−C(9)−C(8)
C(8)−C(13)−C(12)
C(11)−S(1)−O(2)
C(11)−S(1)−O(1)
C(11)−S(1)−O(3)
O(2)−S(1)−O(1)
O(2)−S(1)−O(3)
O(1)−S(1)−O(3)
122.02
119.47
116.55
121.61
121.84
119.97
120.61
120.51
120.34
119.15
119.96
120.56
119.85
118.32
121.27
120.40
119.78
121.01
121.08
105.48
106.46
106.65
109.26
112.65
115.62
121.83
119.79
116.51
121.66
121.83
120.22
120.35
120.41
120.28
119.31
120.47
120.15
119.49
118.24
121.07
120.67
119.45
121.16
121.20
104.27
106.61
106.81
109.45
112.22
116.56
121.85
119.66
116.68
121.57
121.75
120.12
120.42
120.32
120.19
119.49
120.53
120.12
119.48
118.36
120.92
120.70
119.42
121.08
121.13
106.72
106.61
104.53
116.55
112.38
109.15
121.83
119.79
116.51
121.66
121.83
120.22
120.35
120.41
120.28
119.31
120.47
120.15
119.49
118.24
121.07
120.67
119.45
121.16
121.20
104.27
106.61
106.81
109.45
112.22
116.56
121.48
119.56
116.70
121.33
121.97
120.08
120.78
120.79
120.98
118.20
120.03
119.89
119.64
118.39
122.30
119.30
119.31
120.97
121.65
104.31
106.15
107.29
111.64
114.71
111.92
Fig. 2. Optimized molecular structure of 4DMPT with atom numbering scheme by HF at 6-311++G(d,p) levels.
Fig. 3. Optimized molecular structure of 4DMPT with atom numbering scheme by B3LYP at 6-311++G(d,p) levels.
3

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Fig. 4. Optimized molecular structure of 4DMPT with atom numbering scheme by CAMB3LYP at 6-311++G(d,p) levels.
Fig. 5. Optimized molecular structure of 4DMPT with atom numbering scheme by M06-2X at 6-311++G(d,p) levels.
of bond angles and bond lengths of DFT with HF, showed a good
agreement between the two methods with slightly larger bond
lengths for the DFT values. The bond lengths of the optimized ge-
ometries are slightly higher than the experimental values and this
discrepancy might be due to the fact that the calculations were
performed for an isolated molecule in the gas phase and the effect
of the crystalline environment was not taken into account.
toluenesulfonate are observed at shorter distance in computational
˚
˚
˚
calculation (2.726 A for HF, 2.824 A/ B3LYP, 2.818 A/ CAMB3LYP
˚
and 2.782 A/ M06–2X for DFT methods) than the solid crystalline
˚
state (2.716 (3) A), which is the confirmation for the dipole–dipole
interaction among these two ion pairs. This result shows that the
N–H•••O intermolecular hydrogen bonding effect is supposed to
be more between the ions in computational than solid crystalline
state.
The pyridine ring had two C=C bonds C(1)=C(2)=1.3606 A
˚
˚ ˚ ˚ ˚
1.374 A (HF/DFT) and 1.363 A (EXP), C(4) C(5) 1.3641 A /1.3751 A
=
/
(
˚
–
A (EXP). And two C C single bonds
HF/ B3LYP) and 1.359
˚
3
.3. Frontier molecular orbitals (FMO) analysis
˚
˚
C(2)−C(3)= 1.4188 A / 1.422 A and 1.425 A (EXP), C(3)−C(4)=
˚ ˚ ˚
.4143 A / 1.4199 A and 1.42 A [34], this result showed that the
1
In FMO analysis, HOMO (Highest Occupied Molecular Orbital)
theoretical values were in good agreement with the experimental
values.
and LUMO (Lowest Unoccupied Molecular Orbital) was very im-
portant to predict chemical stability. [37,38]. In order to evaluate
the energetic behavior, we performed calculations on the gas phase
HOMO and LUMO energy gaps calculated are presented in Table 3.
