Synthesis, characterization, and third-order nonlinear optical properties of a new neolignane analogue

Article abstract of DOI:10.1039/c6ra14961h

Recently, a wide number of pharmacological activities, such as anti-leishmanial, antioxidant and antitumor, have been discovered for neolignane analogues. To provide a view of the non-linear optical behavior of the third order of the crystal 2-(4-nitrophe

Full text of DOI:10.1039/c6ra14961h

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Synthesis, characterization, and third-order
nonlinear optical properties of a new neolignane
Cite this: RSC Adv., 2016, 6, 79215
analogue†
ab
b
c
b
Wesley F. Vaz, Jean M. F. Custodio, Rafael G. Silveira, Adailton N. Castro,
d
e
e
Carlos E. M. Campos, Murilo M. Anjos, Guilherme R. Oliveira,
Clodoaldo Valverde, Basılio Baseia and Hamilton B. Napolitano*
bfg
hi
b
´
Recently, a wide number of pharmacological activities, such as anti-leishmanial, antioxidant and antitumor,
have been discovered for neolignane analogues. To provide a view of the non-linear optical behavior of the
third order of the crystal 2-(4-nitrophenoxy)-1-phenylethanone (NPH-PE) in the static and dynamic cases,
we calculated its linear polarizability (a) and second hyperpolarizability (g). We used a new supermolecule
approach combined with an iterative electrostatic system whose atoms of the neighboring molecules are
represented by point charges. A comprehensive investigation of NPH-PE is reported by single crystal X-ray
diffraction and FT-Raman and NMR spectroscopy. In addition, a combination of density functional theory
Received 8th June 2016
Accepted 29th July 2016
(DFT) with the CAM-B3LYP functional and the 6-311+G(d) basis set was used to calculate the molecular
structure optimization, the vibrational frequencies, and the intensity of the vibrational bands. Concerning
the values of the third-order optical nonlinearity, the second hyperpolarizability of the embedded
molecule showed an increase of 125 058% in comparison with the corresponding result in the static case.
DOI: 10.1039/c6ra14961h
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of the fact that this wide range of compounds exhibits biological
potential such as anti-leishmanial, antioxidant, and antitumor
1
. Introduction
1
3–5
6
The term “lignans” was rst introduced by Haworth and was activities
assigned to plant products derived from carbon skeletons in mycobacterial properties. Recently, Hanusch et al. described
as well as anti-schistosomiasis and anti-
7
8
0
which the propenylbenzene units (C3–C6) 8.8 are linked by the genotoxicity and evaluated the cytotoxicity of the neolignan
carbons (b –b). However, due to increased understanding of analogue 2-(4-nitrophenoxy)-1-phenylethanone. In order to
0
various structures, this assignment become obsolete; lignoids better understand the results found by Hanusch, more detailed
now are subdivided into more groups, such as (a) lignans; (b) structural study of the analyzed compound is required. Among
neolignans; (c) alolignanas; (d) norlignanas; (e) oligolign ´o ides; the available techniques and methodologies for this purpose,
2
and (f) heterolign ´o ides. The structural study of neolignans has an important role is played by crystallographic analysis because
attracted attention in the scientic community recently, in view it evaluates the composition and chemical structure of the
9
compound. Moreover, the knowledge of the crystalline struc-
ture of an organic sample enables the calculation of its various
Instituto Federal de Educaç a˜ o, Ci ˆe ncia e Tecnologia de Mato Grosso, 78455-000, electrical properties.
a
Lucas do Rio Verde, MT, Brazil
The fascination with new organic materials for nonlinear
optical (NLO) applications has widely stimulated their study in
the past 30 years; this interesting topic has been considered by
b
Ci ˆe ncias Exatas e Tecnol ´o gicas, Universidade Estadual de Goi a´ s, 459, 75001-970,
An a´ polis, GO, Brazil. E-mail: hamilton@ueg.br
c
Departamento de Qu ´ı mica, Universidade Federal de S a˜ o Carlos, CEP: 13565-905, S a˜ o
10
many researchers, such as Champagne and Bishop. Organic
molecules, especially polymers with high hyperpolarizability,
have raised great interest due to their applications in nonlinear
Carlos, SP, Brazil
d
Departamento de F ´ı sica, Universidade Federal de Santa Catarina, 88040-970,
Florianopolis, SC, Brazil
´
11
e
Instituto de Qu ´ı mica, Universidade Federal de Goi a´ s, Goi aˆ nia, GO, Brazil
Escola Superior Associada de Goi aˆ nia (ESUP), 74840-090, Goi aˆ nia, GO, Brazil
optical systems. Their relative ease of synthesis and manipula-
tion and their more efficient NLO have placed organic structures
at the border of research and technological applications that have
elicited much attention; even today, several studies have been
published related to chromophore synthesis in order to optimize
f
g
Universidade Paulista (UNIP), 74845-090, Goi aˆ nia, GO, Brazil
h
Instituto de F ´ı sica, Universidade Federal de Goi a´ s, 74.690-900, Goi aˆ nia, GO, Brazil
i
Departamento de F ´ı sica, Universidade Federal da Para ´ı ba, 58.051-970, Jo a˜ o Pessoa,
PB, Brazil
12,13
the non-linear optical properties of crystalline materials.
†
Electronic supplementary information (ESI) available. CCDC 1481520. For ESI
and crystallographic data in CIF or other electronic format see DOI:
0.1039/c6ra14961h
Theoretical research has played an invaluable role in
increasing our understanding of experimental data, such as the
1
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˚
microscopic origin of molecular responses in NLO. The super- (l ¼ 0.71073 A). The structure was solved by direct methods and
2
molecule approach, using this method in an iterative process, rened by full-matrix least squares on F using SHELXL2014
27
can simulate the effect of the polarization of a medium on the soware. The studied compound crystallized in the mono-
28
electrical properties of organic molecules. This polarization clinic crystal system and space group P2 /c, with the following
1
˚
˚
˚
procedure relies on the fact that the dominant intermolecular unit cell metrics: a ¼ 8.093(5) A, b ¼ 13.179(7) A, c ¼ 11.412(6) A,
ꢀ
ꢀ
interactions are electrostatic in nature and takes long-range g ¼ a ¼ 90 and b ¼ 91.431 (19) . The main crystallographic
electrostatic effects into account; therefore, we can estimate data are shown in Table 1. All the hydrogen atoms were placed
the dipole moment, the linear polarizability and the second in calculated positions and rened with xed individual
hyperpolarizability of a crystal surrounded by a polarizable displacement parameters [Uiso(H) ¼ 1.2 Ueq or 1.5 Ueq] accord-
ꢀ
ꢀ
domain constituted by other atoms of neighboring molecules, ing to the riding model (C–H bond lengths of 0.97 A and 0.96 A
14–17
treated as point charges.
