Spectral, thermal and optical properties of adenosinium picrate: A nonlinear optical single crystal

Article abstract of DOI:10.1016/j.saa.2011.12.029

A new organic nonlinear optical material adenosinium picrate (C ₁₀H₁₄N₅O₄⁺, C₆ H₂ N₃ O₇^-) was synthesized. The single crystal X-ray diffraction revealed the non-centrosymmetric crystal structure, which is an essential criterion for second harmonic generation. The crystalline nature of the grown crystals was confirmed using powder XRD techniques. Molecular structure was confirmed by NMR spectral analysis and functional groups were identified by FT-IR spectral analysis. The optical transmittance window and the lower cutoff wavelength of the AP have been identified by UV-vis-NIR studies. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder test with Nd:YAG laser radiation shows second harmonic generation.

Full text of DOI:10.1016/j.saa.2011.12.029

Spectrochimica Acta Part A 89 (2012) 119–122
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectral, thermal and optical properties of adenosinium picrate: A nonlinear
optical single crystal
S. Gowria, T. Uma Devib,∗, D. Sajanc, S.R. Bheeterd, N. Lawrencee
a Department of Physics, Cauvery College for Women, Tiruchirappalli 620018, India
b Department of Physics, Government Arts College for Women (Autonomous), Pudukottai, India
c Department of Physics, Bishop Moore College, Mavelikara, Alappuzha 690 110, Kerala, India
d Department of Chemistry, St. Joseph’s College (Autonomous), Tiruchirappalli 620018, India
e Department of Physics, St. Joseph’s College (Autonomous), Tiruchirappalli 620018, India
a r t i c l e i n f o
a b s t r a c t
A new organic nonlinear optical material adenosinium picrate (C10H14N5O4+, C6 H2 N3 O7−) was synthe-
sized. The single crystal X-ray diffraction revealed the non-centrosymmetric crystal structure, which is
an essential criterion for second harmonic generation. The crystalline nature of the grown crystals was
confirmed using powder XRD techniques. Molecular structure was confirmed by NMR spectral analysis
and functional groups were identified by FT-IR spectral analysis. The optical transmittance window and
the lower cutoff wavelength of the AP have been identified by UV–vis–NIR studies. Thermo gravimetric
analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder
test with Nd:YAG laser radiation shows second harmonic generation.
Article history:
Received 7 October 2011
Received in revised form 3 December 2011
Accepted 15 December 2011
Keywords:
Crystal growth
X-ray diffraction
Optical material
Thermal studies
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
organic acid because of the presence of three electron withdrawing
nitro groups which makes it as a good ␲-acceptor for neutral carrier
Recent advances in organic nonlinear optical (NLO) materials
have invoked a large revival of interest in this area of research
on account of their widespread industrial potential applications
[1–3]. Organic molecules have much greater design flexibility than
inorganic compounds, which allows for the fine-tuning of NLO
responses, and they can be much cheaper and easier to fabri-
cate. The NLO effects in organic molecules are usually electronic in
nature, which leads to fast nonlinear response. The architectural
flexibility allows for precise molecular design and the determi-
nation of structure–property relationships. Low-lying electronic
transitions in the UV–visible region improve the NLO efficiencies
of organic systems [4]. Many of these molecular organic crystals
owe their nonlinear optical properties to the presence of delocal-
ized ␲-electron systems linking donor and acceptor groups which
enhance the necessary asymmetric polarizability [5].
donor molecule. The picrate has increased molecular hyperpolariz-
ability because of the proton transfer and remarkable second-order
NLO activity (ꢀ2) [10]. Picric acid is having a tendency to form the
stable picrate compounds with various organic molecules such
as l-tryptophan [11], l-proline [12], and glycine [13], due to the
presence of active ␲- and ionic bonds [14]. The title compound
adenosinium picrate (AP) crystallizes in non-centrosymmetric
space group P212121 and the structure exhibit interesting patterns
of N H· · ·O hydrogen bonding. Adenosine acts as the donor and
picric acid as electron acceptor which provides the ground state
charge asymmetry of the molecule required for second-order
nonlinearity (Fig. 1). The crystal structure of the title compound
has already been reported [15]. The present study includes the
growth of AP by slow evaporation method. The grown crystal has
been subjected to X-ray diffraction study, FT-IR, UV–vis spectral
analysis and thermal analysis. The NLO properties of the title
compound were confirmed by the Kurtz–Perry technique.
Adenosine (6-amino-9␤-d-ribofuranosyl-9H-purine) is an
essential biological nucleoside. Adenosine derivatives have been
the subject of investigations owing to biological significance [6,7].
Adenosine interacts with carboxylic acids, resulting in protonation
of the purine ring, giving salts with enhanced crystallinity due to
hydrogenbonding interactions [8,9]. Picric acid is an interesting
2. Material synthesis and crystal growth
Commercially available adenosine and picric acid were taken
in stoichiometric ratio were dissolved in double distilled water and
stirred well using a temperature controlled magnetic stirrer to yield
a homogeneous mixture of solution. Then the solution was allowed
to evaporate at room temperature, which yielded yellow crystalline
∗
Corresponding author. Tel.: +91 0431 4050500; fax: +91 0431 2751234.
E-mail address: kavin shri@yahoo.co.in (T. Uma Devi).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.12.029

