# Quantum Chemical and Spectroscopic Investigations of (Ethyl 4 hydroxy-3-((E)-(pyren-1-ylimino)methyl)benzoate) by DFT Method

Authors: Diwaker; Abhishek Kumar Gupta
Journal: International Journal of Spectroscopy
 (2014)

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## Abstract

In the present work we have reported the optimized ground state geometry, harmonic vibrational frequencies, NMR chemical shifts, NBO analysis, and molecular electrostatic potential surface map of the title compound using DFT/B3LYP/6-311++G(2d, 2p) level of theory. We have compared our calculated results with the experimentally obtained values and found that both are in close agreement with each other. We have used the gauge-invariant atomic orbital (GIAO) approach to calculate the NMR (13C and 1H) chemical shifts using Gaussian 09 package. TD-DFT (time-dependent DFT) approach has been used to simulate the electronic spectra of the title compound in order to account for excited states. Other molecular properties such as HOMO-LUMO energies, NBO analysis, and PED distribution analysis have been studied and reported using DFT/B3LYP/6-311++G(2d, 2p) level of theory.


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## Body

## 1. Introduction

The title compound chosen for DFT studies to extract different molecular properties has been experimentally synthesized and prepared using 1 amino pyrene and (ethyl 3-formyl-4-hydroxybenzoate) at room temperature for six hours in the presence of dry MeOH [1]. The title compound shows sensing properties for selective detection of niobium ions in mixed aqueous media. In the literature survey we found that there are lot of research articles based upon fluorescent techniques for detection of various metal ions, however literature survey also reveals very few ab initio HF/MP2/DFT calculations of such type of compounds. Fluorescence is a very simple technique and acts as a convenient characterization tool for detection of very small amount (in ppm) of various metal ions in solutions [2]. From application point of view niobium metal is used in various kinds of applications such as superconducting magnets [3] and biological applications [4]. In interest of such applications the quantum mechanical calculations of the title compound are thoroughly investigated. The aim of this work is to predict the structural, electronic, vibrational, and spectral parameters and other molecular properties of the title compound using DFT approach [5–9].


## 2. Experimental Details

In this section we have reported short details about the methodology and characterization tools used for the title compound, however we advised the readers to consult [1] for more details. The chemical structure and fluorescent properties of the title compound are confirmed by single crystal X-ray diffraction, UV spectra, 1H and 13C NMR, and FTIR spectra. 1H and 13C NMR are recorded in chloroform using TMS as internal standard on a Varian Mercury 300 spectrometer operating at 300 MHz for 1H and 75 MHz for 13C. IR spectra are recorded on a Perkin-Elmer PE-983 infrared spectrometer as KBr pellets with absorption reported in cm−1. The ultraviolet absorption spectra were recorded on Shimadzu UV-2450 spectrophotometer. Fluorescent spectra measurements were performed on Agilent Technologies Cary Eclipse fluorescence spectrometer.


## 3. Computational Details

Using DFT/B3LYP/6-311++G(2d, 2p) level of theory [10] we have investigated the ground state optimized geometry of the title compound. The molecular geometry is fully optimized using tight convergence criteria along with redundant internal coordinates and Berny’s optimization algorithm. The optimized parameters obtained using DFT approach have been compared with the experimental values and are in close agreement with them. Further we have used the optimized ground state geometry of the title compound to study the different properties like NMR spectra, UV-Vis spectra, MEP surface mapping, PED analysis, and NBO analysis. Using DFT/B3LYP/6-311++G(2d, 2p) level of theory and GAIO (Gauge-Invariant Atomic Orbital) [11, 12] approach we have reported the NMR (13C and 1H) chemical shifts of the title compound and compared them with their experimental counterparts. To study the electronic transitions and excited states we have used the TD-DFT (time-dependent) method available in Gaussian 09 package. HOMO-LUMO energies are also calculated at DFT/B3LYP/6-311++G(2d, 2p) level of theory. Vibrational wavenumbers assignment is done by using VEDA 4 program. MEP surface mapping is investigated to comment upon the reactive nature of the title compound. In order to find out the various interactions between the filled and the vacant orbitals, NBO analysis [13] of the title compound has been done using NBO 3.1 program available in Gaussian 09 package at DFT/6-311++G(2d, 2p) level of theory. The unoptimized structure of our title compound is presented in Figure 1.Figure 1
Structure of new Schiff base ((ethyl 4 hydroxy-3-((E)-(pyren-1-ylimino)methyl)benzoate) using hyperchem.


