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R.N. Singh et al. / Journal of Molecular Structure 1052 (2013) 67–75
opto-electronic [33] and non-linear optical (NLO) response [34].
The development of organic NLO materials for device applications
requires multidisciplinary effort involving both theoretical and
experimental studies. Quantum-chemical calculations have made
an important contribution to the understanding of the electronic
polarization underlying the molecular NLO processes and the
establishment of structure–property relationships [35,36]. Organic
molecules with large second-order NLO are the subject of substan-
tial research due to their potential applications in optical modula-
tion, molecular switching, optical memory, and frequency doubling
[37–42]. Nonlinearity in organic molecules can be synthetically
modulated by varying the composition or length of conjugated
3. Quantum chemical calculations
All the quantum chemical calculations have been carried out
with Gaussian 09 program package [43] using DFT method,
B3LYP functional and 6-31G(d,p) basis set to predict the molecu-
lar structure, 1H NMR chemical shifts, vibrational wavenumbers,
electronic transitions, electronic reactivity descriptors and first
hyperpolarizability. B3LYP invokes Becke’s three parameter (local,
non local, Hartree–Fock) hybrid exchange functional (B3) [44],
with Lee–Yang–Parr correlational functional (LYP) [45]. The basis
set 6-31G(d,p) with ‘d’ polarization functions on heavy atoms and
‘p’ polarization functions on hydrogen atoms are used for better
description of polar bonds of molecule [46,47]. The ‘p’ polariza-
tion functions on hydrogen atoms are used for reproducing the
out of plane vibrations involving hydrogen atoms. The motivation
to use B3LYP functional and the bases set 6-31G (d,p) for the the-
oretical calculations is due to ability to successfully predict a
wide range of molecular properties of hydrogen bonded com-
plexes at a relatively low computational cost. To estimate the en-
thalpy (H) and Gibbs free energy (G) values, thermal corrections
to the enthalpy and Gibbs free energy are added to the calculated
total energies. Time dependent density functional theory (TD-
DFT) is used to find the various electronic excitations and their
nature within molecule. The second-order Fock matrix was used
to evaluate the donor–acceptor interactions in the NBO basis
[48]. For each donor (i) and acceptor (j), the stabilization energy
E(2) associated with the delocalization i ? j is estimated using
equation [49,50] as:
p-systems, and by evaluating the effects of various electron-donor
and -acceptor groups. Although, organic molecules are not as
robust as inorganics, they have received a great deal of interest
in the non-linear optics field and they offer many advantages over
traditional inorganic crystals: (i) organic materials show high
molecular hyperpolarizability and fast response time; (ii) they
are cheaper to produce and easier to fabricate; and (iii) their struc-
tures can be modified in numerous ways allowing to finely tune
NLO properties for desired applications.
In observation of above applications of dipyrromethanes and
hydrazide–hydrazones, hydrazide–hydrazones containing dipyr-
romethane:
1,9-bis[(4-isonicotinoyl)-hydrazonomethyl]-5-phe-
nyl-dipyrromethane (3) has been synthesized and characterized
using experimental measurement (1H NMR, UV–Visible, FT-IR,
Mass spectroscopic techniques) and quantum chemical calcula-
tions. The nature of chemical reactivity and site selectivity of this
molecule has been determined on the basis of Global and Local
reactivity descriptors. The first hyperpolarizability (b0) has been
computed to indicate suitability for non-linear optical response.
2
Eð2Þ ¼
D
Eij ¼ qiððFði; jÞ =ðej
ꢃ
e0iÞÞÞ
where qi is the donor orbital occupancy, ei and ej are diagonal ele-
ments and F(i, j) is the off-diagonal NBO Fock matrix element be-
tween i and j NBO orbitals.
Potential energy distribution along internal coordinates has
been calculated by Gar2ped software [51]. Global reactivity
2. Experimental details
2-[(4-Isonicotinoyl)-hydrazonomethyl]-1H-pyrrole (1) was
prepared by stirring the equimolar reaction mixture of pyrrole-2-
carboxaldehyde and isonicotinic acid hydrazide at room tempera-
ture. Benzaldehyde (2) was purchased from commercial source.
