Growth and characterization of anilinium hydrogen sulfate (AHS) single crystals: An organic nonlinear optical material

Article abstract of DOI:10.1016/j.saa.2012.07.048

Single crystals of anilinium hydrogen sulfate (C₆H ₈N⁺·HSO4-, AHS) have been grown by slow evaporation solution growth technique using water as a solvent. Powder X-ray diffraction (XRD) study has been carried out to determine the lattice parameters. Fourier transform infrared (FT-IR) and FT-Raman studies confirm the presence of various functional groups present in the grown crystal. The absorption spectrum of the titled crystal shows that the lower cut off wavelength lies at around 300 nm. The thermal analysis (TG/DTA and DSC) and Polarized light thermomicroscopy (PLTM) were carried out to find the thermal stability, melting point and phase transition of the title crystal. The second-order nonlinear optical (NLO) property of the grown crystal has been confirmed by Kurtz-Perry powder technique. First static hyperpolarizability and molecular orbital calculations were carried out using Gaussian 03W program based on B3LYP/3-21G basis set.

Full text of DOI:10.1016/j.saa.2012.07.048

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 798–805
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Growth and characterization of anilinium hydrogen sulfate (AHS) single crystals:
An organic nonlinear optical material
a
a
b
a,
⇑
N. Sudharsana , G. Subramanian , V. Krishnakumar , R. Nagalakshmi
a
Department of Physics, National Institute of Technology, Tiruchirappalli 620015, India
Department of Physics, Periyar University, Salem 636011, India
b
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
In the present work, anilinium hydrogen sulfate single crystals were grown and subjected to the struc-
tural, optical, thermal, vibrational, linear and nonlinear optical studies. The material exhibits second har-
monic generation and the calculated first-order hyperpolarizability, which is nearly 8 times that of urea.
"
"
"
The physico-chemical studies on
titled crystal have been reported for
the first time.
The material crystallizes in
noncentrosymmetry and thus it
exhibits SHG.
The calculated b is eight times that of
urea.
E
LUMO=0.104a.u
LUMO Plot
(
First Excited state)
g
E =0.472a.u
E
HOMO=-0.368a.u
HOMO Plot
HOMO (Ground state)
a r t i c l e i n f o
a b s t r a c t
þ
ꢁ
Article history:
Received 14 May 2012
Received in revised form 4 July 2012
Accepted 11 July 2012
Available online 20 July 2012
Single crystals of anilinium hydrogen sulfate (C H N ꢀ HSO , AHS) have been grown by slow evaporation
6
8
4
solution growth technique using water as a solvent. Powder X-ray diffraction (XRD) study has been car-
ried out to determine the lattice parameters. Fourier transform infrared (FT-IR) and FT-Raman studies
confirm the presence of various functional groups present in the grown crystal. The absorption spectrum
of the titled crystal shows that the lower cut off wavelength lies at around 300 nm. The thermal analysis
(
TG/DTA and DSC) and Polarized light thermomicroscopy (PLTM) were carried out to find the thermal sta-
Keywords:
Crystal growth
Computational techniques
Optical properties
Vibrational studies
Thermal properties
bility, melting point and phase transition of the title crystal. The second-order nonlinear optical (NLO)
property of the grown crystal has been confirmed by Kurtz-Perry powder technique. First static hyperpo-
larizability and molecular orbital calculations were carried out using Gaussian 03W program based on
B3LYP/3-21G basis set.
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
which have nonlinear optical properties larger than that of the
currently available inorganic materials. Organic materials may
Recently, there is a severe push in photonic material because of
their utility in constructing the devices for optoelectronic applica-
tions. The specific requirement is to develop organic derivatives
eventually replace inorganics in industrial applications, such as
electrooptic modulators and optical switches [1]. The asymmetric
þ
ꢁ
unit of the title compound, C
6
H
8
N
ꢀ HSO , contains two cations
4
and two anions which are linked to each other through N–H. . .O
hydrogen bonds, formed by all H atoms covalently bonded to the
N atoms. In addition, strong O–H. . .O anion–anion hydrogen-bond
⇑
Corresponding author. Tel.: +91 431 2503615; fax: +91 431 2500133.
