Synthesis, growth, structural and optical studies of organic nonlinear optical material - Piperazine-1,4-diium bis 2,4,6-trinitrophenolate

Article abstract of DOI:10.1016/j.saa.2014.04.095

Piperazine-1,4-diium bis 2,4,6-trinitrophenolate is one of the useful organic materials with nonlinear optical (NLO) and pharmaceutical applications. The material was grown by slow evaporation solution growth method at room temperature. The crystal system

Full text of DOI:10.1016/j.saa.2014.04.095

Accepted Manuscript
Synthesis, Growth, structural and optical studies of organic nonlinear optical
material- Piperazine-1,4-diium bis 2,4,6-trinitrophenolate
S. Suguna, D. Anbuselvi, D. Jayaraman, K.S. Nagaraja, B. Jeyaraj
PII:
S1386-1425(14)00668-4
http://dx.doi.org/10.1016/j.saa.2014.04.095
SAA 12059
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
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Revised Date:
Accepted Date:
15 January 2014
23 March 2014
13 April 2014
Please cite this article as: S. Suguna, D. Anbuselvi, D. Jayaraman, K.S. Nagaraja, B. Jeyaraj, Synthesis, Growth,
structural and optical studies of organic nonlinear optical material- Piperazine-1,4-diium bis 2,4,6-trinitrophenolate,
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.
2014.04.095
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Synthesis, Growth, structural and optical studies of organic nonlinear
optical material- Piperazine-1,4-diium bis 2,4,6-trinitrophenolate.
S.Suguna a, D.Anbuselvi b, D.Jayaramanc, K.S.Nagaraja a ,B.Jeyaraj a*
a Department of Chemistry, Loyola Institute of Frontier Energy (LIFE),
bDepartment of Physics, Loyola College, Chennai-34
cDepartment of Physics, Presidency College,Chennai-34.
Abstract
Piperazine-1,4-diium bis 2,4,6-trinitrophenolate is one of the useful organic materials with
nonlinear optical (NLO) and pharmaceutical applications. The material was grown by slow
evaporation solution growth method at room temperature. The crystal system and lattice
parameters were identified by single crystal XRD analysis. The grown material crystallizes in
monoclinic system with P21/n space group. The main functional groups NH2,NO2,C-N,C=C, and
phenolic 'O' atom were identified using FTIR analysis. The protons and carbons of grown crystal
1
13
with various chemical environments were studied by H and C NMR spectroscopy to confirm
the molecular structure. The optical properties of the crystal were studied by UV-vis-NIR
spectroscopy and the transmission 100% range starts from 532nm onwards. The optical band gap
was measured as 2.63eV from the plot of (αhν)2 vs hν . The thermal stability was detected at
304.1oC using TG-DTA analysis. The dielectric studies of the sample were carried out at different
temperatures in the frequency range from 50Hz to 5MHz to establish the dielectric nature of the
crystal. Photoconductivity measurements were carried out on the grown crystal. The Second
Harmonic Generation (SHG) of the crystal was tested to confirm the nonlinear optical property.
Keywords: Crystal structure, X-ray diffraction, Growth from solution, Single crystal growth,
Organic compounds, Dielectric materials.
* Corresponding author:
Dr. B.Jeyaraj
Loyola College, Chennai-34.
Ph: +91– 44–28178200, Ext.301
E-mail: jayaraj.boniface@gmail.com