The 3-D plots of the frontier orbitals shown in Fig. 6 (HF & B3LYP)
and Fig. 7 (CAMB3LYP & M06–2X levels). The positive phase was
red and the negative phase in green. These figures showed the
electron density plot for the most important FMOs of the energy
in a.u and the energy gap in the eV. The calculated energy val-
ues of HOMO = −0.3105 a.u (HF)/−0.2282 a.u (B3LYP)/ −0.2827
a.u (CAMB3LYP) /−0.2282 a.u (M06–2X) and LUMO = 0.0137 a.u
The optimized bond length of the C–N is observed and were
˚
˚
in range of ~1.331 A to ~1.461 A in HF and DFT method whereas
the single crystal XRD revealed that the C–N bond lengths between
˚
˚
the range ~1.344 A and ~1.461 A [35,36]. The experimental results
were in good agreement with the theoretical values, as it can be
observed in the plots of the theoretical versus experimental geo-
metrical parameters (given in supplementary information). The cal-
culation provide good agreement between the theoretical and ex-
perimental bond length values except C–H and N–H bond lengths;
because the calculated HF and DFT values of C–H and N–H bond
lengths are lower than experimental values.
(
(
HF)/ −0.0692 a.u (B3LYP)/ −0.0220 a.u (CAMB3LYP) / −0.0692 a.u
M06–2X), the energy gap ࢞E= (E -E ) = 8.82 eV (HF)/
HOMO LUMO
The intermolecular N–H…O hydrogen bond, the Nitrogen atom
of the 4-dimethylaminopyridine and Oxygen atom of the p-
4
.33 eV (B3LYP)/ 7.1028 (CAMB3LYP) and 4.3319 (M06–2X), respec-
tively. The energy gap (࢞E) was an essential parameter as a func-
4

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Fig. 6. Frontier molecular orbitals by HF and DFT/B3LYP levels.
tion of the reactivity of the molecule. A molecule with a low en-
ergy gap was highly polarizable and was generally related with
high chemical activity and low chemical stability and is called a
soft molecule. According to Koopman’s theorem [39], the energies
of the HOMO and the LUMO were assigned to the ionization poten-
tial (I), and the electron affinity (A), respectively, by the following
relations:
Ionization potential (I) = −EHOMO
Electron affinity (A) = −ELUMO
Electronegativity (χ) = {(I + A)/2}
(1)
(2)
Global Hardness(η) = {(I − A)/2}
5

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Fig. 7. Frontier molecular orbitals by DFT/CAMB3LYP and M06-2X levels.
molecules is often due to intra-molecular charge transfer character
of FMOs and lower energy transitions which can be easily charac-
terized by any reasonable calculation technique like DFT etc. [40].
ꢀ
ꢁ
2
Global electrophilicity(ω) = μ /2η
(3)
High ionization energy refers to high stability and chemical in-
ertness and small ionization refers to the high reactivity of energy
molecules. Absolute hardness and softness are important proper-
ties to measure molecular stability and reactivity. The chemical
hardness refers to the resistance to decay or polarization of an
electron cloud of atoms, ions, or molecules under the slightest
disturbance of a chemical reaction. The NLO response of organic
3.4. Mulliken population analysis
In Mulliken’s charge analysis, each of the contributing orbitals
was assigned to one another, giving the total population of each
atomic orbital. Summarizing the total number of atomic orbits in
a given atom was the gross atomic population [35]. The sum of
6

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Fig. 8. Mulliken charge distributions for 4DMPT by HF and DFT/B3LYP levels.
Table 3
maximum negative charge value of about −0.7710(HF)/−0.7515
B3LYP)/ −0.7405 (CAMB3LYP) / −0.9674 (M06–2X) because charge
transferred from N(2) within the molecule. The C8 (0.4842 /HF,
.5733/B3LYP, 0.5563 in CAMB3LYP) atom which was attached to
Molecular orbital energy values of 4DMPT.
