Theoretical Investigation of Non Linear Optical Properties of Molecules Containing Naphthalene Linked to Nitrophenyl Group MINOR RESEARCH PROJECT [12 th PLAN] MRP-1872/14-15/KLMG016/UGC-SWRO SUBMITTED TO UNIVERSITY GRANTS COMMISSSION PRINCIPAL INVESTIGATOR ANJU LINDA VARGHESE Assistant Professor Department of Chemistry Catholicate College Pathanamthitta, Kerala 1
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Theoretical Investigation of Non Linear Optical Properties of Molecules Containing Naphthalene Linked to Nitrophenyl Group
MINOR RESEARCH PROJECT [12th PLAN]
MRP-1872/14-15/KLMG016/UGC-SWRO
SUBMITTED TO
UNIVERSITY GRANTS COMMISSSION
PRINCIPAL INVESTIGATOR
ANJU LINDA VARGHESE
Assistant Professor Department of Chemistry
Catholicate College Pathanamthitta, Kerala
1
DECLARATION
I hereby declare that the minor research project “Theoretical Investigation of Non Linear
Optical Properties of Molecules Containing Naphthalene Linked to Nitrophenyl Group”is
an original record of studies and research carried out by me during the tenure of the project.
Date: 17 -02- 2017 Principal Investigator
Place: Pathanamthitta
ANJU LINDA VARHGESE
2
Date: 17 February 2017
CERTIFICATE
This is to certify that the Minor Research Project entitled “Theoretical Investigation of Non
Linear Optical Properties of Molecules Containing Naphthalene Linked to Nitrophenyl
Group”MRP-1872/14-15/KLMG016/UGC-SWRO submitted to University Grants Commission
is a bonafidework by ANJU LINDA VARHGESE of our institution.
Principal/Registrar Principal Investigator
3
Contents Page number
Chapter 1: Introduction 1
1.1 Linear Optical Properties 2
1.2 Non Linear Optical Properties 3
1.3 Density Functional Calculations 4
1.4 Basis sets 5
1.5 Objectives 9
Chapter 2: Experimental Section 10
2.1 Computational Details 11
2.2 Chemicals 11
2.3 Synthesis of N-(2,4-dinitrophenyl)naphthalene-1-amine 11
2.4 Characterization Techniques 12
Chapter 3: Results and Discussions 13
3.1 DFT studies on the electronic transitions of N-[3-(Naphthalene-1-yloxy)butyl]-2,4-dinitroaniline, N-[3-(Naphthalene-1-yloxy)butyl]-4-nitroaniline, and their azanaphthalene derivatives
14
3.2 DFT studies on the Non Linear Optical Properties of the above molecule and their structural relationships.
21
4
3.3 DFT studies on the electronic transitions of N-[3-(Quinoline-1-yloxy)butyl]-2,4-dinitroaniline , N-[3-(Quinoline-1-yloxy)butyl]-4-nitroaniline, and their position isomers
28
3.4 DFT studies on the electronic transitions of N-[3-(Quinoline-1-yloxy)butyl]-2,4-dinitroaniline , N-[3-(Quinoline-1-yloxy)butyl]-4-nitroaniline, and their position isomers
34
3.5 DFT studies on the electronic transitions of N-[(Naphthalen-5-yl)methyl]-4 nitrobenzamine and N-[(Naphthalen-5-yl)methyl]-2,4 dinitrobenzamine
36
3.6 DFT studies on the nonlinear optical properties of N-[(Naphthalen-5-yl)methyl]-4 nitrobenzamine and N-[(Naphthalen-5-yl)methyl]-2,4 dinitrobenzamine
38
3.7 DFT studies on the electronic transitions of N-(4-Nitrophenyl)naphthalene-1-amine and N-(2,4-dinitrophenyl)naphthalene-1-amine
39
3.8 DFT studies on the Nonlinear optical properties of N-(4-Nitrophenyl)naphthalene-1-amine and N-(2,4-dinitrophenyl)naphthalene-1-amine
41
3.9 Characterization Techniques 41
3.9.a FT-IR
CHAPTER 4 : Findings &Conclusions 43
4.1 Conclusions 44
4.2 References
ANNEXURE
46
48
5
CHAPTER 1
INTRODUCTION
6
THEORY OF LINEAR AND NONLINEAR OPTICS
Linear and nonlinear optics covers a variety of phenomena involving the interaction of
light with matter. The constantly growing application of optics in technology,
telecommunication, medicine, etc. demanding detailed theoretical modeling, has opened new
fields for theoretical study. Understanding both the linear and nonlinear optical properties of
solids requires a detailed quantum mechanical picture of how electrons move in these materials.