## 4. Results and Discussion

### 4.1. Molecular Geometry

We have used the DFT/B3LYP/6-311++G(2d, 2p) level of theory available in Gaussian 09 program to investigate the ground state geometry of the title compound. The geometry is fully optimized with tight convergence criteria and the structure is local minima on the PES. On comparison with the experimentally obtained parameters one can conclude that our calculation is successful, as the difference between calculated and experimental bond lengths, bond angles is of few Å. Figure2 represents the stable conformation of the title compound using DFT calculations. The selected calculated bond lengths (R) and angles (Å) for the title compound along with their corresponding experimental values are listed in Table 1.Table 1
The selected calculated and experimental values [1]* for the stable conformation of the title compound.
Serial number
R (bond length/angstrom)
Calculated
Experimental
1
R (3, 12)
1.36
1.35
2
R (7, 8)
1.24
1.23
3
R (13, 14)
1.30
1.29
4
R (9, 7)
1.37
1.34
5
R (9, 10)
1.48
1.45
6
R (14, 15)
1.41
1.41
Serial number
A (angle/degrees)
Calculated
Experimental
1
A (13-14-15)
121.30
120.98
2
A (12-3-4)
121.10
120.37
3
A (8-7-6)
124.98
124.94
4
A (9-10-11)
106.83
106.84
5
A (7-9-10)
117.12
117.78
6
A (12-3-2)
118.82
118.86
7
A (8-7-9)
122.09
123.01
8
A (9-7-6)
112.92
112.95
R: Bond lengths (in Angstrom); A: Angles (in Degrees).Figure 2
Stable structure of new Schiff base using DFT approach with energy = −1282.65751536 au.Correlation between [14] the calculated and the experimental parameters of bond lengths and bond parameters for the title compound are shown in Figure 3. Bond length and bond angles correlation R2 values are 0.9802 and 0.9921, respectively.Correlation between the calculated and the experimental values of the (a) bond angles and (b) bond length for the stable conformation of the title compound.
(a)
(b)