The incorporation of polarization for aromatic and methyl groups, respectively). Molecular
effects in the material medium modies the action of inter- representations, tables and pictures were generated by the
18
29
molecular interactions on the electrical properties. Reliable Mercury and Crystal Explorer v3.1 (ref. 30) programs. The
relationships of structural properties are required in the design possible interactions of hydrogen were checked by PARST
31
of optical materials for effective applications in photonic soware and studied from the Hirshfeld surface. The crystal-
devices, such as optical modulators, electro-optics, and other lographic information les of the C14 molecule were
optical equipment. deposited in the Cambridge Structural Database under the
H
11NO
4
32
The aim of this study is to determine the third order optical code CCDC 1481520.
nonlinearities of the compound 2-(4-nitrophenoxy)-1-
phenylethanone (NPH-PE). To this end, we present an ab ini-
tio study using the procedure of supermolecule polarization to
Hirshfeld surface analysis
calculate the linear polarizability (a) and second hyper- The potential intermolecular interactions of NPH-PE were
polarizability (g) in the static and dynamic cases. Recently, it visualized and interpreted using Hirshfeld surface analysis.
was proposed that an unconventional blockade may allow This is a graphical tool for the visualization and understanding
emission of light to reach antibunched passive devices made of of intermolecular interactions. The Hirshfeld surface arose
3
19,20
materials with high susceptibility c , such as silicon.
In from an attempt to dene the space occupied by a molecule in
21
another recent work, the authors developed the same tech- a crystal in order to partition the crystal electron density into
nique of polarization used here to estimate the non-linear molecular fragments. A share in the charge density can be
optical properties c and c of molecular crystals, with made at each point between the atoms, in relation to the free-
33
1
2
reasonable results compared with those of experiments. Other atom densities at the corresponding distances from the
1
schemes of embedding general/local eld theory to calculate c
and c were also developed for molecular crystals.
nuclei. This entails the generation of well-localized bonded
2
22–26
In this atom distributions, each of which closely resembles the
paper, we calculate the NLO properties for the static and molecular density in its neighborhood. The integration of the
dynamic cases. We also calculate the energy of the HOMO and atomic deformation densities determines the net atomic
LUMO through the MP2 method.
charges and multipole moments, leading to molecular charge
reorganization. This allows us to calculate the external electro-
static potential and the interaction energy between molecules or
2. Experimental and computational
procedures
Synthesis and crystallization
Table 1 Crystal data and structure refinement for NPH-PE
To a suspension of K CO (5 mmol) and 4-nitrophenol (1 mmol)
in dry butanone (30 mL) at 50 C was added a solution of phe- Temperature
nacyl bromide (1.5 mmol/10 mL of butanone). The resulting Wavelength
2
3
Formula weight
257.24 a.u.
293(2) K
0.71073 A
ꢀ
100(2) K
1.77142 A
˚
˚
Crystal system, space group, Z
Unit cell dimensions
1
Monoclinic, P2 /c, 4
mixture was stirred until the starting material was consumed
observed by TLC) and water (20 mL) was added; the product
˚
7.829(1) A˚
a ¼ 8.0930(5) A
(
˚
˚
b ¼ 13.1790(7) A
13.160(3) A
was then extracted with ethyl acetate (30 mL ꢁ 3). The organic
˚
˚
c ¼ 11.4120(6) A
11.399(3) A
ꢀ
ꢀ
layers were combined, washed with water, HCl 10%, and brine,
a ¼ 90
90
ꢀ
ꢀ
b ¼ 91.43(2)
92.29(1)
90
2 4
and dried over anhydrous Na SO . The solvent was removed
ꢀ
ꢀ
g ¼ 90
under reduced pressure and the product was recrystallized with
a hexane–acetate mixture to obtain a light yellow solid in 80%
yield.
3
˚
3
˚
Volume
1216.80(12) A
1173.61 A
1.452 mg m
1.552 mm
ꢂ3
ꢂ3
ꢂ1
Calculated density
Absorption coefficient
F(000)
1.404 mg m
ꢂ1
0.104 mm
536.00
Reections collected/unique
Renement method2
6420/2258 [R(int) ¼ 0.293]
Crystallographic characterization
Direct method
1.028
Rietveld
The X-ray diffraction data of the analyzed compound were Goodness-of-t on F
collected at room temperature using a Bruker APEX II CCD
3.05
Final R indices [I > 2s(I)]
0.0392
0.03181
diffractometer with graphite-monochromated MoKa radiation
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a Peltier-cooled charge-coupled device CCD detector, allowing
ꢂ1
us to obtain a spectral resolution of 6 cm . All spectra were
ꢂ1
recorded in the spectral window of 200 to 1800 cm with the
same acquisition time (10 s).
NMR spectroscopy characterization
All NMR experiments were performed on a BRUKER DRX 400
MHz spectrometer with a BBO 5 mm probe at 298 K (all signals
are reported in ppm with TMS (tetramethylsilane) as the
1
13
internal reference). H, C, DEPT-135 NMR and advanced 2D
1
1
NMR techniques such as gradient enhanced, H– H COSY, and
1
13
3
H– C correlation HSQC were employed, using CDCl as the
solvent. The splitting of proton and carbon resonances were
1
reported as s ¼ singlet, tt ¼ triple triplet and m ¼ multiplet. H
NMR (400.21 MHz, CDCl , 298 K) d (ppm) 6.97–7.03 (m, 2H);
3
8
2
.17–8.24 (m, 2H); 5.44 (s, 2H); 7.97–8.03 (m, 2H); 7.51–7.58 (m,
3
4
13
H); 7.67 (tt, Jortho ¼ 7.6 Hz and Jmeta ¼ 1.6 Hz, 1H). C NMR
(400.21 MHz, CDCl
3
, 298 K): d (ppm) 162.9 (C4); 114.81(C3, C5);
1
1
25.91 (C2, C6); 142.12 (C1); 70.00 (C7); 192.82 (C8); 134.03 (C9);
29.08 (C14, C10); 128.00 (C11, C13); 134.38 (C12).
Infrared spectroscopy and assignments
Fig.
1
(a) Synthesis of 2-(4-nitrophenoxy)-1-phenylethanone; (b) The experimental absorption spectrum in the solid state was
ꢂ1
experimental (red), theoretical (black) and overlap of the IR and Raman observed in the region from 4000 to 400 cm using an FT-IR/
spectra of NPH-PE.
IRAffinity-1 Shimadzu spectrophotometer. The sample was
screened in potassium bromide (KBr) and the main absorbent
groups were characterized. The synthesis and the experimental
3
4
between parts of the same molecule. Thus, interactions found
in NPH-PE were mapped as a function of d (the distance from
4
infrared and Raman spectra of C14H11NO are shown in Fig. 1.
ꢀ
ꢀ
e
The obtained solid was colorless, mp: 147 C to 148 C. The
starting geometry used in the calculations was taken directly
from the X-ray data and was fully optimized without constraint
using density functional theory (DFT) as implemented in the
the surface to the nearest atom in the molecule itself) and d (the
distance from the surface to the nearest atom in another
molecule) by Crystal Explorer 3.1 (ref. 30) soware, with
ngerprint plots using the standard 0.6–2.8 A view of d
i
˚
38

e
vs. d
i
.