(
Energy
Molecular
0
DFT
Properties
HF
the functional group (CH ) experienced a high positive charge, and
3
B3LYP
CAMB3LYP
M06-2X
were due to the presence of the electronegative atom, that with-
draw electrons from the C atoms of the ring. All the hydrogen
atoms were positive [37]. Moreover Mulliken charges showed that
the H(1) atom (charge 0.7925 in HF, 0.7328 in B3LYP, 0.7113 in
CAMB3LYP and 0.6370 for M06–2X) is more positive than others
that is due to the hydrogen atom being surrounded by the two
electronegative atoms nitrogen N(1) and oxygen O(2).
HOMO
LUMO
−0.3105
0.0137
0.3241
8.8296
0.3105
−0.0137
0.1621
6.1704
0.1484
−0.1484
0.0679
−0.2282
−0.0692
0.1590
4.3310
0.2282
0.0692
0.0795
12.5794
0.1487
−0.1487
0.1390
−0.2827
−0.0220
0.2607
7.1028
0.2827
0.0220
0.1304
7.6705
0.1523
−0.1523
0.0890
−0.2282
−0.0692
0.1590
4.3319
0.2282
0.0692
0.0795
12.5770
0.1487
−0.1487
0.1390
ꢀ
ꢀ
(EHOMO-ELUMO) a.u
(EHOMO-ELUMO) eV
Ionization Potential (I)
Electron Affinity (A)
Global Hardness (η)
Global Softness (ʋ)
Electro negativity(χ)
Chemical potential (μ)
Global Electrophilicity (ω)
3
.5. Mechanical stability analysis
Hardness is one of the important mechanical properties of the
materials. As the hardness of the crystal determines the mechani-
cal stability of the crystal, it was an inevitable parameter to be de-
termined [42]. The Vicker’s micro hardness polished crystals were
placed on the tester’s platform and fixed indentations were made
using the Leitz Wetzlar Vicker’s microhardness on a smooth (0 0
all net and mutual populations equals the total number of elec-
trons in the molecule. The charge distribution on the molecule
had a major influence on the vibration spectrum, dipole mo-
ment, polarization and electronic structure [41]. The Mulliken’s
atomic charge values were presented in Table 4 and the graph-
ical representation was given in Figs. 8& 9. It was essential to
mention that C(2), C(5) and C(8) atoms of title compound ex-
hibit positive charges (except M06–2X), while C(1), C(3), C(4),
C(6), C(7), C(11), C(10), C(12), C(9), C(13) and C(14) atoms ex-
hibit negative charges. The C(3) atom of title compound had a
1
) face with a constant indentation time of 10 s. Hardness number
(
Hv) was determined by the relation,
ꢀ
ꢁ
2
2
Hv = 1.8544 P/d kg/mm
(4)
Where P is the load and d is the average diagonal length of the
indentation.
7

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Fig. 9. Mulliken charge distributions for 4DMPT by DFT/CAMB3LYP and M06-2X levels.
Fig. 10. (a) Hardness Number (HV) vs Load (P), (b) Variation of log P with log d.
8

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Table 4
Atomic charges of 4DMPT.