### 4.2. Chemical Shifts

NMR spectroscopy is considered as a valuable tool for the structural and functional characterization of molecules.1H and 13C NMR chemical shifts of the title compound are investigated using DFT/B3LYP/6-311++G(2d, 2p) level of theory with GIAO (gauge-invariant atomic orbital) approach in DMSO. The calculated 1H and 13C NMR chemical shifts of the title compound together with the corresponding experimental values are shown in Tables 2 and 3 as values relative to tetramethylsilane. The 1H NMR spectra of the title compound in DMSO show a triplet peak in the range from 1.36 to 1.40 ppm for C–CH3 and quartet peak in the range from 4.32 to 4.38 ppm for O–CH2. Corresponding calculated values are in the range from 1.31 to 1.46 ppm and 4.27 to 4.32 ppm, respectively. Aromatic protons in pyrene appeared in the range from 8.04 to 8.48 ppm with calculated values ranging from 8.32 to 9.03 ppm. Aromatic protons in substituted benzene showed a singlet peak at 8.66 ppm and doublet at 8.50 ppm and 7.16 ppm. Corresponding calculated values are 8.66 ppm, 8.50 ppm, and 7.44 ppm, respectively. Proton of Schiff base shows a singlet peak at 9.37 ppm while calculated value is at 9.34 ppm. The 13C NMR spectra of the title compound in DMSO showed a peak at 14.44 ppm for C–CH3 (calculated value as 13.48 ppm), at 60.99 ppm for O–CH2 (calculated value as 60.56 ppm), at 165.88 ppm for C=O (calculated value as 180.00 ppm), and at 162.81 ppm for C=N (calculated value as 169.94 ppm). Aromatic carbons of pyrene and substituted benzene showed peaks in the range from 115.67 to 165.12 ppm while calculated values are in the range from 121.53 to 175.80 ppm. We have also reported the hydrogen and carbon NMR chemical shifts by IGAIM and CGST methods using B3LYP/6-311++G(2d, 2p) basis sets [15]. From the comparison table we can conclude that theoretical values for carbon and hydrogen NMR chemical shifts calculated by GIAO method are in close agreement as compared to other CGCST and IGAIM methods. Linear correlation coefficients (R2) for linear regression analysis of theoretical and experimental values of 1H and 13C NMR chemical shifts using GIAO method are found to be 0.9959 and 0.9958 respectively.Table 2
Comparison of DFT/B3LYP/6-311++G (2d, 2p) calculated and experimental values [1]* of 1H chemical shift (ppm) relative to the TMS for the title compound.
Atom
Experimental value
6311++G
6311++G
6-311++G
(2d, 2p)/GIAO
(2d, 2p)/CGCST
H39
14.15
(s, 1H, Ar OH)
15.22
15.69
15.68
H40
9.37
(s, 1H, N=CH)
9.34
9.56
9.56
H41, H42, H43, H44
8.04–8.48
(9H, Ar CH, Pyrene)
8.32–9.03
8.46–9.46
8.45–9.46
H45, H46, H47, H48
H49
H31
8.50
(d, 1H, Ar CH)
8.50
8.77
8.77
H32
7.16
(d, 1H, Ar CH)
7.34
7.70
7.70
H33
8.66
(s, 1H, Ar CH)
8.66
8.99
8.99
H34, H35
4.32–4.38
(s, 2H, O–CH2)
4.27–4.32
4.75–4.82
4.74–4.81
H36, H37, H38
1.36–1.40
(T, 3H, C–CH3)
1.31–1.46
1.60–1.89
1.60–1.89Table 3
Comparison of B3LYP/6-311++G(2d, 2p) calculated and experimental values [1]* of 13C chemical shift (ppm) relative to the TMS for the title compound.