E-mail address: nagaphys@yahoo.com (R. Nagalakshmi).
1
386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.07.048

N. Sudharsana et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 798–805
799
interactions are also observed. Bis(anilinium hydrogen sulfate) is
Experimental technique
one of the hybrid compounds, rich in H-bonds [2–4], which could
have potential importance in constructing sophisticated assem-
blies from discrete ionic or molecular building blocks due to the
strength and the directionality of hydrogen bonds [5].Amine salts
have attracted much attention as phase transition dielectric mate-
rials for their application in memory storage [6]. Recently, similar
structures containing anilinium cations have been reported.
Among examples, can be named the following ones: anilinium ni-
trate [7], anilinium picrate [8], anilinium hydrogenphosphite and
anilinium hydrogenoxalate hemihydrates [9].Aromatic amines
are very important in biology and chemical industry. Particularly,
aniline and its derivatives are used in the production of dyes, pes-
ticides and antioxidants [10].Raman and infrared vibrational spec-
tra throw light on the structural features, molecular conformation,
behavior of normal modes, effects of various types of intermolecu-
lar forces and nature of hydrogen bonding in optically important
substances [11]. Anilinium hydrogen sulfate (AHS) is one such re-
cently developed organic crystal and its growth and structure has
been reported [5]. To the best of our knowledge so far, no system-
atic study has been carried out on the vibrational, thermal, linear
and nonlinear optical properties of the title crystal. Hence our pres-
ent intention is to provide a complete study of this material with
respect to its physico-chemical properties.
Synthesis and crystal growth
The Anilinium Hydrogen Sulfate (AHS) was synthesized accord-
ing to the reaction scheme shown in Fig. 1(a).
Single crystals of AHS were grown by solution growth employ-
ing slow evaporation solution growth technique at room tempera-
ture of an aqueous solution of aniline and sulfuric acid in 1:1 ratio.
The solution was kept undisturbed. The colorless crystals were har-
vested after 2 weeks.
Solubility
The solubility of AHS has been determined for four tempera-
tures: 30, 60, 90 and 120 °C. The synthesized salt was used for sol-
ubility test. Solubility for AHS in water was determined by
dissolving the solute in water with continuous stirring. After
attaining saturation, the equilibrium concentration of the solute
was analyzed. This process was repeated for different tempera-
tures (30–120 °C). It is observed from the Fig. 1 (b).that AHS exhib-
its positive solubility temperature gradient in water and solubility
almost increases linearly with temperature as shown in Fig. 1(b)
[
16].
Computational details
Results and discussion
The computational approach allows the determination of
molecular NLO properties as an inexpensive way to design mole-
cule by analyzing their potential before synthesis and to determine
the higher order hyperpolarizability tensors of molecules [12]. The
quantum chemical computations were carried out on the anilinium
hydrogen sulfate based on density functional theory (DFT) using
Gaussian 03W program package [13], invoking gradient geometry
optimization. The geometry was taken from crystallographic Infor-
mation file and treated as an isolated molecule in the gas phase.
The geometries were optimized using the Becke’s three-parameter
hybrid functional combined with Lee–Yang–Parr exchange correla-
tion functional (B3LYP) method employing 3–21G basis sets. All
optimized structures were confirmed to be minimum energy
conformations. An optimization is complete when it has
converged-i.e., when it has reached a minimum on the potential
energy surface, thereby predicting the equilibrium structures of
the molecules. This criterion is very important in geometry optimi-
zation [14]. At the optimized structure, no imaginary frequency
modes were obtained proving that a true minimum potential sur-
face was found [15]. The b components of Gaussian 03W output
are reported in atomic units, the calculated values have to be con-
Powder X-ray diffraction analysis
The powder X-ray diffraction pattern shown in Fig. 3 has been
recorded using Panalytical xpert pro MPDO X-ray diffractometer
with Cu Ka (k = 1.5405 Å) radiation for the title crystal to identify
the structure and to estimate the lattice parameter values. The
peaks were indexed as shown in Fig. 2 using XRDA program and
lattice parameters have been confirmed. From the X-ray diffraction
ꢁ
33
verted into electrostatic units (1 a.u. = 8.3693 ꢂ 10
The density functional theory has been used to calculate the
dipole moment(
esu).