This is an important emerging area of theoretical science.
Most familiar optical processes are proportional to light intensity. But, since the
late1960’s a variety of exciting nonlinear (scaling as the second, third etc. order of the light
intensity) optical phenomena have been discovered experimentally using powerful lasers [1, 2].
These so called many photon effects (second, third, and even higher order harmonic and sum
frequency generation, optical rectification, etc.) have found numerous applications. The
theoretical description of the linear and nonlinear optical properties of solids requires both
convenient and correct formalism, and a detailed quantum mechanical description of the many-
particle systems.
1.1 LINEAR OPTICAL PROPERTIES
The various ways in which light interacts with matter are of immense practical interest
e.g. absorption, transmission, reflection, scattering or emission. These properties are energy
dependent. The study of optical properties of solids has proven to be a powerful tool in our
understanding of the electronic properties of materials. In particular structure, energy
dependence of the properties mentioned above is in an intricate way related to the band structure.
Information on energy eigenvalues and Eigen function is needed to calculate the frequency /
energy dependent optical properties. When light of sufficient energy shines on a material, it
induces transitions of electrons from occupied states (below Fermi Energy, EF) to unoccupied
states (above EF). Clearly a quantitative study of these transitions must provide some
understanding of the position of the initial and the final energy bands and symmetry of their
associated wave functions.
7
1.2 Nonlinear optical properties A material interacting with intense light of a laser beam responds in a “nonlinear
fashion”. Consequences of this are a number of peculiar phenomena, including the generation of
optical frequencies that are initially absent. This effect allows the production of laser light at
wavelengths normally unattainable by conventional laser techniques. So the applications of Non
Linear Optics (NLO) range from basic research to spectroscopy, telecommunications and
astronomy.
Second harmonic generation (SHG), in particular, corresponds to the appearance of a
frequency component in the laser beam that is exactly twice the input one. SHG has great
potential as a characterization tool for materials, because of its sensitivity to symmetry. Today
SHG is widely applied for studying the surfaces and interfaces. For materials with bulk inversion
symmetry, SHG is only allowed at surfaces and interfaces. This makes SHG a powerful surface
selective technique. In case of embedded interfaces this technique gains extra weight when an
intense laser is used which is capable of penetrating deep into the material and no direct contact
with the sample is needed. In the case of linear optical transitions, an electron absorbs a photon from the incoming
light and makes a transition to the next higher unoccupied allowed state. When this electron
relaxes it emits a photon of frequency less than or equal to the frequency of the incident light
(Figure 1.a). SHG on the other hand is a two-photon process where this excited electron absorbs
another photon of same frequency and makes a transition to reach another allowed state at higher
energy. This electron when falling back to its original state emits a photon of a frequency which
is two times that of the incident light (Figure1.b). This results in the frequency doubling in the
output.
Figure 1. Schematic representation of (a) linear optical transition and
(b) second harmonic generation
8
In order to extend the use of NLO for understanding the properties of surfaces and for
extracting maximal information from such measurements for non centro-symmetric materials, a
more quantitative theoretical analysis is required.
1.3 Density Functional Calculations Density functional calculations (often called density functional theory (DFT)
calculations) are, like ab initio and SE calculations, based on the Schrodinger equation.
However, unlike the other two methods, DFT does not calculate a wavefunction, but rather
derives the electron distribution (electron density function) directly. A functional is a
mathematical entity related to a function. Density functional calculations are usually faster than
ab initio, but slower than SE. DFT is relatively new (serious DFT computational chemistry starts
in 1980' s, while computational chemistry with the ab initio and SE approaches was being done
in the 1960s).