Gaussian 09 package of programs. Handy and co-workers' long
range corrected version of B3LYP using the Coulomb-
39
attenuating method, CAM-B3LYP, was employed throughout
the calculations. This functional is a hybrid with improved long-
range properties and is recommended as highly accurate for the
polarizability of long chains, excitations to Rydberg states and
charge transfer excitations. The extended Gaussian basis set 6-
Powder diffraction
XRPD patterns of 2-(4-nitrophenoxy)-1-phenylethanone,
C H NO , were recorded at room temperature on a XPERT
1
4
11
4
PANalytical diffractometer equipped with an X'Celerator
detector using ltered Ka radiation from a Cu tube operating at
0 kV and 45 mA. Further measurements were performed at the
1
40,41
311+G(d) of Pople and co-workers
was used for all the
4
computations. To conrm that the fully optimized geometry
was found in a local minimum, analytic harmonic frequency
calculations were carried out at the same level of theory. The
absence of imaginary frequencies shows that the optimized
structure is truly in a local minimum. The assignments of the
vibrational frequencies were carried out by potential energy
XRD1 beamline of Brazilian Synchrotron, using 7 and 12 keV
photons at room temperature and 100 K. All the measurements
were carried out in transmission mode using a 0.7 mm glass
capillary. The procedures for the structural determination were
3
5
carried out using DASH, and the molecular structure was given
by RNM. Rietveld analyses of the patterns were performed using
42
distribution (PED) analysis using VEDA 4 soware and were
36,37
GSASEXPGUI
and TOPAS version 4.2 (Bruker AXS GmbH,
43
supported by the animation option of Gaussview.
Karlsruhe, Germany).
Computational procedures
Raman spectroscopy
Molecules can be characterized by their electrical properties,
Raman spectra of different regions of the sample surface were such as dipole moment (m), linear polarizability (a), rst
collected with a 20ꢁ objective lens at room temperature using hyperpolarizability (b), and second hyperpolarizability (g). The
a PeakSeeker 785 (RAM – PRO – 785) Raman system with a diode essential requirement is that molecular (b) organic materials
laser of 785 nm and 50 mW at the source. The backscattered exhibit no inversion center, i.e., they must be non-
11
Raman radiation was dispersed with a grating and focused on centrosymmetric
materials.
As
NPH-PE
exhibits
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a centrosymmetric crystal structure, its rst hyperpolarizability (ii) and repeated the procedure until convergence in the electric
is null. Here, a supermolecule approach was developed to detect molecular properties was achieved. In each iterative process, we
the polarization effects of the crystalline environment upon the calculated the linear and nonlinear electrical properties for
electrical properties of NPH-PE. This method was used in the both the static and dynamic cases via the MP2 and Density
experimental geometry of the asymmetric unit of NPH-PE, Functional Theory (CAM-B3LYP) levels, using the 6-311+G(d)
including 30 atoms. Initially, we took the unit cell of the NPH- basis set employing the nite eld (FF) method. These calcu-
PE molecule, consisting of four asymmetric units; by repli- lations show that a set of 5 ꢁ 5 ꢁ 5 unit cells guarantees fast
cating it in all three axes, the settings 3 ꢁ 3 ꢁ 3 (27 unit cells convergence of the dipole moment of the crystal; therefore, we
with 3240 atoms), 5 ꢁ 5 ꢁ 5 (125 unit cells, with 15 000 atoms), used a larger arrangement (9 ꢁ 9 ꢁ 9) to ensure a stable dipole
7
ꢁ 7 ꢁ 7 (343 unit cells with 41 160 atoms) and the 9 ꢁ 9 ꢁ 9 moment. All calculations were performed using the Gaussian 09
conguration (729 unit cells with 87 480 atoms) were obtained. program. In this study, the values of average linear polarizability
Each atomic conguration around the isolated NPH-PE mole- hai, the total dipole moment m and the second average hyper-
cule is treated as a point charge. To this end, we initiated it (step polarizability hgi have been calculated through the following
0
) with the isolated molecule via a t of the electrostatic expressions, respectively:
potential (ChelpG) obtained with the 6-311+G(d) basis set at the
MP2 level, described by its charge distribution in a vacuum; (i)
we then calculated the partial atomic charges (ChelpG) for one
isolated molecule of the asymmetric unit; (ii) in the position of
each corresponding atom in the generated unit cells, we
replaced the atom by its partial atomic charge, calculated in
item (i); (iii) we calculated the static electric properties (dipole
moment and second hyperpolarizability) and the new partial
atomic charges of the asymmetric unit; (iv) we returned to item
1
3
ꢀ
ꢁ
hai¼
a
xx þ ayy þ azz
;
(1)
(2)
(3)
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
2
2
m ¼
m
þ m þ m ;
x
y
z
X ꢀ
ꢁ
1
hgi ¼ 1
giijj þ gijij þ gijji
:
5
ij¼x;y;z
Fig. 2 (a) ORTEP diagram of ellipsoids at the 30% probability level with the atomic numbering scheme for NPH-PE. All bonds are in the normal
range, and hydrogen atoms are shown as spheres of arbitrary radii. View normal to (100). (b) The crystal packing of NPH-PE, stabilized by
nonclassical hydrogen bonds, including C10–H10/O4; C6–H6/O4; C6–H6/O3 [symmetry code: ꢂx + 1, +y ꢂ 1/2, ꢂz ꢂ 1/2]; C13–H13/O1
[
symmetry code: ꢂx, ꢂy + 1, ꢂz]. Interactions are drawn as dashed lines.
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We used Kleinmann symmetry; therefore, only the hgi in the Table 2 The calculated and experimental geometric parameters for
NPH-PE
static case is reduced to
1
ꢀ
ꢀ
ꢁꢁ
Bond distance
(A)
hgi ¼ 5 gxxxx þ gyyyy þ gzzzz þ 2 g
þ gxxzz þ gyyzz
:
(4)
xxyy
˚
ꢀ
X-ray
DFT
Bond angle ( ) X-ray
DFT
C14–C13
1.3699 1.3842 C09–C14–C13
1.3704 1.3902 C14–C13–C12
1.3802 1.3880 C13–C12–C11
1.3840 1.3873 C12–C11–C10
1.3836 1.3948 C11–C10–C09
1.3923 1.3947 C10–C09–C14
1.4812 1.4944 C09–C08–O01
1.2045 1.2034 C09–C08–C07
1.5041 1.5246 O01–C08–C07
1.4182 1.4019 C08–C07–O02
1.3618 1.3491 C07–O02–C01
1.3873 1.3943 O02–C01–C02
1.3855 1.3868 O02–C01–C06
1.3764 1.3814 C01–C02–C03
1.4542 1.4648 C02–C03–C04
1.2274 1.2169 C03–C04–C05
1.2271 1.2175 C04–C05–C06
1.3821 1.3907 C05–C06–C01
1.3733 1.3763 C06–C01–C02
1.3900 1.3984 C05–C04–N01
C04–N01–O03
120.80 120.38
119.73 120.01
120.61 120.04
119.91 119.97
119.80 120.32
119.28 119.27
120.60 121.97
119.07 117.09
120.33 120.94
107.77 108.78
118.61 119.17
114.70 115.29
124.74 124.58
120.04 120.21
118.98 119.07
121.74 121.49
119.40 119.50
119.27 119.61
120.56 120.12
119.36 119.18
118.67 117.72
123.40 122.91
118.81 117.81
122.52 124.46
118.90 119.32
117.30 117.82
1
Next, to estimate the linear macroscopic parameter c of the C13–C12
crystals, we can use the following relationship:
C12–C11
C11–C10
a
ij
ð1Þ
C10–C09
C14–C09
C09–C08
C08–O01
C08–C07
c
¼ 3
;
(5)
ij
0
V
where the components aij (i, j standing for x, y, z) of the linear
polarizability are given in Table 5, 3
) is the vacuum permittivity, and V is the volume of the unit C07–O02
cell (see Table 1). The experimental quantity, the third-order C01–O02
electric susceptibility c , is related to the second hyper-
polarizability by the expression
ꢂ12
0
(8.85418782 ꢁ 10
F
ꢂ1
m
3
C06–C01
C06–C05
C05–C04
C04–N01
N01–O03
N01–O04
C04–C03
C03–C02
C02–C01
N
ð3Þ
c
¼ V hgi;
(6)
with N standing for the number of atoms in the unit cell.
