Entry of chiral phthalimides with significant second order nonlinear optical and piezoelectric properties

Article abstract of DOI:10.1039/c3ra41089g

Three new chiral phthalimides have been synthesized and characterized. Phthalimides (1-3) possess an acentric structure as revealed by structural investigation. Compounds 1 and 2 crystallize in an orthorhombic system with the space group P2₁2

Full text of DOI:10.1039/c3ra41089g

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Entry of chiral phthalimides with significant second
order nonlinear optical and piezoelectric properties3
Cite this: RSC Advances, 2013, 3,
14750
Anil K. Singh,a Ram Kishan,b N. Vijayan,c V. Balachandran,d Taruna Singh,b Hemandra
K. Tiwari,a Brajendra K. Singha and Brijesh Rathi{*a
Three new chiral phthalimides have been synthesized and characterized. Phthalimides (1–3) possess an
acentric structure as revealed by structural investigation. Compounds 1 and
2 crystallize in an
orthorhombic system with the space group P212121, however the monoclinic system with the chiral
…
space group P21 is observed for 3. The presence of C–H O hydrogen bonds in 1–3 facilitates the
construction of several supramolecular structures. Helical structural motifs are also observed. The
maximum value of hyperpolarizability (b), 159.9446 6 10230 esu calculated for compound 3 is several
times greater than that of urea. On the other hand 1 and 2 have hyperpolarizabilities of 10.8063 6 10230
and 121.9519 6 10230 esu, respectively. The polycrystalline samples of 1–3 were assessed for a second-
harmonic generation response, which was found to be 8.8, 10.2 and 9.7 mV respectively. Further,
compounds 1–3 showed d33 values of 0.93, 1.97 and 1.88 pC N21 respectively. The present investigation
demonstrates chiral phthalimides as effective contenders for nonlinear optical and piezoelectric properties.
Received 6th March 2013,
Accepted 30th May 2013
DOI: 10.1039/c3ra41089g
www.rsc.org/advances
in the area of information technology, optical storage and
information processing among other areas.6 Hence, the
Introduction
The search for a new generation of materials with greater
technological applications, especially nonlinear optical proper-
ties is being addressed successfully with the aid of crystal
packing arrangements.1,2 Extensive research on organic and
metal–organic frameworks has led to numerous classes of
second harmonic generation (SHG) and also synthons for
supramolecular assemblies.1,3,4 Specifically, the designing and
construction of organic molecules with nonlinear optical and
piezoelectric properties possessing better transparency is a
rapidly growing field. Organic materials are of interest owing
to their easy tailoring, high solubility and informal biocompat-
ibility over pure inorganic materials. Nonlinear optical efficacy
of organic materials is governed by their acentric nature, high
hyperpolarizability (b) and their helical structural motifs.5 The
fabrication of acentric organic crystals has attracted enough
consideration from scientists because of their wide application
discovery of new organic molecules with acentric structures
is the most crucial component in advancing technology.
Even in recent years the rational design and preparation of
organic crystals with an acentric structure has been a most
challenging and laborious task. However, the problem has
been tackled by employing several approaches, mainly the use
of functionalized chiral molecules to generate new acentric
crystals.1b,7,8 Not enough reports are available on organic
acentric crystals possessing high nonlinear optical potential.5b
The presence of one or more chiral centers in a molecule helps
in developing the acentric structure and this strategy is
employed to obtain novel acentric materials.9 We have been
interested in extending the concept of chirality in phthali-
mides with the aim of exploring their structural aspects and
…
solid state properties. The presence of C–H O hydrogen
bonding in several phthalimides supported their great
significance in crystal engineering and allowed the building
of supramolecular-structures.10 In this paper, we report the
synthesis, spectroscopic characterization and structural inves-
tigation of functionalized chiral phthalimides (1–3). An
economic and convenient synthesis is reported and shown in
Scheme 1. The strategy of introducing chirality enables us to
obtain acentric organic crystals.