1. Introduction
Second order non-linear optical (NLO) crystals are widely used to convert the frequency of
coherent laser sources. Laser based imaging communications like remote sensing, optical data
storage and optical computing, optoelectronics and counter measure systems require improved
NLO materials to accomplish such conversion [1,2]. Organic crystals nowadays have been
attracting much attention due to their superiority over the conventional inorganic substances for
many applications. The advantages of organic materials over their inorganic counterparts are that
they have high electronic susceptibility (χ), hyperpolarisability (β), facile modification through
standard synthetic methods and relative ease of device processing [3]. Organic complexes were
used in different pharmaceutical applications [4, 5] micro-emulsion and also organic
semiconductors [6, 7].
Piperazine is the most important building block of recent drug discoveries [8].Picric acid
derivatives are used in human therapy such as treatment of burns, antiseptic and astringent agent
[9].Besides pharmaceutical applications, several complexes of picric acid with organic basic
molecules exhibit nonlinear applications[10]. Donor-Acceptor groups in benzene derivatives
produce high molecular nonlinearity. Picric acid has been studied for its ability to form salts
which involve electrostatic forces, multiple hydrogen bonds of different strengths and π- π
stacking interactions. Picric acid forms crystalline picrates with various organic compounds
through ionic, hydrogen bonding and π- π interactions [11, 12]. It is known that picric acid acts
not only as an electron acceptor to form various π stacking complexes with other aromatic
molecules but also as an acidic ligand to form salts through specific electrostatic or hydrogen bond
interactions[13,14]. Many new organic crystals have been examined based on the predictive
molecular engineering approach and have been shown to have potential applications in
telecommunications and optical information processes [15]. Other advantages of organic
compounds involve amenability for synthesis, multifunctional substitution, higher resistance to
optical damage and maneuverability for device applications [16]. Molecular flexibility of organic

materials is an added advantage to enhance the nonlinear optical properties in a desired manner
[17]. In addition, they have large structural diversity. By adopting molecular engineering methods
in chemical synthesis one can easily refine the optical properties of organic molecules [18].
There is an increasing demand for single crystals to find applications in the development of
technology and devices for their NLO property. Therefore, in the present investigation, the
compound piperazine-1,4-diium bis 2,4,6-trinitrophenolate was grown first as a single crystal
using slow evaporation technique. The growth of the crystal was followed by detailed
characterization studies such as single crystal XRD study, UV-vis-NIR, FTIR and NMR spectral
studies, thermal, dielectric, photoconductivity and SHG measurements to analyze structural
property, transmission range, various functional modes, molecular structure, thermal stability,
dielectric behavior, and photoconductivity and NLO property of the grown material.
2. Experimental Procedure
2.1. Material synthesis
Single crystals of Piperazine-1,4-diium bis 2,4,6-trinitrophenolate were grown by slow
evaporation solution growth method at room temperature. Piperazine and Picric acid with 4:1
molar ratio were dissolved in deionized water to get a clear solution and the solution was stirred
well for homogeneity. Initially the pH of the solution was measured near 5.0 using pH meter. By
adding suitable amount of diluted Hydrochloric acid, the pH of the solution was decreased to 3.2
which is more than sufficient for the crystallization process. The resulting solution was filtered
using a Whattman filter paper and the beaker containing the filtrate was kept in a dust free
environment for crystallization.Fig.1 gives the reaction scheme for the formation of title
compound. After a period of 20 days, yellow colour crystals of title compound were obtained. The
purity of the synthesized crystal was improved considerably by repeating the recrystallization
process three times. Fig.2 shows the as-grown single crystal of the title compound.