3
. Results and discussion
Crystallographic structure
C08–C09–C10
C04–N01–O04
O04–N01–O03
C03–C04–N01
The neolignane analogue NPH-PE belongs to the class of
compounds constituted by ketones containing a keto group
bound to a six-membered substituted aromatic ring. The C7–O2
bond shows a lower free capacity of rotation when compared
with other heteroatoms, such as sulfur, even considering the
size of the atom and its electronegativity. Consequently,
different biological activities are observed between sulfurated
C08–C09–C14
The crystalline arrangement of the analyzed compound is
stabilized by three non-classical hydrogen bonds, as shown in
Table 3. The linear periodicity along the b axis is sustained by
C10–H10/O4 [D/A ¼ 3.498 A˚ , D–H/A ¼ 165.09 and
ꢀ
44
and oxygenated analogues. NPH-PE crystallizes in the mono-
clinic centrosymmetric space group P2 /c, with cell parameters
symmetry code: ꢂx + 1, +y ꢂ 1/2, ꢂz ꢂ 1/2], C6–H6/O4 [D/A ¼
1
ꢀ
˚
˚
˚
ꢀ
3.572 A, D–H/A ¼ 164.56 and symmetry code: ꢂx + 1, +y ꢂ 1/2,
ꢂz ꢂ 1/2] and C6–H6/O3 [D/A ¼ 3.432 A˚ , D–H/A ¼ 135.30
˚
a ¼ 8.093(5) A; b ¼ 13.179(7) A; c ¼ 11.412(6) A; a ¼ 90 , b ¼
3
ꢀ
ꢀ
ꢀ
˚
9
0
1.431(19) and g ¼ 90 ; V ¼ 1216.80(12) A ; nal indices R
1
¼
and symmetry code: –x + 1, +y ꢂ 1/2, ꢂz ꢂ 1/2] non-classical
.0392; and goodness-of-t (S) ¼ 1.028, showing four molecules
interactions. The portions formed by the aforementioned
in the asymmetric unit. The data for the nal structural
renements are shown in Table 1. The ellipsoid displacement
plot of the asymmetric unit (with labeling) and the crystal
packing of NPH-PE are presented in Fig. 2. The X-ray geometry
parameters (bond lengths and bond angles) were compared
with fully optimized geometric parameters; the results were very
similar.
˚
interactions are related by C13–H13/O1 [D/A ¼ 3.162 A,
ꢀ
D–H/A ¼ 148.54 and symmetry code: ꢂx, ꢂy + 1, ꢂz] inter-
actions, forming the two-dimensional arrangement shown in
Fig. 2(b).
In addition to stabilizing the crystalline arrangement, the
non-classical interactions already discussed contribute to the
formation of an empty space between the molecules of the layer
depicted in Fig. 2(b), similar to a micelle. This can be conrmed
by Fig. 3, which shows the interaction maps of the part of the
The roots of the mean squared errors (RMSE) for internu-
clear distances and bond angles were calculated in this work.
On average, the correlation between the experimental and
˚
theoretical values is very good, with RMSEs of 0.0024 A for the
ꢀ
distances and 15.5 for the angles. Large discrepancies between
a
Table 3 Non-classical hydrogen bonds of NPH-PE
the theoretical and the experimental bond distances and angles
were not observed. In general, large deviations between these
measures exist because the X-ray results are in the solid phase,
while the geometry was optimized for the free molecule in C13–H13/O1
a vacuum. An angle of 3.71 between the planes of the aromatic C10–H10/O4
rings in the packing conrms the planarity of the structure. The
optimized and experimental geometry parameters are pre-
sented in Table 2.
ꢀ
D–H/A
d(D–H)
d(H/A)
d(D/A)
d(D–H/A) ( )
(
i)
0.993
0.954
0.927
0.927
2.272
2.568
2.670
2.711
3.162
3.498
3.572
3.432
148.54
165.09
164.56
135.3
ꢀ
(ii)
(
(
ii)
ii)
C6–H6/O4
C6–H6/O3
a
Symmetry codes: (i) ꢂx, ꢂy + 1, ꢂz; (ii) ꢂx + 1, +y ꢂ 1/2, ꢂz ꢂ 1/2.
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Fig. 5 The Hirshfeld surface dnorm map of NPH-PE for visualizing
intercontacts, showing the layer stabilized by non-classical hydrogen
bonds, including C10–H10/O4; C6–H6/O4; C6–H6/O3
[
symmetry code: ꢂx + 1, +y ꢂ 1/2, ꢂz ꢂ 1/2]; C13–H13/O1 [symmetry
code: ꢂx, ꢂy + 1, ꢂz]. The interactions are drawn as dashed lines.
Fig. 3 Interaction maps and hotspots for the NPH-PE arrangement.
The regions of H-bond donors, H-bond acceptors and hydrophobic
groups are represented by blue, red and green. The first contour is
represented by an initial level of 2,0 and opacity 0,2, the second
contour level is 4,0 with opacity 0,5 and the third contour has an initial
level of 6,0 and opacity 0,8.
nitro group) and Cg2 (the aromatic ring closest to the carbonyl
group). Fig. 4(a) shows the rst p-stacking interaction, Cg1/
˚
Cg2(i), with a distance of 3.961 A, and the second p-stacking
˚
interaction, Cg1/Cg2(ii), with a distance of 4.296 A, alternating
to form the three-dimensional arrangement of NPH-PE
layer formed by four molecules. This picture shows the regions
of the H-bond donors, H-bond acceptors and hydrophobic
groups, represented by blue, red and green colors, respectively.
Each interaction is described by three map contour levels, being
the rst, second and third contours with the initial levels of 2,0,
[
symmetry codes: (i) ¼ (ii) ¼ 1 ꢂ x, ꢂy, 1 ꢂ z].