l
), mean polarizability h i, and the total first static
a
hyperpolarizability (btot) in terms of x, y, z components and are
given by following equations,
2
2
2
1=2
l
¼ ðlx
þ
ly
þ
lz
Þ
ð1Þ
ð2Þ
h
a
i ¼ 1=3ð
a
xx
þ
a
yy
þ
a
zz
Þ
2
x
2
y
2
z
1=2
btot ¼ ðb þ b þ b Þ
2
2
btot ¼ ½ðbxxx þ bxyy þ bxzzÞ þ ðb þ byzz þ byxx
Þ
yyy
2
1=2
þ ðbzzz þ bzxx þ bzyyÞ ꢃ
ð3Þ
Energy gap, total dipole moment, polarizability and the first hyper-
polarizability were calculated at the DFT (B3LYP).
Fig. 1. (a) Reaction scheme of anilinium hydrogen sulfate. (b) Solubility curve of
anilinium hydrogen sulfate.

8
00
N. Sudharsana et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 798–805
Fourier transform infrared (FTIR) and FT-Raman spectroscopic
analysis
The FTIR spectrum of AHS crystals was recorded in the range
ꢁ1
4
00–4000 cm
employing a Perkin-Elmer Spectrum one FTIR
spectrophotometer by the KBr pellet method to study the charge
transfer interactions in the title compound. Raman spectrum was
recorded using Nicolet DXR Smart Raman spectrometer. The vibra-
tional spectral analysis is performed on the basis of the character-
istic vibrations of the anilinium cation and hydrogen sulfate anion.
Their FTIR and Raman intensities corresponding to the different
vibrational are used to identify the functional groups unambigu-
ously. The measured FTIR and Raman band positions and their
assignments are given in Table 2. The frequency at which a partic-
ular group absorbs is dependent on its electron environment with-
in the molecule and its physical state. The formation of charge
transfer complex during the reaction of aniline with sulphuric acid
is strongly evidenced through the realization of important bands of
donor and acceptor in the FTIR and Raman spectrum (Fig. 4). The
þ
most prominent groups in AHS crystals are NH (cation) and
Fig. 2. Indexed powder X-ray diffraction spectrum of anilinium hydrogen sulfate
crystal.
3
ꢁ
HSO4 (anion). The Fig. 4.shows the FT-IR and FT-Raman spectra
of the title compound.
Table 1
Anilinium cation vibrations
Structural parameters of anilinium hydrogen sulfate crystal.
þ
The NH3 group has C
3
m
symmetry in the free State with a pyra-
(A ), (A ),
(E). All the four modes of vibrations are both Infrared
Identification codex
Present work
Reported work [2]
midal structure. Its normal modes of vibrations are
(E) and
m
1
m
1
2
1
þ
ꢁ
þ
ꢁ
m
3
m
4
Molecular formula
Crystal System
Space group
a (Å)
C H N ꢀ HSO
C H N ꢀ HSO
6
8
4
6
8
4
orthorhombic
orthorhombic
and Raman active [18]. The amino N of the anilinium cation forms
an N–H. . .O hydrogen bond with the O atom of hydrogen sulfate
anion. The hydrogen bond bridges two atoms that have high elec-
tronegativity (such as O and N) than hydrogen. The hydrogen
bonding forms the essential component of several NLO active com-
pounds which could be ascertained by vibration studies. The
hydrogen bond formation is clearly seen in FTIR spectrum than
Pca2
1
Pca2
1
14.0887
9.2402
12.8856
1677.48
8
14.3201
9.0891
12.8771
1676.04
8
b (Å)
c (Å)
3
v
(Å )
Z
in Raman spectrum [17]. So our discussion is mainly centered on
þ
most prominently contributing groups such as NH (ammonium
data, the material crystallizes in orthorhombic space group
Pca2 and the cell parameters are a = 14.0887 Å, b = 9.2402 Å,
3
ꢁ
cation) and HSO4 (bisulfate anion) of the Anilinium Hydrogen sul-
fate crystal. The spectrum carries a shoulder peak at 3391 cm for
NH asymmetric stretching vibration. Unfortunately mas NH vibra-
tion is absent in Raman spectrum. The broad band observed in high
shoulder band at
067 cm are assigned to symmetric NH3 stretching modes in
FT-IR. The corresponding medium intensity Raman band is ob-
served at 3069 cm . The observed NH3 stretching frequencies
are lowered from the expected range due to the intermolecular
N–H. . .O hydrogen bond interactions of AHS. The broadening of
1
ꢁ1
c = 12.8856 Å. The observed results are in good agreement with
the reported literature [5]. The prominent peaks satisfy the crystal-
line property of the title crystal. The lattice parameters were
shown in Table 1. The Fig. 3.illustrates the optimized structure of
AHS compound at DFT level. The asymmetric unit of anilinium
hydrogen sulfate contains two anilinium cation and a two hydro-
gen sulfate anion which are linked to each other through
N–H. . .O hydrogen bonds [5]. The AHS compound is internally
linked hydrogen bonded ion pair and hence regarded as a molecu-
lar crystal. The donor and acceptor molecules of sulfuric acid and
aniline complex are held together by the contacts of van der Waals
type [17].