Density functional theory is based on the Hohenberg-Kohn theorems, which state that,
“The ground-state properties of an atom or molecule are determined by its electron density
function, and that a trial electron density must give an energy greater than or equal to the true
energy”. DFT is not variational - it can give an energy below the true energy.
In the Kohn-Sham approach the energy of a system is formulated as a deviation from the
energy of an idealized system with non-interacting electrons. The energy of the idealized system
can be calculated exactly since its wavefunction (in the Kohn-Sham approach wavefunctions and
orbitals were introduced as a mathematical convenience to get at the electron density) can be
represented exactly by a Slater determinant. The relatively small difference between the real
energy and the energy of the idealized system contains the exchange-correlation functional, the
only unknown term in the expression for the DFT energy; the approximation of this functional is
the main problem in DFT. From the energy equation, by minimizing the energy with respect to
the Kohn-Sham orbitals, the Kohn-Sham equations (KS equations) can be derived, analogously
to the HF equations. The molecular orbitals of the KS equations are expanded with basis
functions and matrix methods are used to iteratively find the energy, and to get a set of molecular
orbitals, the KS orbitals, which are qualitatively similar to the orbitals of wave function theory.
The most popular current DFT method is the LSDA (Local Spin Density Approximation)
gradient-corrected hybrid method which uses the B3LYP (Becke three parameter Lee-Yang-
9
Parr) functional. For homolytic dissociation, correlated methods (e.g. B3LYP, pBP/DN* and
MP2) are vastly better than HF-level calculations; these methods also tend to give fairly good
activation barriers. DFT gives reasonable IR frequencies and intensities, comparable to those
from MP2 calculations. Dipole moments from DFT appear to be more accurate than those from
MP2. Time-dependent DFT (TDDFT) is the best method for calculating UV spectra reasonably
quickly. DFT is said to be better than HF (but not as good as MP2) for calculating NMR spectra.
1.4 Basis Sets An approximate wavefunction (eg. a Slater determinant) can be made up from MO’s
which are themselves approximated by atomic orbitals (LCAO). The AO’s are in turn
constructed from combinations of basis functions.
Basis functions AO’s MO’s Wave function
The list of all basis functions used in a calculation is called basis set.
The basis function model all the possible ways that electrons behave in a molecule. We should
include enough functions to model the orbital properly.
A basis set is a set of mathematical functions (basis functions), linear combinations of
which yield molecular orbitals. The functions are usually, but not invariably, centered on atomic
nuclei. Approximating molecular orbitals as linear combinations of basis functions is usually
called the LCAO or linear combination of atomic orbitals approach, although the functions are
not necessarily conventional atomic orbitals: they can be any set of mathematical functions that
are convenient to manipulate and which in linear combination give useful representations of
MOs. With this reservation, LCAO is a useful acronym. Physically, several (usually) basis
functions describe the electron distribution around an atom and combining atomic basis functions
yields the electron distribution in the molecule as a whole.
The electron distribution around an atom can be represented in several ways. Hydrogen-
like functions based on solutions of the Schrodinger equation for the hydrogen atom, polynomial
functions with adjustable parameters, Slater functions, and Gaussian functions have all been
used. Of these, Slater functions (STOs) and Gaussian functions (GTOs) are mathematically the
simplest, and it is these that are currently used as the basis functions in molecular calculations.
Slater functions are used in semi-empirical calculations. Modern molecular ab initio programs
employ Gaussian functions.
10
Slater Type Orbitals (STO) defined as,
Gaussian Type Orbitals (GTO) defined as,
where the radial part of the function, N is the
normalization factor, n is principal quantum number, is the angular part (spherical
harmonics), and Slater and Gaussian functions are usually characterized by parameters
designated ζ (zeta) and α, respectively.
Exponent ζ determines how fast or slow the basis function decays away from the atom.
Big ζ = fast decay = function close to nucleus; small ζ = slow decay = function far from nucleus.
The GTF’s have zero slope and no cusp at the nucleus. So GTF’s have problems
representing the proper behavior near the nucleus. GTF’s fall off too rapidly away from the
nucleus and the “tail” of the wave function is consequently represented poorly.