Hirshfeld surface analysis is an excellent tool for qualitative
analysis of the intermolecular contacts of crystal packing. As an
additional methodology, this analysis highlights the areas of
non-classical hydrogen bonds and p–p interactions. Fig. 5
4,0 and 6,0, respectively. We can note the absence of interac-
45
shows the Hirshfeld surface dnorm of NPH-PE, where the layer
is stabilized by bifurcated non-classical interactions involving
the C6, H6, O3 and O4 atoms (b) and C10–H10/O4 non-
classical interactions around the H-bond donor regions and
C13–H13/O1 around the H-bond acceptor regions. Red indi-
cates the region of highest interaction, and white and blue
tions in the empty space.
There are no non-classical hydrogen bonds responsible for
the crystal packing represented in Fig. 2(b). This stability is
achieved by p-stacking (or p–p) interactions. The layers are
connected via the centroids Cg1 (the aromatic ring closest to the
Fig. 4 (a) Representation of p–p interactions by dotted lines, establishing the crystal packing of NPH-PE. Cg1 and Cg2 represent the centroids of
the aromatic rings, respectively; (b) Hirshfeld surface shape index showing the complementary patches where p–p interactions occur, indicated
by arrows. [Cg1/Cg2 ¼ (i) 3.961 A˚ ; (ii) 4.296 A˚ .]
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Fig. 6 Fingerprint of NPH-PE. (a) Total interactions, (b) H/H, (c) O/H, (d) C/H, (e) C/O, (f) C/C. The outline of the full fingerprint is shown in
gray. d is the closest internal distance from a given point on the Hirshfeld surface, and de is the closest external contact.
i
indicate regions of weaker interactions. As an intermolecular and correspond to hydrogen-bond donors; the lower spikes
45
contact tool, Hirshfeld surface analysis plays an important role indicate hydrogen-bond acceptors (d
i e
> d ). Hydrophobic
in the description of p–p interactions. Such interactions are interactions (C/C, C/H and H/H contacts) can also be
46
quantitatively described by PLATON soware and qualitatively observed in Fig. 6. The signicant overlap of molecules of NPH-
˚
described by the Hirshfeld surface shape index, as can be seen PE results in greater contact in d
e
¼ d
i
¼ 1.8 A. It is represented
in Fig. 4(b). The Hirshfeld surface shape index can be used to by the green region in images 6(a) and (f). X-ray powder patterns
identify additional empty (red) and lled (blue) regions where of NPH-PE samples were collected at three different wave-
two molecules meet. Note the two triangular shapes above the lengths and two different temperatures. Structural renement
Cg1 and Cg2 centroids in Fig. 4(b). The rst red triangle, using the Rietveld method supports the NPH-PE crystallo-
combined with the second blue triangle, forms a “bowtie” graphic structure, also in powder form [Fig. 7(a)].
shape, indicating the presence of p–p interactions.
XRPD measurements were performed to verify the packing
Finally, in addition to indicating classical, non-classical and and molecular conformation of NPH-PE in powder form.
p–p interactions, Hirshfeld surface analysis also provides Although Fig. 7(a) shows good visual agreement between the
a unique identication for each molecule, called a ngerprint. calculated pattern (obtained using CIF from single crystal
Fingerprints are the combination of d contacts (ordinate – analysis) and the experimental patterns, Rietveld analysis gave
e
distance from the surface to the nearest atom exterior to the no satisfactory tting or records for the NPH-PE compound [see
surface) against d contacts (abscissa – distance from the surface Table 1 and Fig. 7(b)]. Next, many attempts to nd a better
i
to the nearest atom interior to the surface) in a two-dimensional structural solution using DASH and the molecular structure
graph in order to represent the percentage contribution of each given by RNM were carried out, but with no success. As pref-
47
type of interaction present in the molecule. The hydrogen erential orientation is not expected using capillaries as sample
bonds (O/H contacts) are responsible for the ngerprints of holders, this mist of the pattern built with CIF and experi-
graphics; they are also recognized as a pair of sharp spikes, as mental patterns suggests a polymorphic susceptibility of the
shown in Fig. 6. The upper spikes are in regions where d
e
> d
i
NPH-PE compound [Fig. 7(b) and (c)].
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Table 4 MP2/6-311+G(d) results for the components of the dipole
moment (in D) as a function of the number of iterative processes
0
1
2
3
4
5
6
7
m
m
m
m
x
y
z
ꢂ0.82 ꢂ0.79 ꢂ0.85 ꢂ0.85 ꢂ0.85 ꢂ0.85 ꢂ0.85 ꢂ0.85
ꢂ7.37 ꢂ8.68 ꢂ8.98 ꢂ9.06 ꢂ9.08 ꢂ9.08 ꢂ9.08 ꢂ9.09
0.32
7.42
0.21
8.72
0.16
9.00
0.14
9.07
0.13
9.10
0.13
9.10
0.13
9.10
0.13
9.10
ꢂ24
Table 5 MP2/6-311+G(d) results for the linear polarizability (in 10
esu) as a function of the number of iterations
0
1
2
3
4
5
6
7
a
a
a
a
a
a
xx 17.36 17.51
xy 3.87 4.07
yy 35.83 36.32
xz ꢂ6.02 ꢂ6.15
yz ꢂ2.84 ꢂ3.07
zz 23.80 24.02
17.56 17.57 17.58 17.58 17.58 17.58
4.13 4.14 4.15 4.15 4.15 4.15
36.48 36.52 36.53 36.53 36.53 36.53
ꢂ6.20 ꢂ6.21 ꢂ6.22 ꢂ6.22 ꢂ6.22 ꢂ6.22
ꢂ3.16 ꢂ3.17 ꢂ3.18 ꢂ3.18 ꢂ3.18 ꢂ3.18
24.07 24.08 24.09 24.09 24.09 24.09
hai 25.66 ꢂ25.95 26.04 26.06 26.06 26.06 26.06 26.06
We analyzed these results by considering the cases of the
isolated and embedded molecule via MP2: we note that they
converge to 9.10 D, demonstrating that the polarization effect
carries a 22.64% increase to the total dipole moment upon
passing from the isolated molecule to the embedded one. The
m
z
component shows the greatest inuence arising from polar-
ization of the crystalline environment: it shows a decrease of
6.34% compared with the case of the isolated molecule. The
higher contribution to the total dipole moment (m) originates
from the m component.
4
y
The results of the linear polarizability a suffer variations due
to polarization effects of the crystalline environment throughout
the iterative process: we note an increase in the results of all
components of a. The values of the average linear polarizability
ꢂ24
via MP2 converge to 26.06 (in 10
esu), and the ayy component
provides the greater contribution to this result. The results indi-
cate that the polarization effects of the crystalline environment
contribute to a small increase of 1.56% in the average linear
polarizability of the embedded molecule compared with the case
Fig. 7 (a) Overlapping of NPH-PE structure by DRX (black) and DRXP of the isolated molecule – see Table 5. The component azz receives
(
blue); (b) calculated (CIF) and experimental XRPD patterns of NPH-PE
a minor inuence from the polarization of the crystalline envi-
ronment, showing a small increase of 1.22%, whereas the greatest
collected with different excitation energies at room temperature and
low temperature (100 K); (c) experimental (symbols) and theoretical
(
inuence affects the component a , with an increase of 11.97%.
yz
red line) XRPD patterns of NPH-PE with 7 keV at 100 K (the gray line is
The results of the second hyperpolarizability (g) representing
a non-linear response can be seen in Table 6. The results for (g) in
the static case were obtained using CAM-B3LYP/6-311+G(d). The
the difference between both patterns).