aBio-organic Research Laboratory, Department of Chemistry, University of Delhi,
Delhi-110 007, India. E-mail: brathi@svc.ac.in; Fax: +91-11-24118535
bDepartment of Chemistry, University of Delhi, Delhi-110 007, India
cCSIR-National Physical Laboratory, Dr K. S. Krishnan Road, New Delhi-110 012,
India
dPG & Research Department of Physics, Aringer Anna Government Arts College,
Musiri-621 211, India
Electronic supplementary information (ESI) available: General consideration,
3
We also report polarizability and hyperpolarizability (b)
calculations, which are further substantiated by the second
order NLO response of newly prepared molecules. The
significant properties of hyperpolarizability, second order
NLO response and piezoelectric properties measured for 1–3
TGA plots, NMR spectra and X-ray crystallographic details for compounds 1–3
having CCDC No. 895512-14. For ESI and crystallographic details and additional
data in CIF See DOI: 10.1039/c3ra41089g
{ Current address: Department of Chemistry, Sri Venkateswara College,
University of Delhi, New Delhi-110021, India.
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Scheme 1 Reagents and conditions: a) SOCl2, DMF, 90 uC, 2 h; b) EtOAc, TEA, RT, 2 h.
advocate their entry as important agents for technological
applications.
symmetry.11 It can be given in the lower tetrahedral format. It
is obvious that the lower part of the 3 6 3 6 3 matrix is a
tetrahedral. The components of btot are defined as the
coefficients in the Taylor series expansion of the energy in
the external electric field. When the external electric field is
weak and homogeneous, this expansion becomes:
Computational details
The first hyperpolarizability (btot) and related properties like
electric dipole moment (mtot), and mean polarizability (atot) of
1–3 are calculated based on a finite field approach. The
computed results by density functional quantum chemical
method with a 6-311++G(d,p) basis set are summarized in
Table 1. To calculate all the electric dipole moments and the
first hyperpolarizabilities for the isolated molecules, the origin
of the Cartesian coordinate system (x,y,z) = (0,0,0) was chosen
at the centre of mass of 1–3. In the presence of an applied
electric field, the energy of a system is a function of the electric
field. First hyperpolarizability is a third rank tensor that can be
described by a 3 6 3 6 3 matrix. The 27 components of the 3D
matrix can be reduced to 10 components due to the Kleinman
0
1
1
E~E {maFa{ = aabFaFb{ = babcFaFbFcz::::::
2
6
Where E0 is the energy of the unperturbed molecules, Fa is
the field at the origin ma, aab and babc are the components of
dipole moment, polarizability and the first hyperpolarizability,
respectively. The total static dipole moment m, the mean
polarizability atot, and the mean first hyperpolarizability btot
using the x,y,z components are defined as:
,
ꢀ
ꢁ
1
=
2
m
tot~ m2xzm2yzm2z
a
xxzayyzazz
atot
~
3
Table 1 The electric dipole moment m (D), the average polarizability atot and the first hyperpolarizability btot of compounds 1–3
Parameters
1
2
3
mx
my
mz
mtot
axx
axy
ayy
axz
ayz
20.4772
3.5577
22.3447
4.2782
2107.5749
6.3287
2130.637
24.5720
3.0273
1.1073
0.9830
22.6007
2.9927
2108.2113
26.4977
2152.2904
2.0965
21.7334
21.0093
22.6580
3.3299
2113.4885
23.585
2164.0771
21.2792
1.3812
23.7465
azz
2140.0213
126.0777 6 10224
218.4676
235.1465
25.6707
22.2701
20.4911
2.5461
4.2231
2151.8510
2137.4509 6 10224
152.3067
2.9313
218.6060
44.6063
11.3165
6.0577
21.0832
222.1001
23.4872
2162.1268
atot (esu)
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
byyz
bxzz
byzz
bzzz
btot (esu)
2146.5641 6 10224
2199.6724
1.1339
18.6896
239.3774
15.9238
0.3823
23.4222
27.0008
5.9294
14.0224
11.2541
27.1690
210.5563
210.5778
10.8063 6 10230
121.9519 6 10230
159.9446 6 10230
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…
Fig. 1 (a) Molecular structure of 1 at 40% probability level. (b) A view of the hydrogen bonded network stabilized by C–H O hydrogen bonds. (c) Space filling model
of the packing diagram forming the supramolecular architecture (viewed along the b-axis). (d) Space filling model of the packing diagram (viewed along the a-axis).