3. Characterization techniques
The single crystal XRD data of the grown crystal was obtained using a Enraf Nonius
CAD4-MV31 single crystal X-ray diffractometer with MoKα(0.7107 Å) radiation at room
temperature. The ORTEP view of the molecule was drawn at 50% probability thermal
displacement ellipsoids with the atom numbering scheme. The crystal structure was solved by a
direct method with the SHELXS-97 program[19,20]. The UV-vis-NIR spectrum was recorded in
the range of 200-800nm using Perkin-Elmer Cary 5E spectrometer. The FT-IR spectrum of the title
1
compund was obtained using JASCO FT-IR 410 spectrometer by the KBr pellet method. The H
and 13C NMR spectra of the title compound were recorded using DMSO as a solvent on a Brucker
1
AVANCE III 500 MHz (AV 500) instrument at 23oC (300 MHz for H NMR and 75 MHz for
13CNMR) to confirm the molecular structure. The TG-DTA of the title compound has been
analysed by using a TGA Q50V20.13 Build 39 Perkin-Elmer Diamond TG-DTA instrument. A
platinum crucible was used for heating the sample and analysis was carried out in an atmosphere of
nitrogen at a heating rate of 100C/min in the temperature range of 23-6000C. The dielectric
property was studied using a HIOKI 3532-50 LCR HITESTER by varying the temperature in the
frequency range from 50Hz to 5 MHz. Photoconductivity measurements were made on the grown
crystal using KEITHLEY 485 picoammeter. The SHG efficiency of the grown crystal was
determined with help of modified Kurtz and Perry technique using Nd:YAG laser with pulse
repetition rate of 10Hz and wavelength 1064nm.
4. Results and Discussions
4.1. Single crystal XRD analysis
Single crystal X-ray measurements were made at 293 K using suitable data collection. In the
single crystal XRD data collection, 9,494 reflections were recorded in the range of 2.68o to 24.99o
of which 1887 reflections were unique reflections. The data reveal that the synthesized crystal
belongs to the monoclinic crystal system with space group P21/n. The lattice parameters obtained
are a=11.2650(2) Å, b=6.669 (10) Å, c=14.8880(3) Å, α=90º, β=106.98(10)º and γ=90º. The unit

cell volume is 1069.67(3) Å3 and Z=2. The crystallographic data and structure refinement
parameters are given in Table 1. Table 2 presents the crystallographic data of title compound and
other picrate crystals for comparison. Since the grown crystal is a new compound (CCDC
no.941605), the crystallographic data of this compound are different from those of other picrate
crystals.
The title compound crystallizes in monoclinic system with space group P21/n. The asymmetric
unit consists of one picrate anion and half piperazinium cation. The two halves of piperazinium
cations are related through crystallographic centre of inversion. Fig.3 shows the ORTEP
representation of the molecule with atom numbering scheme. The crystalline packing (Fig.4)
shows that piperazinium cations are interposed between two centrosymmetric pairs of picrate
anions. The anion pairs are hydrogen bonded (N-H...O) to the cations and the motif is connected
to its b-translation equivalents to form a one dimensional hydrogen bonded chain parallel to b-
axis.
The single crystal X-ray structure of the proton transfer complex of title compound shows the
presence of protonated piperazine cation and deprotonated picrate anion for intermolecular
hydrogen bonding associations as shown in ORTEP Fig.3 and also in Table 3.
The selected bond lengths and bond angles are presented in Table 4. The loss of a proton
from picric acid is confirmed by the lengthening of the C-O bonds. The bond lengths and bond
angles of the picrate anion show the characteristic values, with C6-C1=1.439(2) Å and C6-
C5=1.4369(19) Å distances longer than the normal aromatic C-C values 1.40 Å. These differences
are attributed to the loss of a hydroxyl proton at O7 which leads to the conversion from the neutral
to the anionic state. The crystal packing diagram along Y-axis is shown in Fig.4.
The repulsive interactions of the deprotonated oxygen atom O7 with the electron
withdrawing group NO2 attached to the ortho positions of O7 are responsible for the shortening of
the C1-C2=1.3692(19) Å andC4-C5=1.367(2) Å bonds. The repulsive interactions also have a role
to play the significant differences in the internal C-C-C angles within the ring joining the NO2