þ
þ
3
3
ꢁ1
wavenumber region at 3049 cm
3
and
a
ꢁ1
þ
ꢁ1
þ
þ
the bands indicates the participation of the NH3 group in hydrogen
bonding [19]. The weak band in Raman spectrum identified at
ꢁ1
þ
1
609 cm
is assigned to the asymmetric deformation of NH3
vibration and the corresponding band is inactive in FTIR spectrum.
The symmetric deformation NH3 mode is observed at 1555 cm
þ
ꢁ1
as a weak band in FTIR and the corresponding band is absent in Ra-
man spectrum. The CN stretching vibration is observed as a weak
ꢁ1
band at 1214 cm in Raman spectrum. The rocking vibrations ap-
ꢁ1
pears at 1135 cm in FTIR as a weak band and the corresponding
ꢁ
1
Raman band appears at 1160 cm [20].
C–H vibrations
The Aromatic C–H stretching vibrations usually absorb as a
ꢁ1
weak to medium intense bands between 3120 and 3000 cm
[
2
(
21]. Weak combination and overtone bands appear in the region
ꢁ1
2 3 4 5 6
000–1650 cm . The ring C –H, C –H, C –H, C –H and C –H
ꢁ1
Fig. 3) stretching vibrations appears at 3049, 3061 cm in FTIR
ꢁ1
spectrum and it is observed in Raman at 3067 cm . The symmet-
ric NH3 stretching vibrations also fall in this region. The ring in-
plane bending bands appear in the 1300–1000 cm region [21].
þ
ꢁ1
Fig. 3. Optimized structure of anilinium hydrogen sulfate calculated at DFT level.

N. Sudharsana et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 798–805
801
Table 2
Observed FTIR and FT-Raman wavenumbers (in cmꢁ1) of anilinium hydrogen sulfate and its vibrational assignments.
FTIR wavenumber (cmꢁ1
)
Raman wavenumber (cm
ꢁ1
)
Band assignments
þ
3
3
2
–
1
1
1
–
–
1
1
–
–
–
7
6
4
–
391(sh)
049(br),3061(sh)
591–1745
–
masNH
3
þ
3067(ms)
–
1609(w)
msNH3
;
m
C ꢁ H
Overtone/combination
þ
dasNH ,Aromatic
m
m
C–C
C–C
3
þ
555(ms)
497(ms)
338(w),1327(w),1292(w)
–
–
–
d NH , Aromatic
s
3
Aromatic C–C stretching
C–H ip bending
C–N stretching, C–H ip bending
1226(w),1214(w)
1160(vw)
–
1027(w)
1003(s)
978(ms)
800(s)
ꢁ
ꢁ
þ
asymmetric stretching of SO in HSO4
;
q
NH ,C–H ip bending
3
3
þ
135(w)
091(ms),1024(w)
q
NH , C–H ip bending
Symmetric stretching of SO , C–C ip deformation, C–H ip bending
C–H ip bending, C–C ip deformation
–
C–H oop bending
C–H oop bending,C–C oop deformation
Ring deformation
C–C–C in-plane bending, NH3 torsion
3
ꢁ
3
35(s),687(s)
15(ms)
77(w)
–
618(w)
443(vw)
173(w)
þ
Lattice vibration mode
mas, asymmetric stretching;
s s
m , symmetric stretching; d ,symmetric bending; das asymmetric bending; ip, in-plane; oop, out-of-plane; q, rocking; v, very; s, strong; m, medium;
w, weak; sh, shoulder; br, broad.