These problems can be solved by adding together several primitive Gaussians, called a
contraction, with different exponents and coefficients into one basis function to approximate the
shape.
1.4. a. Minimal Basis set
This basis set consists of one function each for the core orbitals and valence orbitals (whether
occupied or not).
Hydrogen 1s = one basis function; Fluorine 1s + 2s +2px + 2py + 2pz = five basis functions.
Carbon 1s + 2s +2px + 2py + 2pz = five basis functions. Unoccupied valence p orbital also
DFT studies on the electronic transitions of N-(4-Nitrophenyl)naphthalene-1-amine and
N-(2,4-dinitrophenyl)naphthalene-1-amine
DFT studies on the Non Linear Optical Properties of N-(4-Nitrophenyl)naphthalene-1-
amine and N-(2,4-dinitrophenyl)naphthalene-1-amine
Synthesis and characterization of N-(2,4-dinitrophenyl)naphthalene-1-amine.
14
CHAPTER 2
EXPERIMENTAL SECTION
15
2.1 Computational Details
Gaussian 09 software package was used for DFT calculation and calculations were
performed at B3LYP/6-31G(d,p) level. The ground state structures were optimized and
frequency calculations were performed to ensure that the optimized structures are minima in the
potential energy surface. HOMO and LUMO for all the molecules are identified. Gauss View 5
software was used for generating the input file and visualization of the results. The calculation
were done using S20D300 workstation computer equipped with Intel 7 core processor and 24 GB
RAM and Microsoft Windows as the operating system. Electric dipole moment, linear
polarizability and first hyperpolarizability tensor components for the studied compounds were
calculated by DFT approach which is currently one of the ultimate procedure for obtaining
numerically accurate NLO response.
2.2 Chemicals
1-Naphthylamine, 1-Fluoro-2,4-Dinitrobenzene and acetonitrile were purchased from Merck,
NH2
1-Naphthylamine NO2
NO2
F
1-Fluoro-2,4-Dinitrobenzene
2.3. Synthesis of N-(2, 4-dinitrophenyl)naphthalene-1-amine
Synthesis is based on the following equation.
NH2
NO2
NO2
F
+NaHCO3Acetonitrile
HN NO2
NO2
16
1 mol of 1-Naphthylamine(1.42 g) and 1 mol of 1-Fluoro-2,4-Dinitrobenzene (1 g) were taken in
250 ml RB flask.25 ml acetonitrile is added to it. The reaction mixture is refluxed at 80˚C for 10
hours. After refluxing, the reaction mixture is added to ice cold water. Reaction completion is
confirmed by TLC. N-(2,4-dinitrophenyl)naphthalene-1-amine is purified by Column separation.
Its formation is confirmed by FT-IR Spectrum.
2.4 Characterization Techniques
FT-IR: FT-IR spectra were recorded in the transmission mode using KBr pellets on Perkin
Elmer spectrometer operating at 4 cm-1 resolution at a range of 750 cm-1 to 4000 cm-1.
17
CHAPTER 3 RESULTS AND DISCUSSIONS
18
3.1 DFT studies on the electronic transitions of N-[3-(Naphthalene-1-yloxy)butyl]-2,4-dinitroaniline, N-[3-(Naphthalene-1-yloxy)butyl]-4-nitroaniline, and their azanaphthalene derivatives
The studied molecules are presented in Table 1-2.The study involves geometry optimization of the molecules, identifying its frontier molecular orbitals and energy gap. Electronic transitions of the following molecules are also discussed.
