456
E.E. Porchelvi, S. Muthu / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 134 (2015) 453–464
Table 1 (continued)
Parameters
Experimentala
Theoretical
Parameters
Experimentala
Theoretical
B3LYP/6-311++G(d,p)
B3LYP/6-311++G(d,p)
C2–C3–O4
C2–C3–C5
C2–C8–C7
115.9
120.8
122.6
117.6
121.0
121.9
H33–C20–H35
H34–C20–H35
108.9
109.0
107.9
107.2
a
Data from Ref. [16].
character. From the theoretical values, we found most of the opti-
mized bond lengths are in good agreement with experimental
bond lengths but bond angles are slightly longer and shorter than
that of experimental values. The small deviations are probably due
to the intermolecular interactions in the crystalline state of the
molecule.
The intermolecular hyperconjugative interactions are formed by
the orbital overlap between bonding (C–C), (C–S), (C–H), (C–N),
(C–O) and (O–H) and antibonding (C–C), (C–S), (C–H), (C–N),
(C–O) and (O–H) orbital which results in intramolecular charge
transfer (ICT) causing stabilization of the molecular system. These
interactions are observed as an increase in electron density (ED) in
the (C–C), (C–S), (C–H), (C–N), (C–O) and (O–H) antibonding orbital
that weakness the respective bonds. The electron density of the
two conjugated single as well as double bond of SMPTSC (ꢃ1.9e)
clearly demonstrate strong delocalization. The strong intramolecu-
lar hyper conjugative interactions of the and electrons of (C–C),
(C–S), (C–H), (C–N), (C–O) and (O–H) to the antibonding of
((C–C), (C–S), (C–H), (C–N), (C–O) and (O–H) bonds of the ring lead
to stabilization of some part of the ring as shown in Table 2. The
strong intramolecular hyperconjugative interaction of and elec-
trons of C–C to anti C–C bond of the ring leads to stabilization of
some part of the ring as evident from Table 2. For example the
Prediction of hyperpolarizability
The NLO activity provide the key functions for frequency shift-
ing, optical modulation, optical switching and optical logic for the
developing technologies in areas such as communication, signal
processing and optical interconnections [17,18]. Hyperpolarizabil-
ities are very sensitive to basis sets and levels of theoretical com-
putations employed [19,20] that the electron correlation can
change the value of hyperpolarizability. The highest value of the
dipole moment is found along
ly. The direction of the ly value is
intramolecular hyperconjugative interaction of
r(C3–C5) distrib-
2.8287D as shown in Table S1. For the direction x and z the values
are ꢂ4.9455 and 0.2940D respectively. The first order hyperpolar-
izability (btotal) value of SMPTSC is calculated to be 2.3332Eꢂ29 esu
as shown in Table S1.
ute to rꢁ(C2–C3), (C5–C6), (C1–C2) leading to stabilization of
6.79 KJ/mol. This enhanced further conjugation with antibonding
orbital of
p(C3–C5) which leads to strong delocalization of
24.32 KJ/mol with pꢁ(C6–C7) respectively. The most important
highest energy, related to the molecule is electron donating from
r
NBO analysis
(C17–C20) to the antibonding acceptor rꢁ(C17–C20) with stabiliza-
tion energy 2147 KJ/mol. The magnitude of charge transferred
from N10 LP(1) to the antibonding C11 LP(1)ꢁ and N13 LP(1) to the
antibonding C11 LP(1)ꢁ shows that stabilization energy 133.11 KJ/
mol and 135.58 KJ/mol.
NBO analysis provides the most accurate possible ‘natural Lewis
structure’ picture of /, because all orbital details are mathemati-
cally chosen to include the highest possible percentage of the elec-
tron density. A useful aspect of the NBO method is that it gives
information about interactions in both filled and virtual orbital
spaces that could enhance the analysis of intra- and intermolecular
interactions.
Vibrational analysis
The second order fock matrix was carried out to evaluate the
donor–acceptor interactions in the NBO analysis [21]. The interac-
tions result is a loss of occupancy from the localized NBO of the
idealized Lewis structure into an empty non-Lewis orbital. For each
donor (i) and acceptor (j), the stabilization energy E[2] associated
with the delocalization i ? j is estimated as
The molecule SMPTSC consists of 35 atoms, so it has 99 normal
vibrational modes. The vibrational spectral assignments have been
carried out with the assist of NCA. The internal coordinates for
SMPTSC were defined as given in Table S2 and are summarized
in Table S3 according to Pulay’s recommendation. The calculated
wave numbers related to the observed peaks are shown in Table 3
along with detailed assignments. For visual comparison, the
observed and stimulated FT-IR and FT-Raman spectra of title
compound are presented in Figs. 2 and 3 respectively.
2
Fði; jÞ
E2 ¼ Eij ¼ q
D
i Ei ꢂ Ej
where qi is the donor orbital occupancy, Ej and Ej are diagonal
elements and F(i,j) is the off diagonal NBO Fock matrix element.
Natural bond orbital analysis provides an efficient method for
studying intra- and intermolecular bonding and interaction among
bonds and also provides a convenient basis for investigating charge
transfer or conjugative interaction in molecular systems. Some elec-
tron donor orbital, acceptor orbital and the interacting stabilization
energy resulting from the second-order micro-disturbance theory
are reported [22,23].
The larger the E(2) value, the more intensive is the interaction
between electron donors and electron acceptors. Delocalization
of electron density between occupied Lewis-type (bond or lone
pair) NBO orbitals and formally unoccupied (antibond or Rydberg)
non-Lewis NBO orbital correspond to a stabilizing donor–acceptor
interaction. NBO analysis has been performed on the molecule at
the DFT/B3LYP/6-31 + G(d,p) level in order to elucidate the intra-
molecular, delocalization of electron density within the molecule.
C–H vibrations
The hetero aromatic structure shows the presence of C–H
stretching vibrations in the region 3100–3000 cmꢂ1 which is the
characteristic region for the ready identification of C–H stretching
vibrations [24]. In this region, the bands are not affected apprecia-
bly by the nature of substituent. In the FT-IR and FT-Raman the
bands observed at 3197, 3166, 3147, 3136, 2984, 2917,
2848 cmꢂ1 and 3192, 3175, 3139, 3130, 3063, 2919 cmꢂ1 respec-
tively are assigned to the C–H stretching vibrations of SMPTSC.
The in-plane C–H bending vibrations normally appear in the range
1000–1300 cmꢂ1 in the substituted benzenes and the out of plane
bending vibrations occur in the region 750–1000 cmꢂ1 region
[25,26]. In this study, the C–H in-plane bending vibrationsꢂ1are
assigned to 1207, 1201, 1154, 1146, 1117, 1080, 1032 cm in
FT-IR and 1199, 1149, 1145, 1140, 1134, 1075, 1060 cmꢂ1 in