1
ꢀ
ꢁ
=
2
b
tot~ bx2zb2yzb2z
The reaction afforded 1–3 as colorless solids in good yield. The
composition of new compounds 1–3 was confirmed by
analytical and spectroscopic techniques. The presence of
functional groups and their vibrational mode was studied by
FTIR spectroscopy. The two characteristic bands at 1712 and
1648 cm21 in compound 1, 1718 and 1647 cm21 in compound
2 and 1718 and 1645 cm21 in compound 3 correspond to two
types of carbonyl stretching frequencies. Bands at higher
frequencies are stronger and correspond to carbonyl groups
present in the isoindoline ring. Bands at lower frequencies
correspond to the carbonyl group attached to the cyclic amine.
In the 1H NMR spectrum, the peak of the chiral proton was
obtained as a double doublet at d values ranging from 4.99 to
5.30 with J values of 4.4 and 11.72 Hz for 1, 6.60 and 9.56 Hz
for 2 and 5.80 and 10.24 Hz for 3. Peaks for protons
corresponding to the heterocyclic ring (pyrrolidine and
piperidine) were observed as two bunches. Four N–C protons
were assigned as multiplets ranging from d 3.67 to 3.42 and
the remaining protons were assigned upfield as multiplets
ranging from d 1.93 to 1.39. Methylene protons adjacent to the
chiral carbon of compounds 1, 2 and 3 were found in the range
bx = bxxx + bxyy + bxzz
by = byyy + bxxy + byzz
bz = bzzz + bxxz + byyz
Results and discussion
Synthesis and spectroscopic characterization
We have designed phthalimides possessing chirality and
functionalized them with heterocyclic amines with the
expectation of their acentric structure. Compounds (1–3) were
prepared from the reaction of N-phthaloyl-L-amino acids with
corresponding cyclic amines in the presence of triethylamine.
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Fig. 2 (a) Molecular structure of 2 at 40% probability level. (b) A view of hydrogen bonded network. (c) Space filling model of the packing diagram (viewed along the
b-axis). (d) A view of the hydrogen bonded network (viewed along the a-axis).
from d 2.55 to 1.75. Peaks of aromatic protons of the
isoindoline ring were found from d 7.81 to 7.64. All the
protons of the benzylic nucleus ranged from d 7.18 to 7.11. The
peaks were assigned with the aid of 2D NMR spectra of all
around the central carbon atom is tetrahedral but not a regular
one. The O1 of the phthalimide ring is involved in bifurcated
intermolecular hydrogen bonding with H17B and H2B of two
different adjacent molecules. The angles between C17–
…
…
three compounds (see ESI ). The solid-state UV-Visible spectra
H17B O1 and C2–H2B O1 are 144.4u and 175.2u, respectively
which suggests the former one has moderate and the latter
one has very strong intermolecular hydrogen bonding. The
oxygen atom, O3 of 1 is involved in very weak intermolecular
hydrogen bonding with H10 of the neighboring molecule with
a bond angle 129.3u. In compound 1 each building block is
involved in intermolecular hydrogen bonding with three
neighboring building blocks, and the extension of such
interactions generated a zig-zag 2D sheet when viewed along
the b-axis (Fig. 1b and c). Each tetrahedral unit combined to
form a closed layer type sheet when viewed along the a-axis.