groups C6-C5-C4=124.58(13)ºand C6-C1-C2=124.19(12)º.TheC5-C6-C1=112.03(12)º angle
joining the deprotonated hydroxyl group is significantly smaller than the expected angle (120 º).
On comparison of bond lengths of C6-C1=1.439(2) Å,C6-C5=1.4369(19) Å,C1-C2=1.3692(19) Å,
C4-C5=1.367(2) Å and C6-O7=1.2580(16) Å with normal bond lengths of C-C,C=C and C-O, it is
found that the C6-C1,C6-C5(1.5 Å) have single bond character and C1-C2,C4-C5 (1.39 Å) have
double bond character. The C-O (1.21 Å) also carries double bond character. This indicates that
the crystal possesses more quinonoid character than benzenoid character.
Table 5 shows the torsional angles data for the grown crystal. The torsion angles of O3-N2-
C5-C6, O1-N1-C1-C6 are found to be 34.5(2) ºand 25.1(2) º respectively. From the torsion angles
data, it has been found that the ortho nitro groups are commonly involved in hydrogen bonding
interactions.
The twist angles of the three nitro groups attached to the benzene ring are[O2-N1-
O1=122.75(13) º], [O3-N2-O4=123.46(14) º], and [O6-N3-O5=123.16(13) º].The twisting nature
of the nitro groups in picrate ions shows that the ortho nitro groups are away from the plane of the
benzene ring, possibly as a result of steric hindrance with the phenolic group at C6.
The packing of molecules in the crystal lattice is determined by conventional and
unconventional C-H…O hydrogen bonds. In addition to the conventional hydrogen bonds, the
short C-H….O intermolecular contacts between C4-H4 or C5-H5 and nitro group are also
observed. This is an important feature in all- aromatic picrate complexes [23].
4.2. FTIR analysis
The FTIR spectrum of the title compound is shown in Fig.5. The characteristic absorption
bands were recorded in the spectral range 4000-400 cm-1 in order to confirm the presence of
functional groups in the crystal. The presence of NO2, N-H and C-H is confirmed with the
assigned wavenumbers from the spectrum. The 3318 cm-1 and 3068 cm-1 absorption peaks are due
to N-H asymmetric and symmetric stretching vibrations. The absorption peaks at 3068 cm-1 and
2841 cm-1 are due to C-H asymmetric and symmetric stretching vibrations. The presence of peaks

corresponding to 1624 cm-1 and 1273 cm-1 are due to C=C stretching vibrations and the presence
of phenolic ‘O’ atoms. The peaks at 1436 cm-1 and 1321 cm-1are due to asymmetric and
symmetric stretching vibrations of the nitro group. The lower peaks at 848 cm-1 and 787cm-1 are
due to deformation and wagging of nitro groups respectively while 615 cm-1 and 589 cm-1 are due
to rocking vibration of nitro group. The observed spectral data and their assignments for title
compound are tabulated in Table 6. The functional groups of the grown material are thus
identified.
4.3. NMR spectroscopy
The 1H NMR and 13C NMR spectral analyses are the two important analytical techniques used
to study the molecular structure of title compound. Fig..6a shows the structure of title compound
with different number of protons and carbon chemical environments involved in the structure.
4.3.1. 1H NMR spectrum
1
Fig.6b shows the recorded H NMR spectrum of grown crystal which shows five different
signals due to five distinct proton environments including solvent signal. The peaks at δ 2.3ppm
corresponds to solvent peaks. The normal peak corresponding to CH2 (C7 and C8) protons will lie
+
in the region of δ 4-5ppm. Since CH2 is shielded due to NH2 proton CH2 proton has increased its
absorbing power of the higher order magnetic field for the precessional motion of the nucleus. The
energy difference caused shifts the peak signal from δ 4-5ppm to δ 2.5ppm. Hence, the shifting of
the peak signal towards lower value confirms the shielding effect.
+
The signal at δ 6.8ppm assigned to NH2
protons in piperazine are deshielded due to the
decreasing absorbing powers of the applied magnetic field by N and O atoms. As a result, δ value
is increased from 2-3ppm to 6.8ppm. Hence the signal at δ 6.8ppm confirms the deshielding effect
+
of N and O atoms on NH2 proton. The peak at δ 7.5ppm is due to the aromatic protons in the
picrate moiety of the crystal having the same kind of chemical environment attached with C2 and