Atom
Experimental
6-311++G
6-311++G
6-311++G
(2d, 2p)/GIAO
(2d, 2p)/CGST
C15–C30
117.52–141.50
(16C, Ar C, pyrene)
115.60–148.50
118.77–167.66
118.76–167.66
C1–C6
115.67–165.12
(6C, Ar C, substituted benzene)
121.53–175.80
120.60–176.80
120.59–176.80
C7
165.88
(1C, Ar C=O)
180.00
179.0
179.07
C13
162.81
(1C, Ar C=N)
169.94
167.66
167.66
C10
60.98
(1C, OCH2)
60.56
68.66
68.66
C11
14.44
(1C, CH3)
13.48
13.51
13.50


### 4.3. Frontier Molecular Orbitals

Analysis of the HOMO-LUMO band gap helps us in understanding many molecular properties of a molecule like chemical reactivity, UV-Vis spectra, and stability of the molecule [16] along with optical and electrical properties. Chemical reactivity of a molecule can be determined from the HOMO-LUMO band gap. A small band gap implies low kinetic stability of the molecule. HOMO-LUMO separation is a result of significant degree of intermolecular charge transfer from the electron donor groups to the electron acceptor groups through π conjugated paths. Energy gap between HOMO and LUMO has also been used to prove the bioactivity from intramolecular charge transfer (ICT). We have reported the HOMO-LUMO analysis of the title compound using DFT/B3LYP/6-311++G(2d, 2p) level of theory [17]. In our analysis we found that the title compound has a total of 986 orbitals out of which 103 are occupied and the remaining 883 are virtual orbitals. The orbitals numbered as 103 and 104 account for HOMO and LUMO orbitals. The HOMO-LUMO energies of the title compound have also been calculated using ab initio calculations and are found to be −5.63 electron volts and −2.50 electron volts, respectively. The HOMO-LUMO for the title compound has been shown in Figure 4 and the gap is found to be 3.13 electron volts. The HOMO LUMO distribution is mostly localized on the rings which show that they are π type orbitals. HOMO(103)→LUMO(104) transition implies an ED transfer between rings (π→π*) transition. From this value of band gap we can predict that the title compound can be used for organic solar cell applications, title compound has high kinetic susceptibility and low chemical reactivity. Using HOMO and LUMO energies along with equations as ε=(I+A)/2 which is electronegativity, β=(I-A)/2 as chemical hardness with δ=1/2β as chemical softness has been calculated for the title compound. The terms I and A are equivalent to I=-EHOMO and A=-ELUMO and are referred to as ionization potential and electron affinity, respectively. In addition to HOMO/LUMO energies the HOMO−1/LUMO+1 energies of the title compound have been calculated using B3LYP/6-311++G(2d, 2p) level of theory and are found to be −5.61 eV and −2.41 eV, respectively. Electron donating and electron withdrawing ability of the title compound are expresses in terms of ε,β, and δ and come out to be 4.065, 1.565, and 0.3194 [18].Figure 4
HOMO/LUMO and HOMO−1/LUMO+1 energies of the title compound calculated at B3LYP level of theory using 6-311++G(2d, 2p) basis set.