DFT
Atom
HF
B3LYP
CAMB3LYP
M06-2X
C(1)
−0.3541
0.5128
−0.7710
−0.3574
0.1957
−0.4209
−0.0486
−0.2696
−0.3350
−0.6946
−0.1833
0.4842
0.0015
−0.6965
−0.1153
−0.5040
0.5866
−0.4238
−0.5278
−0.2767
0.2119
0.2601
0.2529
0.3497
0.1634
0.1605
0.1635
0.1502
0.1678
0.1710
0.2550
0.2664
0.1857
0.2000
0.1433
0.1440
0.1599
0.7925
−0.3739
0.5040
−0.7515
−0.2467
0.0937
−0.2430
0.0132
−0.2976
−0.3440
−0.3378
−0.2049
0.5733
−0.0806
−0.5337
−0.2879
−0.4711
0.0733
−0.2905
−0.3816
−0.1522
0.1621
0.2146
0.2138
0.2593
0.1526
0.1663
0.1693
0.1439
0.1732
0.1753
0.1946
0.2192
0.1521
0.1599
0.1413
0.1427
0.1664
0.7328
−0.2886
0.3905
−0.7405
−0.2259
0.0970
−0.2380
0.0091
−0.3128
−0.3505
−0.3251
−0.2398
0.5563
−0.1016
−0.5053
−0.3336
−0.4458
0.1915
−0.4165
−0.1824
−0.3181
0.1745
0.2210
0.2223
0.2626
0.1537
0.1653
0.1691
0.1457
0.1752
0.1717
0.1973
0.2295
0.1652
0.1670
0.1403
0.1393
0.1690
0.7113
−0.6167
0.8188
C(2)
C(3)
−0.9674
−0.1865
−0.1998
−0.1398
0.1096
C(4)
C(5)
N(1)
N(2)
C(6)
−0.3559
−0.4258
−0.2636
−0.3378
0.6185
C(7)
C(11)
C(10)
C(8)
C(12)
C(9)
−0.1056
−0.6182
−0.4482
−0.5292
0.3857
C(13)
C(14)
S(1)
O(2)
−0.2162
−0.2589
−0.1178
0.1636
Fig. 11. Optical absorbance spectrum.
O(1)
O(3)
Table 5
Measurement details of Z- Scan setup and calculated NLO parameters.
H(2)
H(3)
0.2314
H(4)
0.2102
Parameters
Values
H(5)
0.2476
Laser beam wavelength(λ)
Focal length of the lens
632.8 nm
30 mm
85 cm
H(6A)
H(6B)
H(6C)
H(7A)
H(7C)
H(7B)
H(7)
0.1688
0.1718
Optical path length
0.1760
Beam radius of the aperture (Wa)
Aperture radius (ra)
3.3 mm
2 mm
0.1532
0.1809
Sample thickness (l)
0.6 mm
12 μm
4.38 KW/cm2
0.47 mm
0.777
0.1872
Beam radius (W0)
0.1385
Incident intensity at the focus (Z = 0)
Effective thickness (L eff)
H(8)
0.2646
H(6)
0.2087
Linear absorption coefficient (α)
Linear transmittance (S)
H(9)
0.2015
0.15
H(14A)
H(14B)
H(14C)
H(1)
0.1597
−
8
2
Nonlinear refractive index (n2)
Non linear absorption coefficient (β)
Third order nonlinear susceptibility (χ(3)
8.18 × 10 cm /W
0.1637
−4
0.20 × 10 cm/W
0.1903
−6
)
12.88
×
10 esu
0.6370
real and imaginary parts of the third order Non-linear optical sus-
ceptibility χ(3) were defined as
Fig. 10(a) showed loads with different hardness numbers and
differs in that the hardness value increases with increasing load
Re χ = (10−4 × ε c n n2)/π
(
3)
2
2
(5)
(6)
[
43]. When the load reaches a maximum value of 100 g, the har-
0
0
2
ness was found to be 43.91 kg/mm , which was found to increase
the stiffness with the load. Fig. 10(b) illustrated the variation of
log P with log d. The value of Meyer’s index ‘n’ is determined from
the slope of log d versus log P plot. The calculated value was 3.32,
which showed the grown crystal was a soft material.