Figure 2. Schematic representation of naphthalene, quinoline, quinazoline, triaza naphthalene and tetraazanaphthalene derivatives linked to mononitrophenyl
R5
R8
R6
R7
R3
R2
R4
R1
O
CH3
NH
N+
O-
O Table 1. Structure of naphthalene, quinoline, quinazoline, triazanaphthalene and
tetraazanaphthalene derivatives linked to mononitrophenyl
No R1 R2 R3 R4 R5 R6 R7 R8 Name
1 C C C C C C C C N-[3-(Naphthalene-1-yloxy)butyl]-4-nitroaniline
2 C C C N C C C C N-[3-(Quinoline-4-yloxy)butyl]-4-nitroaniline
3 C N C N C C C C N-[3-(Quinazoline-1-yloxy)butyl]-4-nitroaniline
4 C N C N N C C C N-[3-(2,4,5TriazaNaphthalene-1-yloxy)butyl]-4-nitroaniline
5 C N C N N C N C N-[3-(2,4,5,7 TetraazaNaphthalene-1-yloxy)butyl]-4-nitroaniline
19
Figure 2. Schematic representation of naphthalene, quinoline, quinazoline, triazanaphthalene and tetraazanaphthalene derivatives linked to dinitrophenyl
R5
R8
R6
R7
R3
R2
R4
R1
O
CH3
NH
N+
O-
O
N+
O-
O Table 2. Structure of naphthalene, quinoline, quinazoline, triazanaphthalene and
tetraazanaphthalene derivatives linked to dinitrophenyl No R1 R2 R3 R4 R5 R6 R7 R8 Name 6 C C C C C C C C N-[3-(Naphthalene-1-yloxy)butyl]-2,4-dinitro
aniline 7 C C C N C C C C N-[3-(Quinoline-1-yloxy)butyl]-2,4-dinitro
aniline 8 C N C N C C C C N-[3-(Quinazoline-1-yloxy)butyl]-2,4-dinitro
aniline 9 C N C N N C C C N-[3-(2,4,5TriazaNaphthalene-1-yloxy)butyl]-
2,4-dinitroaniline 10 C N C N N C N C N-[3-(2,4,5,7 TetraazaNaphthalene-1-yloxy)
butyl]-2,4-dinitroaniline
20
3.1. a Geometry Optimization Several conformational isomeric cisoid and transoid structures of compound 1-10 were
optimized at B3LYP/6-31G (d,p) level. The lowest energy structures will be equilibrium
geometry of the molecules. The optimized molecular geometry (Fig.1-10) represents an isolated
molecule under ideal conditions with a stationary point at the potential energy surface. The
convergence was confirmed by observing no imaginary vibrational frequencies. All the
compounds in Table 1-2 show cisoid confirmation.
Table 3. Total energy and HOMO-LUMO gaps of compounds 1-5
Compound Total Energy Difference HOMO LUMO HLG
Hartrees kJ/Mol Hartrees Hartrees Hartrees eV 1
Cisoid
-1108.904369
10.75
-0.21101
-0.09895
0.11206
3.04
Transoid
-1108.908464
-0.20422
-0.07029
0.10397
3.64
2
Cisoid
-1124.962679
7.31
-0.22245
-0.07150
0.15095
4.11
Transoid
-1124.959894
-0.22341
-0.07283
0.15058
4.09
3
Cisoid
-1141.027722
6.14
-0.22071
-0.06992
0.1507
4.10
Transoid
-1141.025385
-0.22270
-0.07122
0.15148
4.12
4
Cisoid
-1157.07247
5.48
-0.22343
-0.07484
0.14859
4.04
Transoid
-1157.070381
-0.22519
-0.07327
0.15192
4.13
5
Cisoid
-1173.120091
6.04
-0.22564
-0.08870
0.13694
3.72
Transoid
-1173.117790
-0.22722
-0.08589
0.14133
3.85
21
Table 4. Total energy and HOMO-LUMO gaps of compounds 6-10
Table 7d. NLO Properties of Naphthalene/ Azanaphthalene linked to dinitrophenyl ring using B3LYP
Compound μ ˂α˃ a.u Δα a.u βtot a.u.
6 7.44 257.07 138.60 1467.67
7 7.05 257.86 236.46 1435.66
8 6.27 252.84 237.53 1528.13
9 5.56 247.75 229.99 1576.54
10 6.86 242.14 225.76 1543.95
Table 7e. NLO Properties of Naphthalene/ Azanaphthalene linked to dinitrophenyl ring using BPV86
Compound μ ˂α˃ a.u Δα a.u βtot a.u.