C4 carbon atoms. The peak at 9.961ppm reveals the interaction between picric acid and piperazine
which leads to desheilding of phenolic proton in picric acid.
4.3.2. 13 C NMR spectrum
Fig.6c shows the 13C NMR spectrum of the title compound. The appearance of 6 distinct
carbon signals in the spectrum including the solvent peak unambiguously confirms the molecular
structure of the title compound. The signal at δ 150.88 ppm has been assigned to the C6 aromatic
carbon (C-O) atom in the picrate ion. The signal at δ 133.76ppm is assigned to C5 and C1 carbon
attached to nitrogen atoms (C-N) in the picrate moiety having same carbon environments and the
δ 144.31ppm corresponds to C3 while δ 124.58ppm corresponds to C2 and C4 aromatic carbon
atoms of picrate anion. The signal at δ 121.50 ppm shows C7 and C8 of piperazinium cation. The
solvent peaks are shown at δ 40.08 ppm. It is concluded that the spectrum provides the useful
information about the various types of carbon atoms involved in the molecular structure of the title
compound.
4.4 UV-vis- NIR spectral analysis
The UV-vis-NIR absorption spectrum of the grown crystal was recorded in the wavelength
range of 200-800 nm (Fig.7a). The higher intensity of the absorption band observed in the UV
region may be due to conjugated systems present in the grown material. The absorption is very
low near infrared region and the entire visible region with cut-off wavelength 240nm.
However,100% transmission is observed from 532nm onwards. The optical band gap (Eg) was
evaluated using Tauc's relation given by
αhν = A(Eg - hν)2
(1)
where α is the absorption coefficient, A is a constant, Eg is the optical band gap, h is the Planck
constant and v is the frequency of the incident photons. The value of band gap energy was

estimated from the graph between (αhν) 2 and hν (Fig.7b) by extrapolating the linear portion of the
curve to zero absorption. The optical band gap was measured as 2.63 eV. The higher value of
optical band gap suggests that material is dielectric in nature. Only the dielectric material will
have wide transparency. The material with wide transparency is required for the fabrication of
optical devices.
4.5. Thermal analysis
The Thermogravimetric (TG) and Differential thermal analysis (DTA) were carried out in the
-1
nitrogen atmosphere at a heating rate of 10oC min from 0 ºC to 600 ºC. It is observed from TG
curve that the weight loss is negligible (0.70%) at 166ºC and the major weight loss starts from
304.1ºC onwards. This observation which is confirmed by the endothermic peak of DTA analysis
at 304.1ºC.
Even though the weight loss starts at 166ºC, the major weight loss occurs from 304.1 ºC onwards.
Hence, the crystal can be used in devices with more thermal stability up to 304.1 ºC. The weight
loss at 166oC is due to evaporation of solvent molecules. The decomposition at 600 ºC gives a
residue of 21.90% and this is due to the carbon residue. The sharpness of the peak shows the good
degree of crystalline quality of the crystal [26, 27]. The title compound has fairly high melting
point. Table.7 shows the comparison of thermal stability (melting point) of the grown crystal with
that of other picrate crystals.
4.6 Dielectric studies
The dielectric constant and dielectric loss were measured in the frequency range from 50 Hz to
5 MHz at various temperatures. Good quality crystal was selected for dielectric studies. The
surface of the sample was coated with silver for good electrical contact. The dielectric constant
and dielectric loss were calculated using the formula,
Dielectric constant
and
ɛ'=Cd/Aɛo
(2)
Dielectric loss
tanδ=ɛD
(3)
r