ꢀ
ꢁ
Im χ = (10−2 × ε0c n0 λβ)/ 4π
(
3)
2
2
2
where ε0 is the vacuum permittivity, n is the linear refractive in-
0
dex of the sample and c is the velocity of light in vacuum. The
absolute value of the third order Non-linear optical susceptibility
χ(3) was calculated from the formula
3
.6. Linear and nonlinear optical analysis
ꢂ
ꢃ
ꢀ
ꢁ
ꢀ
ꢁ
1/2
2
2
(
3)
(3)
(3)
In the UV–vis region, high transmittance had significant appli-
χ
=
Re χ
+ Im χ
(7)
cations for laser threshold and optoelectronic devices. The grown
crystal optical absorption spectrum was recorded in the range
of 200–800 nm (Fig. 11). Absorption of organic compounds was
The calculated value of third order non-linear refractive index
(n ), third order non-linear absorption coefficient (β) and the third
2
∗
(3)
−8
2
caused by the transitions of π electrons to the π excited state.
order non-linear optical susceptibility (χ ) is 8.18 × 10 cm /W,
−
4
−6
These electron transitions must be attributed to the molecular
π-electrons [44]. Therefore, this transition created an absorption
band over long wavelengths. The lower cut-off wavelength in
grown crystal was around 298 nm in UV–Vis spectrum and had
no absorption in the visible regions. This broad transparency indi-
cated the grown crystal have the potential for a variety of optical
applications [45,46].
0.20 × 10 cm/W and 12.88 × 10 esu, respectively.
The measurement details of Z- Scan setup and calculated NLO
parameters were given in Table 5. The decrease in normalized
transmittance with the input intensity suggested that reverse sat-
uration absorption was the leading mechanism behind non-linear
absorption in crystals. According to these results, to achieve sat-
urated absorption, low intensity energy levels must be filled up
to the level of photon excitation [49,50]. The results of the ti-
tle compound have been compared with some of the reported p-
toluenesulfonate crystals and are presented in Table 6. It suggests
that the grown crystal possess higher (χ(3)) value than the re-
ported p-toluenesulfonate materials. With the above characteris-
Third order nonlinear optical parameters were analyzed on
4
DMPT crystal using Z-scan technique with a length of diffraction
of 1.48 mm [47,48]. Third order nonlinear parameters such as re-
fractive index (n ), absorption coefficient (β) and third-order NLO
2
3
susceptibility (χ ) of crystal was studied by Z-scan technique. The
9

G. Sivaraj, N. Jayamani and V. Siva
Journal of Molecular Structure 1240 (2021) 130530
Table 6
Comparison of nonlinear absorption coefficient and nonlinear optical susceptibility with some of the
p-toluenesulfonate crystals.
Material
Third order nonlinear
absorption coefficient
Third order nonlinear
susceptibility χ(3)(esu)
Ref.
(
β) (cm/W)
4
3.38 × 10−6
2.74 × 10−6
7.372 × 10−11
3.143 × 10−4
2
-amino-4-picolinium toluene −7.7 × 10−
[14]
[16]
[17]
[21]
sulfonate
4
Guanidinium
0.08 × 10−
p-toluenesulfonate
β-alanininium
p-toluenesulfonate
2.329 × 10−
2
2
2
-amino 4, 6 dimethoxy
0.311 × 10−
pyrimidine
p-toluenesulfonic acid
monohydrate
0.20 × 10−
4
12.88 × 10−6
Present work
4
-dimethylaminopyridium
p-tolunesulfonate
tics, title compound can be declared as an excellent candidate for
optoelectronic device applications.
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Optically good quality single crystals of 4DMPT were success-
1
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[
a
Declaration of Competing Interest
4
[
12] M. Odabas¸oglu, O. Buyukgungor, G. Turgut, A. Karada € g, E. Bulak, P.L. on-
necke, Crystal structure, spectral and thermal properties of 2-aminopyridinium
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None.
1
016/S0022-2860(02)00720-2.
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CRediT authorship contribution statement
[
15] Paavai Era, RoMu Jauhar, P. Vivek, P. Murugakoothan, Investigation on the
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