6 7.47 265.89 148.78 1579.02
7 7.03 267.38 250.26 1681.89
8 6.25 262.51 251.86 1856.31
9 5.63 257.42 244.099 1896.38
10 6.92 251.77 240.10 1820.16
Table 7f. NLO Properties of Naphthalene/ Azanaphthalene linked to dinitrophenyl ring using LSDA
Compound μ ˂α˃ a.u Δα a.u βtot a.u.
6 7.5835 266.34 150.15 1716.427
7 7.1259 268.01 252.03 1696.445
8 6.3503 263.18 253.72 1969.049
9 5.6991 258.07 245.89 2000.946
10 7.0256 252.45 241.98 1909.016
The discussion will be focused mostly on the first hyperpolarizability because the main objective of this work is to describe a general mechanism for obtaining large first-order optical nonlinearities in substituted naphthalene and azanaphthalene derivatives.
29
Graph 1. Comparison of first hyperpolarizability for compounds 1-5
2 4
2400
3200
4000
hype
rpol
arizi
bility
COMPOUNDS
LSDA BPV86 B3LYP
Graph 2. Comparison of first hyperpolarizability for compounds 6-10
1 2 3 4 51400
1500
1600
1700
1800
1900
2000
Hype
rpol
arizi
biliti
es
compounds
B3LYP BPV86 LSDA
In particular, the results of the calculations showed that the magnitudes of hyperpolarizibilities
are mainly dependent on the degree of electron delocalization between the two rings. Optical
response properties are governed by the increasing of both conjugation length and strength of
donor and acceptor groups. Also, the nitrogen numbers, planarity of the rings with spacer and
30
positions on the naphthalene are very important for nonlinearity of the title molecules.
Theoretically, the torsional angles between the planes of the donor and acceptor subunits are
calculated. Angle between C11-O1-C7-C8 determines the planarity of naphthalene ring with
spacer. Also the distance between C7-C15 is measured. They are shown in Figure 3-4.The
torsional angles and effective distance between two rings are enlisted in Table 8.
Figure 4. Naphthalene/Azanaphthalene linked to mononitrophenyl ring
31
Figure 5. Naphthalene/Azanaphthalene linked to dinitrophenyl ring
Table 8. Comparison of first hyperpolarizability for compounds 1-10 using B3LYP, BPV86 and LSDA and some selected geometrical parameters. β (B3LYP) β (BPV86) β (LSDA) C7-C15 (Å) C11-O1-C7-C8 (˚)
1 2026.33 2223.519 2271.065 6.89 2.434
2 2339.597 2536.114 2565.476 6.47 1.434
3 2386.487 2564.504 2599.997 6.433 1.280
4 2306.046 2474.841 2499.029 6.435 1.679
5 1963.409 1948.879 1938.155 6.434 2.884
6 1467.674 1579.016 1716.427 4.503 1.273
7 1435.662 1681.891 1696.445 5.779 3.277
8 1528.128 1856.31 1969.049 5.891 0.900
9 1576.539 1896.384 2000.946 5.924 0.692
10 1543.95 1820.155 1909.016 5.979 0.978
32
From this table, it is evident that the effective distance between two rings for mononitro
derivatives are larger than dinitro derivatives. As the effective distance increases, it is believed
that the extent of delocalization increases. So mononitro compounds are having large β values
than dinitro compounds. Addition of nitrogen on naphthalene changes the torsional angle
between the two units. However in all 10 compounds, naphthalene ring remains coplanar with
the spacer group. Among 10 selected compounds, compound no.3 is having highest β.This can
be attributed to its large delocalization and coplanarity of the ring with the spacer group.
3.3 DFT studies on the electronic transitions of N-[3-(Quinoline-1-yloxy)butyl]-2,4-dinitroaniline, N-[3-(Quinoline-1-yloxy)butyl]-4-nitroaniline, and their position isomers
The studied molecules are presented in Table 10-11.The study involves geometry optimization of
the molecules, identifying its frontier molecular orbitals and energy gap. Electronic transitions of
the following molecules are also discussed.