where C is the capacitance, d is the thickness, A is the area of the crystal and D is the dissipation
factor.
The plots of dielectric constant versus frequency and dielectric loss versus frequency are
shown in Figs.9a and 9b at 323 K, 373 K and 423 K. From the graph, the dielectric constant is
found to decrease with increase in frequency. The large values of dielectric constant at low
frequencies are due to the presence of space charge polarization [35]. The decrease in the value of
dielectric constant with frequency is due to the fact that the frequency of electric charge carriers
cannot follow the alternation of the AC electric field applied beyond a certain critical frequency
[36]. The very low value of dielectric constant at higher frequencies is important for the
fabrication of ferroelectric, photonic and electro-optic devices [37]. The low values of dielectric
constant and dielectric loss at high frequencies suggest that grown crystal contains minimum
density of defects with high optical quality [38].
4.7 AC conductivity studies
The AC conductivity of grown crystal was evaluated using the formula
σac= 2πf ɛo ɛr tanδ
(4)
where ɛo is the permittivity of the dielectric constant, ɛr is the dielectric constant, f is the
frequency of ac applied and tanδ is the dielectric loss. Fig.10a shows the variation of ac
conductivity with frequency. The ac conductivity is zero up to 1MHz and starts increasing from 1
MHz onwards. This is due to the fact that the relaxation time of charge carriers is not matching
with the time period of the applied ac field up to 1 MHz and so the conductivity of the material is
almost zero. The variation of ac conductivity with temperature follows the Arrhenius plot as
σac = σoexp(-Ea/kT)
(5)

where Ea is the activation energy, k is the Boltzmann constant and T is the temperature (in
kelvin). Fig.10b shows the plot of ln σac versus temperature. As the temperature is increased, the
ac conductivity is found to increase. When the temperature is increased, the thermal energy
sufficiently increases to enhance the movement of charge carriers for increasing the ac
conductivity. The slope of the plot gives the activation energy required to aid the conduction
process for the charge carriers. The value is found to be 0.1795 eV and the lower value of
activation energy establishes that the grown crystal contains less number of defects.
4.8 Photoconductivity studies
The photoconductivity measurements were carried out for the grown crystal using Keithley 485
picoammeter. Initially, the sample was kept away from any other radiations. Dark current was
measured by connecting the sample in series with a DC power supply and picoammeter. Electrical
contacts were made on the sample using silver paint. The photocurrent for the same sample was
measured by exposing it to the radiation from a halogen lamp containing iodine vapor by focusing
a spot of light on the sample with the help of a convex lens. The applied field was increased from
100 to 4000 V/cm and the corresponding photo current was recorded. The photo current and dark
current were plotted as a function of the applied field. Fig.11 shows the variation of both the dark
current and photo current of the sample with applied voltage. From the Fig.11, both the dark and
photocurrent are seen to increase linearly with the applied field. The photocurrent is found to be
less than the dark current for every applied electric field. This phenomenon is known as negative
photoconductivity. However, the negative photoconductivity in this case may be due to the
reduction of the number of charge carriers and their lifetime in the presence of radiation[39][40].
In Stockman model, a two level scheme is proposed to explain negative photoconductivity in
semiconductors and the details are reported [41]. For a negative photoconductor, forbidden gap
holds two energy levels in which one is placed between the Fermi level and the conduction band
while the other is located close to the valence band. The second state contains traps