Compound 2 crystallized in the orthorhombic system with a
P212121 space group. The molecular structure and self-
assemblies of 2 are shown in Fig. 2. The geometry of the
3
of 1–3 showed lmax at y240 nm indicating their transparency
in the visible region.
Crystal structure investigation
Suitable colorless crystals of 1–3 were grown from acetonitrile
and subjected to single crystal X-ray diffractometry to explore
their solid-state features. Compound 1 crystallized in the
acentric orthorhombic system with a P212121 space group. The
molecular structure and self-assemblies of 1 are depicted in
Fig. 1. The chiral central carbon C1 is surrounded by four
different substituents, a phthalimide molecule, an isobutyl
molecule, and a carbonyl group, which is further attached to a
puckered pyrrolidine unit and a hydrogen atom. The geometry
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Fig. 3 (a) Molecular structure of 3 at 40% probability level. (b) Space filling model of the packing diagram showing the helical motifs (viewed along the c-axis). (c) A
view of the hydrogen bonded network. (d) Space filling model of the packing diagram (viewed along the a-axis).
chiral central carbon C1 was found to be similar to compound
1. Three imide oxygen atoms are involved in intermolecular
hydrogen bonding with neighboring molecules. Atom O1 of 2
is involved in intermolecular hydrogen bonding with H12 of
the neighboring molecule and the bond angle between C12–
hydrogen bonding. Atom O3 of compound 2 is also involved in
bifurcated hydrogen bonding with H14 and H18A of two
different neighboring molecules. The bond angle between
C14–H14 O3 and C18–H18A O3 was found to be 142.2 and
144.5u respectively. Both the values suggest the presence of
strong intermolecular hydrogen bonding. The extension of the
above hydrogen bonding in 2 dimensions leads to the
formation of a 2D sheet like structure when viewed along the
b-axis (Fig. 2b and c).
…
…
…
H12 O1, 174.9u, suggests very strong intermolecular hydrogen
…
bonding between them. Bifurcated C–H O intermolecular
hydrogen bonding was observed between O2 and H6/H21A of
two different neighboring molecules. The bond angle values of
…
…
C6–H6 O2 (137.9u) and C21–H21A O2 (155.9u) suggest the
Compound 3 crystallized in the monoclinic system with a
P21 space group. The molecular structure and self-assemblies
former has moderate and the latter has strong intermolecular
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10.2 and 9.7 mV respectively. A significant value of SHG of 10.2
mV was recorded for compound 2 and is comparable with the
13.6 mV observed for KDP. Further, phthalimides (1–3) were
also evaluated for piezoelectric response and d33 values are
0.93, 1.97 and 1.88 pC N21 respectively.
Table 2 Second Order NLO and d33 response
SHG Response (mV)
KDP (mV)
d33 (pC N21
)
1
2
3
8.8
10.2
9.7a
13.6
13.6
21a
0.93
1.97
1.88
Thermal stability analysis
a
Input beam energy: 1.3 mJ per pulse.
In order to determine the thermal stability, thermogravimetric
analysis (TGA) of 1–3 was conducted and the plots are given in
the ESI. The onset of the decomposition of compound 1 starts
3
of 3 are depicted in Fig. 3. Compound 3 has a planar six
membered nitrogen containing piperidine moiety. The geo-
metry around the central carbon atom is the same as in
compound 1 and 2. Three imide oxygen atoms are involved in
intermolecular hydrogen bonding with neighboring mole-
cules. The O1 of 3 is involved in intermolecular hydrogen
bonding with H20B of the neighboring molecule and their
at 200 uC after that drastic weight loss is observed up to 300 uC.
Compound 2 is relatively stable up to 210 uC, a sharp weight
loss is observed up to 360 uC. Compound 3 is most stable, the
onset of the decomposition starts at 230 uC and after that
weight loss is observed up to 360 uC. Out of these observations
we can conclude that the compounds are fairly stable.