Figure 6. Schematic representation of naphthalene, quinoline, quinazoline, triazanaphthalene and tetraazanaphthalene derivatives linked to mononitrophenyl
R5
R8
R6
R7
R3
R2
R4
R1
O
CH3
NH
N+
O-
O
33
Table 9. Structure of naphthalene, quinoline, quinazoline, triazanaphthalene and tetraazanaphthalene derivatives linked to mononitrophenyl
No R1 R2 R3 R4 R5 R6 R7 R8 Name
1 C C C N C C C C N-[3-( Quinoline-2-yloxy)butyl]-4-nitroaniline
2 C C C N C C C C N-[3-(Quinoline-4-yloxy)butyl]-4-nitroaniline
3 C C C N C C C C N-[3-( Quinoline-6-yloxy)butyl]-4-nitroaniline
4 C C C N C C C C N-[3-( Quinoline-8-yloxy)butyl]-4-nitroaniline Figure 7. Schematic representation of naphthalene, quinoline, quinazoline,
triazanaphthalene and tetraazanaphthalene derivatives linked to dinitrophenyl
R5
R8
R6
R7
R3
R2
R4
R1
O
CH3
NH
N+
O-
O
N+
O-
O Table 10. Structure of naphthalene, quinoline, quinazoline, triazanaphthalene and
tetraazanaphthalene derivatives linked to dinitrophenyl No R1 R2 R3 R4 R5 R6 R7 R8 Name 5 C C C N C C C C N-[3-( Quinoline-2-yloxy)butyl]-2,4-dinitroaniline 6 C C C N C C C C N-[3-(Quinoline-4-yloxy)butyl]- 2,4-dinitroaniline 7 C C C N C C C C N-[3-( Quinoline-6-yloxy)butyl]- 2,4-dinitroaniline 8 C C C N C C C C N-[3-( Quinoline-8-yloxy)butyl]- 2,4-dinitroaniline
34
3.3.a Geometry Optimization Several conformational isomeric cisoid and transoid structures of compound 1-10 were
optimized at B3LYP/6-31G(d,p) level. The lowest energy structures will be equilibrium
geometry of the molecules. The optimized molecular geometry (Fig.3-4) represents an isolated
molecule under ideal conditions with a stationary point at the potential energy surface. The
convergence was confirmed by observing no imaginary vibrational frequencies. All the
compounds in Table 10-11 show cisoid confirmation.
Table 11a. Total energy and HOMO-LUMO gaps of compounds 1-4 Compound Total Energy Difference HOMO LUMO HLG
All the compounds show Cisoid confirmation and their energy gap between HOMO and LUMO is identified
38
3.3 DFT studies on the electronic transitions of N-[3-(Quinoline-1-yloxy)butyl]-2,4-dinitroaniline, N-[3-(Quinoline-1-yloxy)butyl]-4-nitroaniline, and their position isomers
The simplest polarizability, a, characterizes the ability of an electric field to distort the
electronic distribution of a molecule, that is, the molecule as a whole is perturbed. Consequently,
a change in the equilibrium nuclear geometry will take place as a result of the development of a
different potential-energy surface. The result would be a change in the vibrational and rotational
motions of the molecule.Clearly, an effect of such orientation redistribution cannot be ignored.
Higher order polarizabilities (hyperpolarizabilities β,γ. . .) which describe the non-linear
response of atoms and molecules are related to a wide range of phenomena from non-linear
optics to intermolecular forces, such as the stability of chemical bonds, as well as, the
conformation of molecules and molecular aggregates [23].
According to Buckingham [24] the polarizability tensors are formally defined by a Taylor
series expansion of the dipole moment of a molecule in the presence of an electric field E,
0
( ) ( )
1 1 .........,2! 3!