### 4.4. MEP Surface Mapping

We have reported and plotted the MEP surface mapping, alpha density, and total density of the title compound using Gaussian 09 program. The molecular electrostatic potential surface along with Alpha density and total density for the title compound is represented in Figure5.Figure 5
MEP, alpha density, and total density of the title compound using Gaussian 09 package.MEP surface mapping is useful in understanding hydrogen bonding interactions as well as sites for electrophilic and nucleophilic attacks [19, 20]. The MEP surface provides us with net electrostatic effect caused due to total charge distribution. It can be considered as a fruitful quantity to understand the various molecular properties like hydrogen bonding and reactivity. It also provides a useful tool to know the relative polarity of the molecule [21]. Portion of the molecule which has –ve electrostatic potential will be susceptible to electrophilic attack. The surface is color coded as per the electrostatic potential (red is more electron rich area and blue is more electron poor area.). The total electron density plot of the title compound shows a uniform distribution. The order in the increase of the electrostatic potential as per color code will follow as red < orange < yellow < green < blue [22]. At last we conclude that the investigated molecule has several sites for electrophilic as well as nucleophilic attacks as shown in MEP surface mapping.


### 4.5. UV-Vis Studies and Electronic Properties

To find the electronic absorption spectrum including singlet and triplet states of the title compound the calculations were performed on fully optimized ground state geometry using DFT/B3LYP/6-31++G(2d, 2p) level of theory. THF is used as a solvent to simulate the electronic absorption. Figure6 represents the computed electronic spectra of the title compound. The electronic spectra are recorded within a range of 200 nm–800 nm. Using TDDFT theory the oscillator strength along with excitation energy for the triplet and the singlet states has also been calculated. The different values for excitation energy along with oscillator strength as well as CI expansion coefficients are listed in Table 4. For the title compound the maximum absorption value obtained using TD-DFT/B3LYP/6-311++G(2d, 2p) basis set are 485 nm, 332 nm, and 285 nm, respectively, with THF as solvent in CPCM model. Corresponding experimental values as reported are 383 nm and 258 nm, respectively. The calculated band at 485 nm is intense and accounts for a π→π* type of transition. λmax⁡ absorption band in the calculated spectrum indicates a HOMO(103)→LUMO(104) transition and is close to experimentally calculated values.Table 4
Calculated electronic absorption spectrum of (ethyl 4 hydroxy-3-((E)-(pyren-1-ylimino) methyl) benzoate) using TD DFT/B3LYP/6-311++G(2d, 2p), with experimentally reported values by other authors in brackets.
Excited state (triplet/singlet)
CI expansion coefficient
Energy (eV)
Wavelength calc. (nm)
Oscillator Strength (f)
1(T)
0.64282
1.8590
666.95
0.0000
103→104
−0.20390
103→105
−0.11486
103→106
2(T)
0.14567
2.6252
472.28
0.0000
99→104
−0.13249
100→104
−0.14414
101→104
−0.10275
101→105
−0.24936
102→104
0.17216
103→104
0.46822
103→105
−0.28107
103→106
0.69539
3(S)
0.69539
2.7450
451.67
0.7677
103→104
4(T)
0.13579
3.1085
398.86
0.0000
98→104
0.37034
101→104
0.24413
101→105
0.26932
102→104
0.17397
102→105
0.13812
103→104
0.12732
103→105
−0.30215
103→106
−0.15823
103→107
5(T)
−0.25829
3.2510
381.37 (383)
0.0000
101→104
0.54783
102→104
−0.16061
102→105
0.17231
103→105
0.18500
103→107
6(T)
0.12403
3.3508
370.01
0.0000
99→104
−0.18914
100→104
0.23302
101→104
0.10005
101→105
0.58730
103→107
7(S)
0.46263
3.4071
363.90
0.1405
102→104
0.42672
103→105
−0.18292
103→106
−0.22746
103→107
8(T)
0.38274
3.4113
363.45
0.0000
101→104
−0.15712
101→105
−0.28172
101→106
−0.18264
102→106
0.20011
103→105
0.29507
103→106
−0.12290
103→107
9(T)
−0.31383
3.4452
359.88
0.0000
99→104
0.12754
99→105
−0.18356
100→104
0.15473
100→105
−0.10501
100→106
0.10458
103→105
0.10831
103→106
0.48610
103→108
10(T)
0.26533
3.4968
354.56
0.0000
98→104
−0.17532
99→104
0.14537
99→106
0.25397
100→104
0.14670
101→106
−0.13584
102→104
0.14197
102→105
0.10470
103→104
0.26216
103→105
0.28660
103→106
0.15214
103→107
11(S)
0.28917
3.5463
349.62
0.0491
101→104
−0.13634
102→104
0.44769
103→105
0.37599
103→106
0.20752
103→107
12(S)
0.30776
3.6873
336.24
0.1203
102→104
0.10328
102→107
−0.23091
103→105
0.48945
103→106
0.24268
103→107
13(T)
0.13526
3.6887
336.12
0.0000
99→104
−0.17258
100→104
0.28909
101→105
0.14313
101→106
−0.13298
101→107
−0.14420
102→105
0.31031
102→106
0.21164
102→107
0.19945
103→105
0.22837
103→106
−0.12402
103→107
14(T)
0.44193
3.7249
332.85
0.0000
98→104
−0.13986
99→105
−0.25100
101→106
−0.21945
102→105
0.22073
102→107
−0.14380
103→109
15(S)
0.54944
3.7645
329.35
0.0736
101→104
0.23402
102→104
−0.19623
103→105
−0.22900
103→106
0.18853
103→107
16(S)
−0.28250
3.9579
313.25
0.1484
101→104
0.39900
102→104
0.18195
102→105
0.46966
103→107
17(S)
−0.11671
4.1055
301.99
0.0048
96→104
−0.24326
98→104
0.12165
99→104
0.57103
100→104
−0.11945
103→107
0.22342
103→108
18(S)
0.11882
4.1535
298.15
0.0127
98→104
−0.21315
100→104
0.64522
103→108
19(S)
0.15321
4.2776
289.84
0.0049
96→104
0.45970
98→104
0.41273
99→104
0.19557
100→104
20(S)
−0.30075
4.3829
282.88 (238)
0.3427
98→104
0.41155
99→104
−0.21058
100→104
0.25420
102→105
−0.28124
102→106Figure 6
UV-Vis spectrum of (ethyl 4 hydroxy-3-((E)-(pyren-1-ylimino)methyl)benzoate).