…
angle value 166.5u between C20–H20B O1 suggests very
strong intermolecular hydrogen bonding. Atom O2 of 3 is
involved in intermolecular hydrogen bonding with H18B of the
piperidine moiety of a different neighboring unit. The bond
angle value, 126.8u for C18–H18B O2 suggests weak inter-
molecular hydrogen bonding. Atom O3 of 3 is also involved in
Conclusions
In summary, we have discovered chiral phthalimides as new
acentric organic crystals with substantial second order NLO
activity. The incorporation of chirality into the phthalimides
facilitated the production of acentric crystals. Our structural
investigations indicated that these phthalimides are robust
and encouraging synthons for the formation of hydrogen-
bonded frameworks with helicity. Compound 2 exemplifies a
promising candidate for future study in the field of second
order nonlinear optics and piezoelectricity. The present study
establishes a simple and suitable route for the production of
new chiral organic materials enriched with technological
applications.
…
bifurcated hydrogen bonding with H6 and H13 of two different
…
neighboring molecules. The bond angle between C6–H6 O3
…
and C13–H13 O3 are 140.9 and 158.3u respectively, which
indicates the presence of strong intermolecular hydrogen
bonding. The extension of the above hydrogen bonding in 2
dimensions leads to the formation of a 2D sheet like structure
when viewed along the a-axis (Fig. 3c and d).
Hyperpolarizability calculations
The DFT/6-311++G(d,p) calculated first hyperpolarizability of
compounds 1, 2 and 3 are 10.8063 6 10230, 121.9519 6 10230
and 159.9446 6 10230 esu, respectively. The calculated values
of mtot, (4.2782, 2.9927 D, 3.3299 D), atot values are 126.0777 6
10224, 2137.4509 6 10224 and 2146.5641 6 10224 esu and
btot values are 10.8063 6 1023, 121.9519 6 10230 and
159.9446 6 10230 esu for compounds 1, 2 and 3, respectively.
From these results, the hyperpolarizability value of compound
3 is higher than the other molecules, which is 428.9 times
greater than that of urea (the mtot, atot, and btot of urea are
1.373 D, 3.8312 6 10224 esu and 0.37289 6 10230 esu
obtained by the B3LYP/6-31G(d) method.12 The results
indicate that compound 3 is a good candidate as a NLO
material. As can be seen from the btot value for this molecule,
the larger value of first hyperpolarizability corresponds to the
lower HOMO–LUMO gap. This correlation is reported in the
literature.13 In addition, the maximum btot value may be due to
p-electron cloud movement from donor to acceptor which
makes the molecule highly polarized and the intramolecular
charge transfer (ICT) possible. The presence of ICT is
confirmed with vibrational spectral analysis.
General procedure for synthesis of 1–3
N-Phthaloyl-L-amino acids were prepared following the litera-
ture procedure.14 To N-phthaloyl-L-amino acid (3.83 mmol)
two drops of DMF were added and heated up to 40–50 uC
followed by the slow addition of freshly distilled thionyl
chloride (0.5 mL). The contents were heated at 90 uC for 2 h.
The reaction mixture was cooled to room temperature and
kept in an ice bath. Cyclic amine (4.59 mmol, dissolved in 20
mL of ethyl acetate) and triethylamine (1.0 mL) were added
subsequently to the reaction mixture and the contents were
stirred at room temperature for 2 h. The reaction mixture was
concentrated under reduced pressure and extracted into ethyl
acetate. The organic layer was dried over anhydrous Na2SO4
and concentrated under reduced pressure. The residue thus
obtained was purified by silica gel chromatography (9 : 1–1 : 1
petroleum ether/ethyl acetate gradient) to afford the title
compounds as white solids.