(recombination centres) to capture electrons and holes [42]. As a result, the number of mobile
charge carriers is reduced giving rise to negative photoconductivity..
Even though, the present material shows negative photoconductivity, it is capable of inducing
dipoles due to intense incident radiation to reveal the nonlinear behavior of the material. It is
found that the material shows SHG efficiency comparable with that of standard KDP material.
4.9 SHG efficiency measurements
The SHG efficiency of the grown crystal was measured by modified Kurtz and Perry technique
using Nd: YAG laser with pulse repetition rate of 10Hz and wavelength 1064 nm. The sample was
ground well and tightly packed in a micro capillary tube. The relative SHG efficiency of the grown
crystal was measured by comparing the SHG output with the help of a standard KDP (Potassium
dihydrogen phosphate) sample of same particle size. The relative efficiency was found to be 0.8
times that of standard KDP. SHG was confirmed by the emission of green radiation (532nm) from
the crystal. On a molecular scale the extent of charge transfer (CT) across the NLO Chromophore
determines the level of SHG efficiency. Even though the grown crystal belongs to centrosymmetric
group, it exhibits considerable amount of NLO behavior. .Rieckoff et al [43], Ghazaryan et al[44],
Shakir et al [45] and Dhanabal et al[32] have studied the SHG efficiency of some centrosymmetric
crystals R,S-Serine, diglycine picrate ,glycine picrate and 2-methylimidazolinium picrate crystals.
In the grown crystal, the strong proton donor picric acid transfers a proton to the strong
proton acceptor piperazine. Intermolecular hydrogen bonding is formed between the hydrogen of
the protonated nitrogen atom of piperazine and the negatively charged oxygen atom of the picrate
anion. In the present case, the donor–acceptor strength is considerably high due to the
intermolecular hydrogen bonding. The NLO behaviour of the title compound may be due to the
presence of intermolecular hydrogen bonding. This indicates that the synthesized title compound
can be used as a better NLO material.

5. Conclusion
Single crystals of Piperazine-1,4-diium bis 2,4,6-trinitrophenolate were synthesized and
crystallized using piperazine and picric acid as starting materials by slow evaporation method. The
structure of the grown crystal was solved using SHELXS-97 program. It is observed from the
crystallographic data that the grown crystal belongs to monoclinic system with P21/n space group.
The high value of optical band gap and the wide transmission range were ascertained using UV-
vis-NIR spectrum. The presence of various functional groups and protons and carbon atoms of
various chemical environment present in the grown crystal was confirmed by FT-IR and NMR
spectral analysis. Thermal studies reveal that the grown crystal is thermally stable up to
304.1°C. Dielectric studies establish the dielectric behaviour of the grown crystal which is
important for the study of NLO property. The crystal possesses SHG efficiency 0.8 times than that
of KDP. Hence, the grown single crystal is one of the useful organic crystals with NLO
applications.

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charge at www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic
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email: deposit@ccdc.cam.ac.uk].
17

Figure captions
Fig.1 Reaction scheme of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
Fig.2 As grown single crystal of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
Fig.3 ORTEP diagram of the Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
Fig.4 The packing of the molecules, viewed along ‘b’ axis
Fig.5 FT-IR spectrum of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
Fig.6a Structure of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
6b 1H NMR spectrum of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
6c 13C NMR spectrum of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
Fig.7a UV- visible-NIR spectrum of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
7b Plot of (αhν)2 versus photon energy
Fig.8 TGA and DTA curve of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
Fig.9aVariation of dielectric constant of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
crystal as a function of frequency at different temperatures.
9b Variation of dielectric loss of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
crystal as a function of frequency at different temperatures
.
Fig. 10a Plot of ac conductivity of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate versus
frequency.
10bPlot of ac conductivity of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate versus
temperature.
Fig .11 Field dependent photoconductivity of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
single crystal
18

Fig.1. Reaction scheme of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
Fig.2.Grown single crystal of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
19

Fig.3. ORTEP diagram of the Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
20

Fig.4. The packing of the molecules, viewed along ‘b’ axis.
21

Fig.5. FT-IR spectrum of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate .
22

Fig.6 (a) Structure of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
.
23

Fig.6 (b) 1H NMR spectrum of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
24

Fig.6 (c) 13C NMR spectrum of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
25

Fig.7. (a) UV- visible-NIR spectrum of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
26

50000
40000
30000
20000
10000
0
2.63 eV
1
2
3
4
5
6
7
hυ(eV)
Fig.7.(b) Plot of (αhν)2 versus photon energy
27

Fig.8. TGA and DTA curve of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
28

110
100
90
80
70
60
50
40
30
20
323K
373K
423K
2
3
4
5
6
7
log f
Fig.9.(a) Variation of dielectric constant of Piperazine-1, 4-diium bis 2,4,6-trinitrophenolate
crystal as a function of frequency at different temperatures.
29