120
S. Gowri et al. / Spectrochimica Acta Part A 89 (2012) 119–122
Fig. 1. Chemical structure of AP.
salt of AP. The process of recrystallization was carried out to purify
the synthesized salt. As the water solvent yielded very small crys-
tals attempts were made to grow AP crystals from mixed solvents.
From several trials it was observed that the mixture of equal vol-
ume of acetone and water yielded relatively transparent crystals of
AP (Fig. 2).
3. Discussion
3.1. X-ray diffraction studies
Fig. 3. Powder X-ray diffraction AP.
The single crystal X-ray diffraction analysis of AP was carried
out using ENRAF NONIUS CAD4 single crystal X-ray diffrac-
tometer equipped with MoK␣ (ꢁ = 0.71071 A) radiation. The
and 3310–3280 cm−1, respectively [17,18]. In adenosinium picrate
the O H stretch and asymmetric NH2 stretching vibration fall in
the same region. The broad band in IR spectrum at 3430 cm−1
corresponds to the asymmetric NH2 stretch. The internal defor-
mation vibrations known as NH2 scissoring wavenumber is found
in the region 1615–1650 cm−1 [17–19]. The intense IR bands at
1631 cm−1 can be attributed to scissoring mode of the NH2 group.
The in-plane bending O H deformation vibration usually appears
as a strong band in the region 1400–1260 cm−1 in the IR spec-
trum, which gets shifted to higher wavenumbers in the presence of
hydrogen bonding. The O H in-plane bending vibration is observed
in IR at 1367 cm−1. The C N stretching vibrations are observed in
the region 1250–1340 cm−1 in all the primary aromatic amines.
˚
compound crystallizes in orthorhombic form with lattice param-
´
˚
´
˚
´
3
˚
˚
eters a = 8.776 A, b = 33.013 A, c = 6.728 A and V = 1949 A . These
values agreed well with the reported values [15]. The recorded
powder X-ray diffraction pattern of AP sample is shown in Fig. 3.
The sharp and well-defined Bragg peaks at specific 2ꢂ angles testi-
monies the crystallinity of the material.
3.2. Vibrational studies
The vibrational analysis of adenosinium picrate was performed
on the basis of the characteristic vibrations of amino group, car-
bonyl group, nitro group vibrations and phenyl ring modes. The
observed FT-IR spectra are presented in Fig. 4.
The hydroxyl stretching and bending can be identified by their
broadness and strength of the band which is dependent on the
extended of hydrogen bonding. The non-hydrogen bonded or free
hydroxyl group absorbs strongly in the 3600–3500 cm−1 region
while the existence of intermolecular hydrogen bond formation
can lower the O H stretching wavenumber to the 3500–3200 cm−1
region with the increase in IR intensity and broadness [16]. In sat-
urated amines, the asymmetric NH2 stretch and their symmetric
counterpart are usually expected in the region 3380–3350 cm−1
The observed strong band at 1273 cm−1 in IR is ascribed to C
N
stretching. The rocking mode of the NH2 group appears in the range
1000–1100 cm−1 with variable IR intensity [20]. The observed weak
band at 1048 cm−1 in IR spectrum is attributed to the appreciable
contribution from the CNH angle bending suggesting its origin due
to the rocking mode. It is a strongly mixed mode containing contri-
bution from the ring stretching and the rocking modes. The wagging
mode of the NH2 group appears in the range 500–700 cm−1. The
Fig. 2. Photograph of the as-grown single crystal of AP.
Fig. 4. FT-IR spectrum of AP.