ꢁ
1
from 1650–1450 cm . Accordingly, in the present work, the C–C
ꢁ1
stretching vibrations of AHS were identified at 1555(ms) cm
and 1497(ms) in FTIR. The corresponding Raman peak exhibits at
ꢁ
1
1
609(w) cm . An aromatic C@C ring vibration or ring ‘‘breathing
ꢁ1
ꢁ1
band’’ at ꢄ1600 cm . Generally the band at 1000–1100 cm
arises from in-plane deformations. The bands at 1091(ms),
024(w) in FTIR and 1027(w), 1003(s) in Raman was assigned to
aromatic C–C in-plane deformations. The band at 735 cm in FTIR
arises from out-of-plane bending. The C–C–C out-of-plane defor-
1
ꢁ1
ꢁ1
mation occurs at 477(w) cm in FTIR and the corresponding Ra-
man spectrum at 443(vw) cm
ꢁ
1
. These results are exactly
consistent with reported value [23].
Hydrogen sulfate anion vibrations
Sulfuric acid has two hydroxyl groups and two double-bonded
oxygen atoms on the central sulfur atom. The loss of the first pro-
ton results in a negative charge shared by the three oxygens. The
ꢁ
HO ꢁ SO ion resembles the sulfonic acid salts in that it has bands
3
ꢁ
1
ꢁ
at 1190–1160 cm
for asymmetric SO stretch and 1080–
3
ꢁ
1
ꢁ
1
015 cm
for symmetric SO3 stretch [21]. The intermolecular
charge transfer from the donor to acceptor group can induce large
deviation of both the molecular dipole moment and the molecular
Fig. 4. FT-IR and FT-Raman spectrum of anilinium hydrogen sulfate crystal.
polarizability, producing FTIR and Raman activity strong. The spec-
ꢁ
trum of the HSO4 ion, which possesses C
3m
symmetry, shows three
In the present work, the aromatic C–H in plane bending shows
ꢁ1
bands, the totally symmetric S–(OH) stretch at 885 cm , the to-
ꢁ
1
weak band in the region 1292–1024 cm in FTIR and the counter-
part of the Raman spectrum shows the vibrational frequency in the
3 3
tally symmetric SO stretch and asymmetric SO stretch [24]. The
ꢁ1
ꢁ1
weak peak at 1024 cm in FTIR and 1027 cm in Raman are as-
ꢁ
1
region 1226–1003 cm . Usually the most prominent and most
informative bands of aromatic compounds occurs in the low-fre-
ꢁ
signed to symmetric stretching mode of SO vibrations. The very
3
ꢁ1
weak band in Raman appears at 1160 cm is attributed to asym-
ꢁ1
quency range between 900 and 675 cm . These strong absorption
bands in this region result from the out-of-plane (‘‘oop’’) bending
of the ring C-H bonds. The strong band observed at 735, 687 and
ꢁ
metric stretching of SO3 anion whereas it is inactive in FTIR. The
formation of the charge transfer complex through the reaction of
aniline with sulfuric acid is strongly evidenced by the presence
of the above main characteristic infrared bands of the donor and
acceptor in the spectrum of the product. The occurrence of inter-
molecular charge transfer is confirmed in vibrational spectral
study.
ꢁ1
8
00 cm in FTIR and Raman spectrum, respectively is attributed
to ring C–H out-of-plane bending. The in-plane ring deformation
[21,22]. The weak band at
15 cm in FTIR and the corresponding band at 618 cm in Ra-
ꢁ1
is expected to occur at 615 cm
6
ꢁ1
ꢁ1
man spectrum is assigned to ring in-plane deformation vibration.