Electrical properties
values of the average second hyperpolarizability of the embedded
ꢂ36
molecule converge to 29.39 (in 10
esu), showing that the
The applicability of the supermolecule approach and the elec-
trostatic polarization arrangement are favourable due to the fast
convergence of the iterative process to obtain the dipole moment
and the linear polarizability of the crystal. This calculation was
polarization effect causes an increase of 13.13% in the average
second hyperpolarizability when compared with the case of the
isolated molecule. The highest contribution to the result of g
comes from the component gyyyy. The polarization effect of the

rst performed at the MP2 level using the basic feature base 6-
11+G(d). Table 4 shows the results of this property for NPH-PE,
followed by the respective number of iterations.
crystalline environment has the smallest inuence on the gxxxx
3
component, with an increase of 6.13%; the greatest inuence
comes from the gyyzz component, with an increase of 17.17%.
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Table
polarizability (in 10
number of iterations
6
CAM-B3LYP/6-311+G(d) results for the second hyper-
ꢂ36
esu) in the static case as a function of the
0
1
2
3
4
5
6
7
g
g
g
g
g
g
xxxx 10.77 11.21 11.38 11.42 11.42 11.43 11.43 11.43
yyyy
zzzz
xxyy
xxzz
yyzz
54.72 60.37 61.88 62.20 62.29 62.31 62.32 62.32
11.39 12.16 12.27 12.30 12.31 12.31 12.31 12.31
9.83 10.92 11.19 11.25 11.27 11.27 11.27 11.27
4.23
4.50
4.56
4.57
4.58
4.58
4.58
4.58
12.46 14.03 14.46 14.56 14.59 14.60 14.60 14.60
25.98 28.53 29.19 29.34 29.38 29.39 29.39 29.39
hgi
Fig. 9 LUMO–HOMO of the isolated molecule.
(44.80%)]. In the case of the embedded molecule, the results are
4.39% (14.19%) and [13.20% (55.77%)], as displayed in Table 7.
Fig. 8 stands for the dispersion curves of the isolated and
embedded molecules as a function of the frequency u: in both
cases, it shows similar behaviors of the linear polarizability and
second hyperpolarizability.
For the highest value of the frequency considered, u ¼ 0.10
a.u., the embedded molecule presents the value of second
hyperpolarizability hg(ꢂu; u, 0, 0)i, which is 35.47% larger than
that exhibited by the isolated molecule for the same frequency
(see Fig. 8). Now, when we compare hg(ꢂ2u; u, u, 0)i, this value
becomes 4722.42% smaller. A greater value of the second
hyperpolarizability hg(ꢂ2u; u, u, 0)i was found for the
frequency u ¼ 0.08 a.u.; these values are very signicant
because when comparing them with those of the isolated NPH-
PE molecule in the static case, we found an increase of 2113%,
and when we compared the values of hg(ꢂ2u; u, u, 0)i for u ¼
Fig. 8
polarizability (in 10
Dynamic evolution of the calculated values of the linear
ꢂ24
esu) and second hyperpolarizability (hg(ꢂu; u, 0,
ꢂ36
0
)i in 10
esu) of NPH-PE with respective values of frequencies.
0.08 a.u. with those for the static case, where both are consid-
ered as embedded systems, an increase of 125 058% was
observed. This is a very striking result because in a recent
Relating dynamic second hyperpolarizability
The value hg(ꢂ2u; u, u, 0)i corresponds to a dc-electric eld
induced second-harmonic generation (EFISH), whereas the
value hg(ꢂu; u, 0, 0)i corresponds to the Kerr effect. The
frequency-dependent descriptions of the second hyper-
polarizability are hg(ꢂu; u, 0, 0)i and hg(ꢂ2u; u, u, 0)i for the
isolated and embedded NPH-PE molecules, respectively; the
three frequency standards are u ¼ 0.0239 a.u., u ¼ 0.0428 a.u.,
and u ¼ 0.08 a.u. When comparing the values of the second
hyperpolarizability for the isolated molecule in the static case,
hg(0; 0, 0, 0)i, with the dynamic cases, hg(ꢂu; u, 0, 0)i and
48
experiment by Senthil et al., the authors found a value for the
second hyperpolarizability that was 4400% smaller than the
value found in our case. In the work of Senthil et al., they
employed the stilbazolium crystal, which the authors have
argued could be a possible candidate material for photonic
devices, optical switches, and optical power limiting applica-
tions (Table 7).
Frontier molecular orbitals
The difference in energy of the HOMO and LUMO is an
[
hg(ꢂ2u; u, u, 0)i], for the frequency values a.u. 0.0239 (0.0428
49
important index for the chemical stability of molecules.
A
a.u.), we observe an increase of 3.81% (12.05%) and [11.20%
small HOMO–LUMO gap automatically means small excitation
ꢂ36
Table 7 CAM-B3LYP/6-311+G(d) results of components of the second hyperpolarizability (in 10
esu)
u ¼ 0.08 a.u., l ¼ 569.5 nm
u ¼ 0.0239 a.u., l ¼ 1907 nm u ¼ 0.0428 a.u., l ¼ 1064 nm
ABC
hg(ꢂu; u, 0, 0)i
hg(ꢂ2u; u, u, 0)i
hg(ꢂu; u, 0, 0)i
hg(ꢂ2u; u, u, 0)i
hg(ꢂu; u, 0, 0)i
hg(ꢂ2u; u, u, 0)i
Isolated
Embedded
26.97
30.68
28.89
33.27
29.11
33.56
37.62
45.78
40.36
49.89
574.94
36 748
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ꢂ1
Table 8 Vibrational assignments, experimental and calculated wave numbers in cm of NPH-PE at CAM-B3LYP/6-311+G(d)
Raman
Unscaled Scaled a
Scaled
A
, Raman
infrared
b
Mode no IR freq.
IR freq.