E E
E E E E E E
λ λ
λ λ λσ σ λσν σ ν λσνρ σ ν ρ
µ ψ µ ψ
µ µ α β γ
∧
=
= + + + +
Where, μ is the dipole polarizability, β is the hyperpolarizability and γ is the second
hyperpolarizability and so on.; These studies led to the fact that ab initio calculations of
polarizabilities and hyperpolarizabilities have become available through the strong theoretical
basis for analyzing molecular interactions. They made possible the determination of the elements
of these tensors from derivatives of the dipole moment with respect to the electric field. For
methods as the self-consistent field (SCF) for which the wave function obeys the Hellmann–
Feynman theorem, the derivative expression for the dipole is equivalent to the expectation value
[25]. Applying the rules of perturbation theory, α and β are determined from a knowledge of the
first-order wave function and γ from a knowledge of the second-order wave function. Thus they
may be calculated accurately at the self-consistent field level using the Hartree–Fock theory [26].
However, electron correlation can be very important [27, 28] depending on whether it is an open
or closed shell system [29,30].
39
Table 14a. NLO Properties of N-[3-(Quinoline-1-yloxy)butyl]-4-nitroaniline, and their position isomers
Compound μ ˂α˃ a.u Δα a.u βtot a.u.
1 8.0318 245.8515 306.8861 2118.192
2 5.4716 243.0167 283.3157 2339.597
3 9.8753 245.9185 309.2144 1777.295
4 8.8968 239.2811 233.0332 1981.583
Table 14b. NLO Properties of N-[3-(Quinoline-1-yloxy)butyl]-2,4-dinitroaniline, and their position isomers
Compound μ ˂α˃ a.u Δα a.u βtot a.u.
5 9.7377 262.4461 216.0226 1816.091
6 7.0527 257.8592 236.4552 1435.662
7 7.2650 260.5112 254.3742 2016.854
8 11.1655 259.1174 220.2316 1612.477
All the 8 compounds show high β values which means they can be developed into good NLO
materials.
40
3.5 DFT studies on the electronic transitions of N-[(Naphthalen-5-yl)methyl]-4-nitrobenzamine and N-[(Naphthalen-5-yl)methyl]-2,4 dinitrobenzamine
HN
NO2
N-[(Naphthalen-5-yl)methyl]-4 nitrobenzamin
HN
NO2
NO2
N-[(Naphthalen-5-yl)methyl]-2,4 dinitrobenzamine
3.5.1 Geometry Optimization
Several conformational isomeric cisoid and transoid structures of compound 1 and 2
were optimized at B3LYP/6-31G(d,p) level. The lowest energy structures will be equilibrium
geometry of the molecules. The optimized molecular geometry (Fig.8) represents an isolated
molecule under ideal conditions with a stationary point at the potential energy surface. The
convergence was confirmed by observing no imaginary vibrational frequencies. All the
compounds in show cisoid confirmation.
Table 15. Total energy and HOMO-LUMO gaps of compounds 1-2 Compound Total Energy Difference HOMO LUMO HLG
N-[(Naphthalen-5-yl)methyl]-4 nitrobenzamine and N-[(Naphthalen-5-yl)methyl]-2,4
dinitrobenzamine shows cisoid conformation. Their frontier molecular orbitals are identified and
they are enlisted in Table 18.
Table 17. HOMO-LUMO Orbitals of compound 1-2
Compound HOMO Orbital LUMO Orbital 1
2
42
3.6 DFT studies on the nonlinear optical properties of N-[(Naphthalen-5-yl)methyl]-4 nitrobenzamine and N-[(Naphthalen-5-yl)methyl]-2,4 dinitrobenzamine
The simplest polarizability, a, characterizes the ability of an electric field to distort the
electronic distribution of a molecule, that is, the molecule as a whole is perturbed. Consequently,
a change in the equilibrium nuclear geometry will take place as a result of the development of a
different potential-energy surface. The result would be a change in the vibrational and rotational
motions of the molecule. Clearly, an effect of such orientation redistribution cannot be ignored.
Higher order polarizabilities (hyperpolarizabilities β,γ. . .) which describe the non-linear
response of atoms and molecules are related to a wide range of phenomena from non-linear
optics to intermolecular forces, such as the stability of chemical bonds, as well as, the
conformation of molecules and molecular aggregates
Dipole moment, sotropic polarizability, anisotropic polarizability and hyper polarizability are
calculated using the aforementioned equation and were enlisted in Table 18.
Table 18: NLO properties of N-[(Naphthalen-5-yl)methyl]-4 nitrobenzamine and N-