UV–Visible spectrum
C–C vibrations
There are six equivalent C–C bonds in benzene and conse-
quently there will be six C–C stretching vibrations. The aromatic
C–C vibration known as semicircle stretching gives rise to the char-
acteristic bands in the FT-IR spectra, covering the spectral range
Optical absorption measurements were carried out using the
Perkin Elmer Lambda 35 spectrophotometer in the 190–1100 nm
region. The absorption edge is observed at around 300 nm from
the Fig. 5a. The absence of absorption in the region between 300

8
02
N. Sudharsana et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 798–805
between hm and (ahm
)2 by extrapolating the linear portion of the
curve to zero absorption as shown in the Fig. 5b. The direct optical
band gap 4.9 eV is found to be the major transition taking place in
the material.
and 1100 nm is an advantage, as it is the key requirement for mate-
rials having NLO properties. As a result, it can be used as a potential
material for SHG in the visible region down to blue and violet light,
which makes it suitable for laser frequency doubling and related
optoelectronic application.
The dependence of optical absorption coefficient with the pho-
ton energy helps to study the band structure and the type of tran-
sition of electrons [25]. The transmittance (T) was used to calculate
Thermal studies
TG/DTA and DSC analysis
the absorption coefficient (
where t is the thickness of the sample in mm.
According to the Tauc relation [26] the absorption co-efficient
a
) using the formula
a
= 1/t ꢂ ln(1/T)
The TG/DTA and DSC analysis gives information regarding phase
transition, melting point, composition, water of crystallization and
different stages of decomposition of the crystal system. The TG/
DTA and DSC studies were carried out in the nitrogen atmosphere
at a heating rate of 10 °C min from 30 to 1000 °C using thermal
analyzer (TG/DTA6200) and Netzsch DSC 204, respectively. The
TGA/DTA and DSC curves are presented in Fig. 6 (a) and (b),
respectively.
a, for a material is given by the absorption coefficient
a
of a crys-
ꢁ1
talline solid obeys the following relation
n
ð
ahm
Þ ¼ Aðh
m
ꢁ E
g
Þ
ð4Þ
where E
g
is the energy gap corresponding to a particular transition
occurring in the crystal, A is the band edge constant, is the transi-
The TG thermogram shows two stage decompositions. The
first stage of AHS undergoes mass loss (40%) from 154 to
m
tion frequency, and the exponent n characterizes the optical absorp-
tion process. The values of n can be 1/2, 3/2, 2, and 3 depending on
the transitions such as direct allowed, direct forbidden, indirect
allowed, and indirect forbidden transition, respectively [27]. The
band gap energy value was determined from the graph drawn
2
66 °C due to the evolution of water of crystallization in the crys-
tal. The mass loss (40%) in the second stage from 356 to 397 °C
for AHS agrees with the expected mass loss for sulfonation. The
plateau region in the TG thermogram (Fig. 6(a)) for AHS in the
temperature region 267–356 °C is showing the stability of the
corresponding amino benzene sulfonic acid (due to sulphona-
tion). Finally, the decomposition of corresponding amino benzene
sulfonic acid (ABSA) of AHS crystal occurs by deamination, des-
ulfonation followed by ring rupture [28,29]. From the TGA, It is
observed that the compound is stable up to 153 °C. The DTA
shows three endothermic peaks. The DTA curve shows a first
weak endothermic peak occurring at 214 °C. This peak is ascribed
to a phase transition. The AHS is congruently melting compound
as it decompose during melting point. The second weak endo-
thermic peak occurs at 246 °C which corresponds to the melting
of the sample which is identical to the sharp endothermic peak
observed in DSC trace. Melting point experimentally determined
using melting point apparatus (245 °C) is also same as taken from
DSC (Fig. 6(b)). This is followed by another endothermic peak at
3
90 °C coincides with the weight loss due to major decomposi-
tion of the sample in the TGA curve. Thus the thermal stability
of AHS crystal is found to be up to 153 °C to be used for optical
applications.