I
FT-IR
Raman freq. scattering activities Raman
IR and Raman assignments
1
2
3
4
5
6
21.58
25.32
45.56
48.04
57.59
111.56
20.67
24.26
43.65
46.02
55.17
106.87
0.37
0.08
3.83
0.99
0.06
0.13
1.72
0.95
4.02
0.61
0.02
0.18
G C
G C
G O
G O
9
C
C
8
C
C
7
O
O
9
C
2
2
8
5
6
1
1
C
C
7
C
4
4
O
3
N
1
+ G C
1
C
6
C
5
C
4
7
2
G C
G C
6
C
C
1
O
2
C
O
7
9
8
C
7
2
+ G C
6
C
1
8
O
2
C
+
G C
G C
G C11
G C
G C
G out C
7 8 9 14
C C C
O
C C C
12 13 14
7
8
9
144.27
158.01
173.39
138.21
151.37
166.11
6.48
3.29
5.06
2.97
0.05
1.04
1
2
C
C
7 8
+ G C
9
C
C
7
O
7
C
8
C
9
C14 + G C
6
C
1
O
2
6
C
7
+
1 2 7 8
O C C
1
1
1
1
1
1
1
1
1
1
2
0
1
2
3
4
5
6
7
8
9
0
187.90
249.83
306.08
326.86
392.54
413.73
432
436.51
453.35
505.84
513.85
180.01
239.34
293.22
313.13
376.05
396.35
413.86
418.18
434.31
484.59
492.27
0.53
4.01
0.00
4.42
1.98
0.01
0.05
0.44
1.70
10.34
2.17
1.81
2.07
1.39
8
C
14
C
C
9
C10 + G C
C
1
O
C
2 7
G C
G C
G C
9
3
1
C
C
C
14
C
13
12
4
6
C
5
C
C
6
+ G O
+ G O
+ G C
3
3
9
C
4
C
4
C
8
O
O
4
4
N
N
1
0.85
0.28
0.00
0.06
0.29
1.72
0.40
1.94
311(w)
C
5
4
1
G N
G C13
G C
G H12
G H
G CHR
G H
+ G H
G H
1
C
4
C
C
3 5
C
7
O
2
14 11 10
C C C
2
C
3
C
5
C
6
C
12
C
11
C10 + G H
7
C
7
O
2
C
1
448(w)
7 7 2 1
C O C
2
+ G C
6 5 7 1
C C N
497(vw)
3
C
3
C
1
C
6
+ r C
7
O
2
C
1
509(vw)
3 3 4 1
C C N
C O C
7 7 2 1
2
1
554.64
531.35
2.31
2.74
534(vw)
5
5
50(vw)
65(vw)
22
23
24
25
26
27
609.47
635.61
639.81
655.24
697.19
700.99
583.87
608.91
612.94
627.72
667.91
671.55
11.79
4.54
2.43
0.56
7.90
37.70
0.35
1.29
6.82
7.39
0.26
6.00
581(vw)
G H14
r C
deformation
G H
u CH R
2
14 13 2
C C C12 + r CH
O C1
8 2
613(w)
630(w)
R
1
6 6 1 2
C C C
2
+ u NO
deformation
deformation + r NO
2
676(w)
R
+
1
R
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
710.66
743.57
782.27
807.76
835.20
874.13
874.84
879.72
907.92
680.81
712.34
749.41
773.83
800.12
837.42
838.10
842.77
869.79
916.97
946.32
967.69
968.45
970.40
988.96
989.68
993.03
1000.73
1022.22
1075.28
1091.12
1097.64
44.29
22.54 750 cm (vs)
0.02
1.91
0.42
0.75
0.05
0.09
0.14
0.11
42.34
0.16
0.27
0.01
4.07
0.07
40.43
0.09
8.79
0.50
19.34
1.25
2.71
33.81
101.17
6.04
u CH R
u C
u CH R
r C
1
1
O
2
C
7
+ u C
+ r CH
4 1 3 2
N O + u NO
42.46
10.04
3.78
39.85
17.55
2.97 846(vs)
61
0.57
2.69
0.03
162.67
0.47
0.93
0.18
2.33
0.59
0.76
5.99
12.37 1070(vs)
42.97
1
2
5
C
7
N
1
u CH R
u CH R
u CH R
2
1
1
+ u CH R
+ u CH R
2
2
847(vw)
876(m)
r NO
r C
G H11
2 8 7 2
+ r C C O
1
C
2
C
6
+ r C
3
C
4
C
5
+ r NO
2
957.17
987.81
C
11
H
10
C10 + r CH
2
t H
t H
5
C
C
5
H
H
6
3
C
C
6
1010.12
1010.91
1012.94
1032.32
1033.07
1036.57
1044.60
1067.04
1122.42
1138.96
1145.76
1150.54
1193.15
2
2
3
975(vw)
999(m)
n CH
u CH R
r C12
r CH
r CH R
t CH R
2
–C]O + r C13
C
14
C
9
1
+ r CH
2
C
11
C
10
2
2
1 2
; r CH
1069(vw)
1107(s)
r C13
r C12
n CH
C
C
14 + r C10
11 + r C11
C
C
11
10 + r C13
C
14
2
–O + r CH R
2
r CH R
2
1102.22 135.18
1143.04
r C C
2 3
+ r C
8
4 2
C10 + n C –NO
1.65
r H12
C12 + H11
C
11
+
r H13
r C
r CH R
C H C
13 14
14
5
5
2
3
1211.91
1218.08
1161.01
1166.92
49.35
15.25
4.36
5.27
6
H
8
C
8
2 3 3
+ r C H C
1168(w)
1
+ r CH R
2
1188(vw)
5
4
1261.92
1208.92 295.85
75.75
1232(m)
9 2
n C C]O + u CH
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Table 8 (Contd.)
Raman
Unscaled Scaled a
Scaled
A
, Raman
infrared
b
Mode no IR freq.
IR freq.
I
FT-IR
Raman freq. scattering activities Raman
IR and Raman assignments
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
1301.62
1320.62
1338.35
1341.25
1366.03
1371.15
1430.14
1439.17
1480.19
1505.28
1508.85
1552.75
1560.27
1630.78
1663.39
1246.95
1265.15 252.41 1234(vs)
0.62
7.50
15.11
9.13
t CH
n asym CH
n asym C R
n O + n asym C R
n asym C R + u CH
r CH R
1331(vs) 1342(vs) n NO
2
1264(m)
2
O
2
C
1
+ n C
3 4
C
1282.14
1284.92
1284.92 164.35
1308.66 31.91
1313.56 390.13 1330(vs)
1378.72
1418.02
1442.06
1445.48
1487.53
65.56
22.95
1
+ r CH R
2
6.27
2
C
1
1
+ r CH R
2
63.66
15.44
458.27
11.85
4.39
3.33
3.00
5.16
9.46
1297(m)
2
2
1
2
32.63
5.27
13.52
46.67 1452(s)
4.95
1380(vw)
1437(vw)
u CH
r CH
n C
r CH
n C
r C
2
2
+ n C
+ n C13
5
C
C
6
+ n C
14 + n C11
2
C
3
8
C
7
C
10
2
1499(vw)
1510(vw)
1582(w)
7
O
2
+ n C10
+ r C C
C
14
C
9
+ C11
12
C C
13
1494.74 136.49
1562.29 191.24 1593(vs)
1593.53
5
C
6
2 3
18.23
6.64
n asym NO
n asym C14
2
10.77
C
9
C
10
+
n asym C11
n asym C
n sym R
n R + n asym NO
C
12
C
13
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
1677.70
1683.93
1693.50
1827.56
3036.91
3079
3193.81
3201.92
3210.91
3220.27
3227.92
3230.36
3234.35
3250.70
3252.67
1607.24 203.80
1613.20 25.30
1622.37 159.52
1750.80 193.98
194.84
123.86
42.65
77.37
80.85
22.10
40.13
117.13
43.60
201.28
58.57
144.67
48.75
59.32
109.40
1594(s)
2 3 4 1 6 5
C C + n asym C C C
1628(vw)
1656(vw)
1695(m)
1
2
2
n C]O
n sym CH
2
n asym CH
2
n CH R
n CH R
n CH R
n CH R
2909.36
2949.68
3059.67
3067.44
3076.05
3085.02
3092.35
3094.68
3098.51
3114.17
3116.06
50.21 2906(vw)
11.82 2929(vw)
1.06
5.34
22.30
10.22
0.69
6.44
7.33
3.46
2.98
1
1
1
1
n H
3
C
3
+ n H
2
C
2
n H13
C13 + n H14C
14
n H
n H
n H
5
6
3
C
C
C
5
6
3
a
b
Scale factor = 0.958. Intensity.