S. Gowri et al. / Spectrochimica Acta Part A 89 (2012) 119–122
121
Fig. 6. 1H NMR spectrum of AP.
of substantial absorption in the entire visible region might enable
achievement of microscopic NLO response with non-zero values.
Fig. 5. UV–vis–NIR spectrum of AP.
3.4. NMR spectral studies
observed weak band at 613 cm−1 in IR spectrum corresponds to
the NH2 wagging mode. The O H out of plane bending vibration
gives rise to a broad band in the region 700–600 cm−1. The position
of this band is dependant on the strength of the hydrogen bond.
The broad band at 707 cm−1 in the infrared spectrum is attributed
to the O H out of plane bending mode.
The proton 1H NMR spectrum of AP was recorded using JEOL
GSX 400 model at 27 ◦C. The chemical shift values of the protons
are plotted on the X-axis and the intensity is plotted on the Y-axis
(Fig. 6). The appearance of ten proton signals in the spectrum con-
firms explicitly its molecular structure. The signals appearing in the
aliphatic region of the spectrum are due to different methine pro-
tons of furanose ring of the sugar moiety. The methylene proton of
CH2 OH group is downfield shifted to ı 8.5 ppm due to electroneg-
ative oxygen of the OH group. The singlet observed at ı 8.754 ppm
has been assigned to C3 and C5 aromatic protons of the kind in the
picrate moiety. The same was observed at ı 11.94 ppm in free picric
acid. This upfield shift of frequency is attributed to an increase in
electron density as a result of charge transfer in the complex. The
absence of singlet peak around ı 11.94 ppm which was assigned to
the O H proton of the free picric acid suggests that the picric acid
is ionized and is present as a picrate ion [22,23].
The mode C C is assigned as a medium band at 1489 cm−1
in IR spectrum [21]. The asymmetric and symmetric stretching
vibrations of NO2 generally give rise to bands in the regions
1500–1570 cm−1 and 1300–1370 cm−1 in nitrobenzene and sub-
stituted nitrobenzene [16–20] respectively. In adenosinium picrate
medium IR bands at 1561 and 1335 cm−1 attributed to NO2 asym-
metric and NO2 symmetric stretching vibrations, respectively. The
lowering in both these stretching modes, is attributed to the
intermolecular hydrogen bonding and conjugation of NO2 with
the aromatic ring. The nitro group deformation vibrations, which
include NO2 scissoring, NO2 wagging and NO2 rocking, usually
occur at wavenumbers lower than 950 cm−1. For the majority
of compounds, the scissoring mode possesses the higher vibra-
tional wavenumbers of the three deformations, and it is by far
the most characteristic deformation mode. The NO2 rocking mode,
on the other hand, has the lowest wavenumber for these three
deformations [21]. The NO2 scissoring vibrations in aromatic nitro
compounds are expected around 825 cm−1. The broad band at
907 cm−1 in IR spectrum corresponds to the NO2 scissoring mode.
The enhancement of NO2 scissoring modes is attributed to the
conjugation of NO2 with the aromatic ring [16–20]. The wagging
vibrations of NO2 group normally appear around 760 cm−1,while
the rocking mode located at 500 cm−1. The bands corresponding
to wagging and rocking vibrations of NO2 appears at 786 cm−1 and
535 cm−1 in IR respectively, which is supported by results reported
in literatures [17–21].
3.5. Thermogravimetric analysis
Analysis of AP was carried out using a NETZSCH thermal analy-
sis system between 30 and 900 ◦C. The TGA and the corresponding
DTA traces are shown in Fig. 7. The TGA trace illustrates absence
3.3. Optical transmittance studies
Optical transmittance is an important parameter for an NLO
crystal. The optical transmittance of AP dissolved in distilled water
recorded using Shimadzu model 1601 in the range 190–1100 nm
is shown in Fig. 5. The spectrum reveals strong absorption bands
attributed to the charge-transfer transition in addition to the usual
␲ → ␲* bands of picrate ion in the complex and appears at 356 nm
and has low absorption in the entire visible region. The absence
Fig. 7. TGA/DTA spectrum of AP.

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S. Gowri et al. / Spectrochimica Acta Part A 89 (2012) 119–122
of any weight loss up to 182 ◦C but a major weight loss occurring
in three stages between 249, 290 and 462 ◦C. The total weight loss
corresponds to 46.1% above 462 ◦C, and the resulting residue under-
goes degradation up to 800 ◦C. No phase transition is observed in
this region which enhances the temperature range of the crystal
for NLO applications. The thermal resistance offered by the title
crystal has been observed up to 182 ◦C. Hence the present mate-
rial may be a promising candidate for all types of nonlinear optical
applications.
Acknowledgments
The authors are grateful to Dr. A. Chandramohan, Department
of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts
and Science, Coimbatore for fruitful discussions. The authors thank
Laser Research Lab, B.S. Abdur Rahman University, Chennai for
extending the facilities to measure SHG efficiency.
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a
molecular nonlinearity. The study of nonlinear optical conversion
efficiency has been carried out using the modified experimen-
tal setup of Kurtz and Perry [18]. A Q-switched Nd: YAG laser
beam of wavelength 1064 nm, pulse width of 8 ns and with a rep-
etition rate of 10 Hz was used. The grown single crystal of AP
was powdered with a uniform particle size and then packed in a
microcapillary of uniform bore and exposed to laser radiations.
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4. Conclusion
Single crystals of adenosinium picrate were grown from solu-
tion method. The unitcell parameters were confirmed by single
crystal X-ray diffraction analysis. The sharp well-defined peaks
confirm the crystalline nature of the materials. It is found that
the crystal belongs to the orthorhombic crystal system and
space group P212121. Molecular structure was confirmed by
NMR spectral analysis and functional groups were identified by
FT-IR spectral analysis. Thermal analyses indicated that the crys-
tal has good thermal stability. The optical property has been
assessed by UV–vis measurement showed the absence of absorp-
tion in the entire visible region. Powder test with Nd:YAG laser
radiation shows second harmonic generation. Hence it could
be suggested that this material is better befitted for optical
applications.
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