Polarized light thermomicroscopy (PLTM)
Linkam DSC600 hot stage, with a Leica DMRB microscope, Sony
CCD-IRIS/RGB video camera, Real Time Video Measurement System
software by Linkam for image analysis. Images obtained by the
combined use of polarized light and wave compensators, 200ꢂ
magnifications, scanning rate 10 °C/min. This technique is a valu-
able tool to study phase transformations. Moreover, low energy
phase transitions, for instance some solid–solid phase transitions,
that may not detected in DSC experiments, can be visualized in
PLTM experiments, as different phases give often rise to different
visual patterns [30].
PLTM experiments were carried out between 25 and 200 °C in
shown in Fig. 6c. In the temperature range studied we just see
the very beginning of the fusion process (clearly evident at about
1
95 °C, due to the sample contour softening).From TG/DTA curves
(Fig. 6a), fusion with decomposition starts at about 200 °C and the
first decomposition step is concluded at about 275 °C. In PLTM the
experiment was finished at 200 °C and therefore we just see the
very onset of the fusion process (195 °C).
Non linear optical studies
)2 vs. h
Fig. 5. (a) UV–Vis spectrum of anilinium hydrogen sulfate crystal. (b) (ahm m
of anilinium hydrogen sulfate crystal.
The SHG efficiency for the title crystal measured by Kurtz’s
powder technique generates the second harmonic output by

N. Sudharsana et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 798–805
803
Fig. 6. (a) TG/DTA spectrum of anilinium hydrogen sulfate crystal. (b) DSC spectrum of anilinium hydrogen sulfate crystal. (c) Photomicrographs obtained in the first heating
run.
irradiating the powder samples of randomly oriented crystallites.
Table 3
The powdered sample sandwiched between two glass slides is
subjected to the output of a Q-Switched Nd:YAG laser emitting a
fundamental wavelength of 1064 nm. The SHG efficiency was con-
firmed by the emission of green radiation (532 nm). The input and
output SHG energy is shown in Table 3. The SHG efficiency was
compared with urea and it was found to be 0.4 times greater than
that of urea crystal.
The input and output energy during SHG measurement.
Laser Wavelength (nm)
1064
Input power (J)
Output (mJ)
Urea
AHS
3.67
0.68
8.9
is the principal dipole moment axis and it is parallel to the charge
transfer axis) direction, the biggest values of hyperpolarizability
are noticed and subsequently delocalization of electron cloud is
more in that direction. This is due to the intermolecular hydrogen
bonding. The connection between the electric dipole moments of
an organic molecule having donor–acceptor substituent and first
hyperpolarizability is widely recognized in the literature [32].
First-order hyperpolarizability(b) and molecular orbital calculations
The first-order hyperpolarisability(bijk) of the AHS is calculated
using B3LYP/3-21G basis set using Gaussian 03W package. The the-
oretical calculation seems to be more helpful in the determination
of particular components of b tensor than in establishing the real
values of b. Before calculating hyperpolarizability the molecular
geometry is optimized. The calculated values of hyperpolarizability
is given below in the Table 4. From the Table 4, it was suggested
that the title compound is polar having non-zero dipole moment
and hyperpolarizability. Dipole moment and hyperpolarizabil-
ity(btotal) is calculated using the Eqs. 1 and 3, respectively. The btotal
The maximum b was owing to the behavior of non-zero
l value.
The electric dipoles may enhance, oppose or at least bring the di-
poles out of the required net alignment necessary for NLO proper-
ties such as btotal values [31]. The presence of intermolecular
charge transfer is confirmed with the vibrational spectral study.
The theoretically calculated first order hyperpolarizability (btotal
)
ꢁ
30
ꢁ30
was calculated to be 2.261878 ꢂ 10
esu. Domination of particu-
and dipole moment of AHS are 2.261878 ꢂ 10
esu and 9.20De-
lar components indicates that the substantial delocalization of
bye, respectively. The calculated value of b is 8 times that of urea.