### 4.6. Vibrational Spectra

In the present study we have reported the molecular vibrations of the title compound by means of FTIR spectroscopy. Our title compound is asymmetric top with C1-symmetry and is characterized by 141 normal modes of vibration. We have used DFT/B3LYP/6-311++G(2d, 2p) [23] method to investigate the normal modes of vibration of our title compound. The main reason for selecting this computational scheme is that it reproduces experimental frequencies with high accuracy and the same can be predicted from the comparison of the calculated values with the experimental ones. The calculated and experimental FTIR spectra of the title compound are shown in Figure 6. On comparison we found that the calculated values using the above method are found to be in close agreement with the experimental values. Calculated C–H stretching vibrations of aromatic rings appeared in the wavenumber range 2800–3200 cm−1. The same has been confirmed with the experimental IR where the wavenumber range for aromatic rings ranges from 3000 to 3200 cm−1. The bands observed in the wavenumber range from 3250 to 2850 cm−1 in the calculated IR spectra of the title compound are assigned to the alkyl C–H stretching vibrations and the same is confirmed with the experimental values. C=O (ester) stretching vibrations are predicted at 1649 cm−1 while for the same functional group experimental values are at 1711 cm−1. C=N (Schiff base) stretching vibrations are predicted at 1611 cm−1, while experimental values are at 1610 cm−1. We have also analyzed and reported our modes of vibrations in terms of PED. PED analysis is done by using VEDA 4 program [24]. This program generally uses the Gaussian output file in formatted checkpoint form as its input files for PED analysis. These input files contain information about orientation of coordinates, force constants (F-matrix), and frequencies with atom displacement matrix. The information on F-matrix must start form the line “Force Constants in Cartesian coordinates” (Figure 7).The experimental (a)  [1]* and calculated (b) IR of the title compound.
(a)
(b)We have repeated our PED analysis few hundred times to achieve maximum value of PED contributions. In PED interpretation each fundamental normal mode coordinate is expressed in terms of internal mode coordinates which is a combination of stretchings, bendings, or torsions. This transformation basically results in the nondiagonality of the force constant matrix, which means that PED contributions of different modes are mutually related to each other by nondiagonal terms. Further we explain how this procedure works as a normal mode coordinate is replaced by an internal set of coordinates and PEDs are calculated. A parameter EPm is used to express the maximum PEDs and is basically considered as optimization of the PED analysis. If our title compound consists of a large number of modes, then it will result in an increase of optimization time. Theoretically calculated and experimental wavenumbers (available) are summarized in Table5. Detailed vibrational assignments, IR intensities, and computed wavenumbers along with the percentage of PED are given in Table 5. The spectra were analyzed in terms of the PED contributions by using the VEDA program.Table 5