The Mass spectrum of (3) was recorded on JEOL-Acc TDF JMS-
T100LC, Accu TOF mass spectrometer. The 1H NMR spectrum of
(3) was recorded in MeOD on Bruker DRX-300 spectrometer using
TMS as an internal reference. The FT-IR spectrum was recorded in
KBr medium on a Bruker spectrometer. The UV–Visible absorption
spectrum of (3), (1 ꢄ 10ꢃ5 M in MeOD) was recorded on ELICO
SL-164 spectrophotometer.
descriptors [52–56]: electronegativity (
global hardness ( ), global softness (S) and electrophilicity index
) are highly successful in predicting global reactivity trends
and calculated using the following equations: LUMO + -
= ꢃ1/2(
HOMO); = 1/2 (eLUMO HOMO); = 1/2 (eLUMO HOMO); S = 1/2
2/2
. The local reactivity descriptors [52,56] such as Fukui
v), chemical potential (l),
g
(x
v
e
e
l
+
e
g
ꢃ
e
g;
x
=
l
g
functions fkþðrÞ, fkꢃðrÞ, fk0ðrÞ calculated using the following equa-
tions: fkþðrÞ ¼ ½qNþ1ðrÞ ꢃ qNðrÞꢅ ¼ ½qkðN þ 1Þ ꢃ qkðNÞꢅ, for nucleo-
philic attack; fkꢃðrÞ ¼ ½qNðrÞ ꢃ qNꢃ1ðrÞꢅ ¼ ½qkðNÞ ꢃ qkðN ꢃ 1Þꢅ, for
electrophilic attack; fk0ðrÞ ¼ 1=2½qNþ1ðrÞ þ qNꢃ1ðrÞꢅ ¼ 1=2½qkðNþ
1Þ þ qkðN ꢃ 1Þꢅ, for radical attack, where,
q is the electron density
of atom k in the molecule, q is the gross charge of atom k in the
molecule and N, N + 1, N ꢃ 1 are electron systems containing neu-
tral, anion, cation form of molecule, respectively. Using Fukui func-
tions, other local reactivity descriptors: local softnesses ðsþk ; skꢃ; sk0Þ
2.1. Synthesis of 1,9-bis[(4-isonicotinoyl)-hydrazonomethyl]-5-
phenyl-dipyrromethane (3)
and electrophilicity indices ðxkþ
;
xkꢃ
;
x0kÞ are calculated using fol-
To the solution of 2-[(4-isonicotinoyl)-hydrazonomethyl]-1H-
pyrrole (0.200 g, 0.93420 mmol) and benzaldehyde (0.0495 g,
0.047 ml, 0.46713 mmol) in 25 ml methanol conc. HCl (0.001 ml)
was added as catalyst. The reaction mixture was refluxed for
12 h; the color of reaction was changed to dark brown. The com-
pletion of reaction was monitored by thin layer chromatography
(TLC). Now, the reaction mixture was treated with saturated aque-
ous solution of sodium bicarbonate (NaHCO3) and extracted with
dichloromethane (30 ml ꢄ 4). The organic layer was dried over
MgSO4 and solvent was removed under reduced pressure. The
formed solid was purified by column chromatography using
hexane, dichloromethane as eluent and the pure product (3) was
obtained. Color: dark brown; Yield: 67.50%; MS for C29H24N8O2:
Calcd. 516.20 amu, Obs. m/z 517.21 [M+ + 1]. Elemental analysis
for C29H24N8O2: Calcd. C 67.41, H 4.68, N 21.70, Obs. C 67.38, H
4.72, N 21.67%.
lowing equations: sþk ¼ Sfkþ; skꢃ ¼ Sfꢃk ; s0k ¼ Sfk0; xþk
¼
x
fkþ; xꢃk
¼
x
fkꢃ; x0k
¼
x
fk0, where; +, ꢃ and 0 sign show nucleophilic, electro-
philic and radical attack, respectively.
The total static dipole moment (
l0), mean polarizability (|a0|),
anisotropy of polarizability ( ) and first hyperpolarizability (b0)
D
a
are calculated using x, y, z components by following equations
[57–60]
1=2
l0 ¼ ðl2x
þ
ly2
þ
þ
lz2
ayy
Þ
ja0j ¼ 1=3ðaxx
þ
azz
Þ
D
a
¼ 2ꢃ1=2½ðaxx
ꢃ
ayyÞ þ ½ðayy
ꢃ
azzÞ þ ðazz
ꢃ
axxÞ þ 6a2xxꢅ1=2
2
2
2
1=2
2
2
2
b0 ¼ ½ðbxxx þ bxyy þ bxzzÞ þðbyyy þ bxxy þ byzzÞ þðbzzzþbxxz þ byyzÞ ꢅ
Singh