2-(4-Methyl-1-oxo-1-(pyrrolidin-1-yl)pentan-2-yl)isoindoline-
1,3-dione (1). Yield = 78%; Melting point: 115 uC (DSC); [a]D20
247.2; FTIR (KBr) nmax (cm21): 2962, 2949, 2866, 1712, 1648,
1466, 1425, 1380, 1057, 719, 530, 498; 1H NMR (400 MHz,
CDCl3): d 7.82 (2H, m), 7.70 (2H, m), 5.00 (1H, dd, J = 11.72, 4.4
Hz), 3.47 (4H, m), 2.58 (1H, m), 1.93 (2H, m), 1.84 (2H, m), 1.76
(1H, m), 1.55 (1H, m), 0.94 (6H, t, J = 5.88 Hz) ppm; 13C NMR
(100 MHz, CDCl3): d 168.0, 167.6, 134.0, 131.6, 123.3, 51.5,
Optical and piezoelectric properties
In order to validate our computational results, the crystalline
forms of 1–3 were evaluated for SHG response by a modified
Kurtz–Perry powder method and the results are shown in
Table 2. For compounds 1–3 the measured SHG values are 8.8,
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2 (a) B. K. Saha, A. Nangia and J.-F. Nicoud, Cryst. Growth
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46.4, 46.3, 36.7, 26.3, 25.0, 23.2, 23.1, 21.2 ppm; HRMS
calculated for C18H23N2O3 (M
315.1508.
+
H)+: 315.1703 found:
+
2-(1-Oxo-3-phenyl-1-(pyrrolidin-1-yl)propan-2-yl)isoindoline-
1,3-dione (2). Yield = 83%; Melting point 145 uC (DSC); [a]D18:2
2136.9; FTIR (KBr) nmax (cm21) 3062, 3029, 2936, 2867, 1718,
1646, 1467, 1432, 1381, 1331, 1167, 1099, 723, 497; 1H NMR
(400 MHz, CDCl3): d 7.76 (2H, m), 7.67 (2H, m), 7.18 (5H, m),
5.13 (1H, dd, J = 9.56, 6.6 Hz), 3.58 (4H, m), 1.82 (4H, m) ppm;
13C NMR (100 MHz, CDCl3): d 167.6, 166.6, 137.1, 134.0, 131.3,
129.1, 128.4, 126.6, 123.3, 54.3, 46.5, 46.0, 34.7, 26.2, 23.7 ppm;
HRMS calculated for C21H21N2O3 (M + H)+: 349.1547 found:
+
349.1266.
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2-(1-Oxo-3-phenyl-1-(piperidin-1-yl)propan-2-yl)isoindoline-
1,3-dione (3). Yield = 80%; Melting point 150 uC (DSC); [a]D19:4
2174.5; FTIR (KBr) nmax (cm21) 3030, 2934, 2922, 2858, 1718,
1645, 1453, 1440, 1381, 1080, 717, 528, 489; 1H NMR (400 MHz,
CDCl3): d 7.75 (2H, m), 7.67 (2H, m), 7.18 (5H, m), 5.30 (1H,
dd, J = 10.24, 5.88 Hz), 3.7 (1H, dd, J = 14.3, 11.0 Hz), 3.60 (2H,
m), 3.43 (1H, dd, J = 14.64, 5.16 Hz), 3.32 (m, 2H), 1.57 (2H, m),
1.53 (4H, m) ppm; 13C NMR (100 MHz, CDCl3): d 167.7, 166.5,
137.2, 134.0, 131.4, 129.0, 128.4, 126.7, 123.3, 52.7, 46.6, 43.6,
+
35.0, 26.2, 25.4, 24.3 ppm; HRMS calculated for C22H23N2O3
(M + H)+: 363.1703 found: 363.1400.
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Acknowledgements
BR is grateful to the Department of Science and Technology,
Ministry of Science and Technology, India for financial
support (SR/FT/CS-108/2010).
Notes and references
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