Vibrational wavenumbers obtained for the title compound at B3LYP/6-311++G (2d, 2p) (Harmonic frequency (cm−1), IRint⁡ (cm−1)).
Experimental wavenumbers (cm−1)
Calculated wavenumbers (cm−1)
IR
int
⁡ (cm−1)
Raman (cm−1)
PED
Interpretation
3224.31
4.48
183.79
s11 93
υ
s (CH2), ring 1
3212.1
9.19
87.51
s13 94
υ
s (CH2), ring 4
3200
3205.53
2.7
72.41
s3 94
υ
as (CH2), ring 1
3191.45
60.42
530.75
s19 97
υ
s (CH3), ring 5
3189.28
27.8
114.52
s14 92
υ
s (CH2), ring 4
3183.94
1.57
36.38
s4 99
υ
s (CH), ring 1
3181
3181.15
51.58
278.89
s18 96
υ
s (CH2), ring 3
3171.65
24.78
229.97
s12 −13 s15 −83
υ
as (CH2), ring 5 + υs (CH), ring 4
3167.97
2.75
45.05
s12 78 s15 −15
υ
as (CH2), ring 4 + υs (CH2), ring 5
3167.24
11.88
60.89
s7 92
υ
as (CH2), ring 2
3161.69
0.24
47.53
s17 93
υ
as (CH3), ring 5
3158.71
1.74
40.37
s16 93
υ
as (CH2), ring 3
3119.2
48.59
16.84
s5 −13 s6 −10 s8 −17 s10 60
Not defined
3099.91
38.21
156.66
s6 −81
υ
as (CAH2)
3090
3090.57
0.93
95.26
S8 78 s10 −12
υ
as (CAH2)+ υs (CH2)
3059.21
20.49
88.61
s2 99
υ
s (CAH)
3052.38
15.95
154.12
s9 96
υ
s (CAH2)
3029.99
26.36
191.4
s5 76 s10 21
υ
s (CAH3)
2894.86
785.16
225.28
s1 96
υ
s (CAO)
1675.14
219.1
561.69
s26 −60
υ
s (CAO)
1711
1667.79
12.27
1522.05
s39 42
υ
s (C–C), ring 3, 4, 5
1648.5
371.86
211.55
s20 32 s23 −10
υ
s (CAO) + υs (C–C), ring 1, 4
1643.33
51.26
229.63
s20 −16 s23 −28
υ
s (CAO) + υs (C–C), ring 1, 4
1638.23
39.05
1129.96
s23 −16 s28 −22
υ
as (C–C), ring 3 + υas (C–C), ring 4
1629.61
22.25
3026.04
s21 11 s28 −23
υ
s (C–C), ring 1 + υas (C–C), ring 5
1622.07
16.12
824.95
s27 13 s81 11
υ
s (C–C), ring 4 + βCCC, ring 5
1610
1610.7
78.32
8784.86
s35 27
υ
s (CAN)
1583.63
8.54
225.08
s36 21 s39 −10 s60 11
υ
s (C–C), ring 2 + υas (C–C), ring 3 + βHCC, ring 3
1554.36
6.42
3.52
s62 70 s101 15
βHCC + τHCOC, (OCA)
1546.99
13.7
1548.31
s33 16 s68 −24
υ
s (C–C), ring 3 + βHCC, ring 2
1539.54
8.07
29.88
s61 70 s62 −10 s103 10
βHCH,0020(HCA) + βHCH, (HCA) + τHCOC, (OCA)
1526.21
9.1
23.7
s59 73 s100 −12
βHCH, (HCA) + τHCOC, (OCA)
1524.23
37.79
260.32
s25 12 s72 −10
υ
s (C=C), ring 5 + βHCH, ring 1
1518.08
71.68
2628.38
s25 11 s55 −14 s56 −10
υ
s (C=C), ring 2 + βHCC, ring 1
1495.75
21.77
369.81
s67 −25
βHCC, ring 3
1493.07
89.53
2975.2
s35 −13 s54 17
υ
s (CAN) + βHOC
1476.41
4.86
4.47
s60 22
βHOC
1465.71
3.62
246.14
s71 −65
βHCC, ring 5
1457.66
12.6
15.74
s63 84
βHCC, (HCA)
1451.13
6.85
16.4
s54 −11
βHOC, (OCA)
1444.01
6.01
106.44
s29 −15 s69 10
υ
s (C–C), ring 5 + βHCC, ring 3
1422.52
3.56
1171.11
s22 34
υ
s (C=C), ring 2
1418.96
8.01
160.33
s62 11 s101 67
βHCH, (HCA) + τHCOC, (OCA)
1407.13
11.57
189.62
s31 −23 s64 −17
υ
as (C–C), ring 5 + βHCN, (NCA)
1387.02
4.94
692.54
s31 −11 s64 31
υ
as (C–C), ring 5 + βHCN, (NCA)
1371.3
53.01
744.64
s24 −51 s42 13
υ
as (C–C), ring 1 + υs (C–C), ring 5
1365.37
3.17
20.73
s85 10
βCCC, ring 4
1347.53
8.32
30.53
s37 −41 s66 −10
υ
as (C=C), ring 2 + βHCC, ring 4
1322.41
32.6
186.95
s56 −45
βHCC, ring 1
1301.85
0.32
18.48
s58 76
βHCC, (CAH)
1293.46
1.16
19.8
s33 12 s60 10 s68 21
υ
as (C–C), ring 3 + βHCC, ring 4 + βHCC, ring 5
1290.84
115.58
764.31
s30 58
υ
s (CO), (CAO)
1284.22
2.96
455.48
s41 20 s69 −17
υ
s (C–C), ring 5 + βHCC, ring 5
1264.63
151.27
24.03
s26 −16 s57 −14
υ
as (C–C), ring 5 + βHCC, ring 1