ꢁ30
charges is more in those directions. It is noticed that in bxxx (which
The b value for urea is 0.2823 ꢂ 10
esu. Molecules exhibiting

8
04
N. Sudharsana et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 798–805
ꢁ
Table 4
C-H of anilinium cation and S–OH of HSO4 anion. The HOMO ? -
LUMO transition and the small HOMO–LUMO energy gap explain
the probable intermolecular charge transfer (ICT) takes place from
aniline electron-donor group to the sulfuric acid electron acceptor
group to form anilinium hydrogen sulfate charge transfer complex
The first-order hyperpolarizability(b) of Ani-
linium Hydrogen Sulfate derived from DFT
calculations.
b
b
b
b
b
b
b
b
b
b
b
xxx
xxy
xyy
yyy
zxx
xyz
zyy
xzz
yzz
zzz
tot
ꢁ218.4228464
ꢁ0.8042979
ꢁ47.79498
ꢁ33.1542454
7.623626
3.9340774
6.1846547
5.7455819
ꢁ14.0040391
39.9852141
2.261878
[
34].
Conclusions
The AHS single crystals have been grown by slow evaporation
method. From the powder X-ray diffraction pattern, the unit cell
parameters are calculated and the orthorhombic structure is con-
firmed. The optical absorption study reveals a cut-off wavelength
around 300 nm and the band gap of 4.9 eV. The presence of all
the fundamental functional groups of the grown crystal is con-
firmed by FTIR and FT-Raman analysis. From TG/DTA, AHS is
thermally stable up to 153 °C. The NLO property is confirmed
using Nd:YAG laser of wavelength 1064 nm and the Second
harmonic generation efficiency is estimated to be 0.4 times that
l
x
l
y
l
z
l
ꢁ7.3569
ꢁ4.0663
3.7501
9.2045
Dipole moment (
ability b (ꢁ2
l
x
) in Debye, hyperpolariz-
ꢁ
30
x
;
x,
) in 10
e.s.u.
of urea. The calculated first-order hyperpolarizability value is
large hyperpolarizabilities have a strong NLO potential and could
be used, for optoelectronics and fabricating range of optical
devices.
ꢁ30
2
.261878 ꢂ 10
esu, which is nearly eight times that of urea.
The lowering of HOMO and LUMO energy gap clearly reveals the
charge transfer interactions taking place within the molecule. This
clearly indicates that in acid–base hybrid crystals, hydrogen bond
plays an important role not only in the creation of crystal structure
and its stability, but also in the enhancement of the hyperpolariz-
ability b of the crystal.
The frontier orbital’s (HOMO and LUMO) find out the way in
which the molecule interacts with other species. The frontier orbi-
tal gap facilitates to characterize the chemical reactivity and
kinetic stability of the molecule. A molecule with a small frontier
orbital gap is more polarizable and is usually related with a high
chemical reactivity, low kinetic stability and is also termed as soft
molecule. Highest occupied molecular orbital (HOMO) is directly
related to the ionization potential, while energy of the lowest
unoccupied molecular orbital (LUMO) is directly related to the
electron affinity. In the Fig. 7 the red color indicates the positive
phase and the green color indicates the negative phase. The HOMO
is the orbital that primarily acts as an electron donor and the LUMO
is the orbital that mainly acts as the electron acceptor. The 3D plots
of the frontier orbitals HOMO and LUMO of AHS is shown in Fig. 7.
The HOMO–LUMO gap value of the AHS compound is 0.472a.u. It is
seen from the HOMO and LUMO energy gap that there is an inverse
relationship between the hyperolarizability and the HOMO–LUMO
energy gap [33]. It can be seen from the Fig. 7. that, the HOMO is
Acknowledgements
The author R.N is thankful to Council of Scientific and Industrial
Research, New Delhi for the financial assistance under major re-
search project (03/1158/10/EMR II) and N.S is thankful to CSIR
for awarding JRF in this project. The authors are thankful to
Dr.Archna Sharma, Prof.Rui Fausto, Prof. M.E.S. Eusébio, Depart-
ment of Chemistry, University of Coimbra, Portugal for extending
the facility for FT-Raman and polarized light thermomicroscopy
study under Indo-Portuguese (DST-FCT) joint research project.
The authors are also thankful to SAIF, IIT Madras for the FTIR and
DSC measurements.
þ
delocalized more on amino group NH3 and on ring C–C of anilini-
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