energies to the manifold of excited states. Therefore, so presented in Fig. 1. DFT calculations overestimate the vibra-
50
molecules, with a small gap, will be more polarizable than hard tional frequencies, and a proper scaling factor for CAM-B3LYP
molecules. Fig. 9 represents the distribution of energy levels equal to 0.958 (ref. 51) was used to obtain more coherent values
and the HOMO–LUMO orbitals used at the theory level MP2/6- to compare to the experimental data. The aromatic CH
3
11+G(d) for NPH-PE. As can be seen in Fig. 9, the HOMO stretching vibrations occur at frequencies greater than 3000
ꢂ1
ꢂ1
orbital of the isolated molecule is ꢂ0.3404 eV and that of the cm , in the 3050 to 3010 cm range, while the aromatic CH
ꢂ1
embedded molecule is ꢂ0.3310 eV. The LUMO orbital of the bending occurs at 900 to 690 cm ; these bands can be used to
isolated molecule is 0.0410 eV, whereas that of the embedded assign ring substitution and, nally, the ring stretch absorp-
ꢂ1
ꢂ1 52
molecule is 0.0389 eV. The band gap of the isolated molecule tions occur in pairs at 1600 cm and 1475 cm
energy is 0.3814 eV, whereas that of the embedded molecule is show good agreement with those obtained in this work, as can
.3699 eV. These values indicate that this compound has high be seen by examining Table 8.
. These values
0
chemical stability and high excitation energy.
The methylene group has a characteristic bending absorp-
ꢂ1
tion of approximately 1465 cm
and stretch absorptions
ꢂ1
Infrared, Raman and NMR characterizations
occurring in the 3000 to 2840 cm range; the DFT scaled
frequencies obtained in this work show these absorptions in the
The vibrational, theoretical and experimental frequencies in the
infrared and Raman range show good agreement; therefore, it
was possible to characterize the main absorbing/scattering
groups. The observed discrepancies are justied because the
calculations were made for an isolated molecule in a vacuum,
while the experiments were performed using a solid sample.
Table 8 shows the IR intensities, the calculated vibrational
frequencies for the optimized geometries and the proposed
vibrational assignments. The IR and Raman spectra are
ꢂ1
ꢂ1
ranges of 1246 to 1378 cm and 2909 to 2949 cm , respec-
ꢂ1
ꢂ1
tively, and 1452 cm and 2906 to 2929 cm in the IR spec-
trum, respectively; this is in good agreement with the
characteristics of the methylene group. Aryl ethers give rise to
ꢂ1
two strong bands, an asymmetric C–O–C stretch near 1250 cm
ꢂ1
and a symmetric stretch near 1040 cm ; these bands appear at
ꢂ1
ꢂ1
1
265 cm and 1091 cm in the DFT, respectively, and 1234
ꢂ1
cm and 1070 in the IR, respectively. The band in the 1700 to
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ꢂ1
1
680 cm range in the IR spectrum is assigned as the conju- nonlinearity of the compound NPH-PE. An important result
gation of C]O with the phenyl mode; the calculated value of emerging from this study is the increase of 125 058% in the
ꢂ1
this mode is 1750 cm . The most characteristic bands in the second hyperpolarizability hg(ꢂ2u; u, u, 0)i of the embedded
spectra of nitro compounds are due to the NO2 stretching molecule in comparison with the value obtained for the second
vibrations, which give two strong bands. Conjugation of a nitro hyperpolarizability hg(0; 0, 0, 0)i for the embedded molecule in
group with an aromatic ring presents two bands: 1550 to 1490 the static case. As a future perspective, new insights could be
ꢂ1
ꢂ1
cm (asymmetric) and 1355 to 1315 cm (symmetric). The obtained from investigations of the inuences of different non-
ꢂ1
ꢂ1
bands at 1562 cm and 1313 cm in this paper are assigned to linear crystals in the time evolution of the mentioned proper-
the asymmetric and symmetric modes, respectively. In the IR ties, e.g., when one considers the molecule, via its HOMO–
ꢂ1
ꢂ1
spectra, these bands are at 1593 cm and 1330 cm , respec- LUMO energy levels, behaving as a two level quantum system
tively. The NO scissors occur at higher wavenumbers (850 ꢃ 60 interacting with a single mode of a quantized electromagnetic
2
ꢂ1
53
cm ) when conjugated to C]C or aromatic molecules. The eld; this is an interesting issue that can be explored through
intensity of the NO
equal to 842 cm , and that in the IR spectra is 846 cm . In
54–57
2
scissors band obtained from calculations is the Jaynes–Cummings model, proposed in 1963.
ꢂ1
ꢂ1
aromatic compounds, the wagging mode u NO
2
is assigned at
Acknowledgements
ꢂ1
7
40 ꢃ 50 cm with a moderate to strong intensity. In our DFT
ꢂ1
ꢂ1
scaled frequencies, this band appears at 712 cm and 750 cm
in the IR spectra.
The authors gratefully acknowledge the nancial support of the
National Council of Science and Technology (CNPq), Brazil. The
The structure of NPH-PE can be conrmed by complete authors are also grateful to organizers of the 3rd Edition of the
1
13
assignment of all the H and C signals with the help of School of Crystallization and Crystallography for Latin America
1
13
different 1D ( H, C, DEPT-135) and 2D NMR experiments (ECRISLA-2015) for X-ray single crystal data collection and
1
(
COSY and HSQC). In the H NMR spectrum, 6 signal regions fruitful discussions. XRPD measurements were carried out at
with 11 integrated protons were obtained. Four regions of LDRX-UFSC and at the XRD1 beam line of Brazilian
multiplets at 6.97 to 7.03, 7.51 to 7.58, 7.97 to 8.03, and 8.17 to Synchrotron-LNLS (proposal 20150198).
8.24, all with integrals of 2H, were assigned to H3 and H5, H2
and H6, H14 and H10, and H13 and H11, respectively. The
singlet signal at 5.44 ppm for 2H was assigned to the methylene
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