1263.15
62.22
3895.41
s41 −11 s44 −11
+υas (C–C), ring 1 + υas (C–C), ring 5
1252.17
107.36
376.98
Not defined
1231.74
194.37
485.07
s32 −10 s72 21
υ
as (C–C), ring 2 + βHCC, ring 5
1223.49
154.6
440.05
s70 −52
βHCC, ring 2
1211.31
266.52
575.9
s70 −13
βHCC, ring 2
1196.58
52.39
47.76
s25 17 s66 40
υ
s (C=C), ring 4 + βHCC, ring 5
1190.05
0.98
29.65
s39 14s65 49
υ
s (C=C), ring 3 + βHCC, ring 3
1188.46
5.77
4.66
s58 −14 s100 54
βHCC (CAH) + τHCOC, (OCA)
1163.11
62.3
4.06
s29 25s57 55
υ
s (C=C), ring 1 + βHCC, ring 1
1147.16
3.05
19.94
s48 22 s61 −18 s94 −12 s103 −32
βHCH (CAH) + βCCO (CAO) + τHCCO (OCA)
1143.32
0.51
14.59
s77 32
βCCC, ring 4
1132.55
18.83
225.65
s69 11
βHCC, ring 5
1118.58
268.59
4.61
s46 −31 s55 15
υ
as (C=C), ring 1 + βHCC, ring 1
1085.93
16.59
30.98
s27 14 s34 22
υ
s (C=C), ring 3 + υs (C=C), ring 5
1039.71
88.12
4.02
s47 72
υ
as (C=C), (CAH)
1037.69
2.7
6.89
s102 −80
τHCCC, ring 4
1015.71
1
19.59
s112 −52
τHCCC, ring 5
1014.43
16.39
160.22
s99 −66
τHCNC, (CAN)
1005.48
0.18
0.64
s113 61
τHCCC, ring 3
1004.51
5.05
79.88
s106 74
τHCCC, ring 1
995.67
6.4
4.17
s32 10 s40 −12
υ
s (C–C), ring 2 + υas (C=C), ring 3
982.59
1.21
30.45
s109 66
τHCCC, ring 2
966.87
5.99
189.31
s97 38
τHCCC, ring 1
964.36
22.39
3.01
s97 44
τHCCC, ring 1
957.27
80.57
1.93
s96 75
τHOCC (CAO)
938.59
1.65
4.09
s110 72
τHCCC, ring 5
925.25
33.74
166.09
s44 −11 s79 −27
υ
as (CAN) + βCCC, ring 4
881.43
111.2
18.99
s108 −60
τHCCC, ring 2
876.59
42.03
10.19
s48 −12 s107 25
υ
as (C–C), ring 1 + τHCCC, ring 4
867.61
38.53
2.37
s98 60
τHCCC, ring 1
866.7
25.46
2.94
s48 −16 s98 −21 s107 −12 s108 −14
Not defined
846.41
10.78
2.34
s50 −54
βCCC, ring 4
833.53
3.4
6.97
s107 14 s111 31
τHCCC, ring 1 + τHCCC, ring 3
830.77
0.38
2.5
s104 70
τHCCO, (CAO)
828.69
9.21
66.05
s111 21
τHCCC, ring 2
815.14
3.69
7.4
s128 −18
τCCCC, ring 5
804.43
1.77
4.67
s73 −27
βOCO, (CAO)
793.29
1.08
59.46
s43 20 s82 18
υ
s (C–C), ring 1 + βCCC, ring 4
778.97
8.82
4.11
s114 67
τHCCC, ring 5
764.69
5.88
9.65
s82 17
βCCC, ring 1
760.34
19.23
0.69
s136 −51
ϕCCCC, ring 1
741.78
17.23
0.25
s107 −12 s111 11 s116 −11
τHCCC, ring 1 + τHCCC, ring 4 + τCCCC, ring 5
724.92
6.87
6.4
s141 55
ϕOCOC, (CAO)
714.44
0.19
18.14
s28 −11 s49 16
υ
s (C–C), ring 3 + βCCC, ring 4
702.64
8.92
32.91
s120 −15 s138 −10 s140 −24
τCCCC, ring 1 + ϕCCCC, ring 2 + ϕCCCC, ring 3
676.97
30.47
11.99
s41 11 s93 14
υ
s (C–C), ring 1 + βCCO, (CAO)
651.45
14.72
11.48
s51 −35
βCCC, ring 1
640.97
13.61
40.41
s126 12 s129 −11
τCCNC, ring 1 + τCCCC, ring 1
622.1
2.3
28.46
s38 −13 s80 17
υ
s (C–C), ring 3 + βCCN, (CAN)
578.44
0.11
9.98
s41 10 s49 10
υ
s (C–C), ring 3 + βCCC, ring 5
568.57
2.75
12.66
s121 −11 s122 −12 s124 −11s139 15
Not defined
559.84
0.71
13.11
s122 23 s124 10 s134 19
τCCCC, ring 1 + τCCCC, ring 3 + ϕCCCC, ring 5
546.17
11.74
2.14
Not defined
537.81
3.67
6.23
s52 24
βCCO, (CAO)
530.02
1.06
12.8
s117 24 s139 13
τCCCN, (CAN) + ϕCCCC, ring 3
521.45
3.05
74.21
s125 22 s127 14
τCCCC, ring 3 + τCCNC, (CAN)
512.46
0.83
1.44
s88 23
βCCC, ring 3
497.39
3.19
11.62
s76 −14 s83 11 s85 −15
βCCC, ring 3 + βCCN (CAN) + βCCC, ring 5
483.98
2.27
2.37
s123 −24 s135 24
τCCCC, ring 1 + ϕCCCC, ring 2
460.5
1.9
6.03
s87 20
βCCC, ring 4
444.53
1.19
3.6
s124 10
τCCCC, ring 1
432.84
0.68
21.66
s91 41
βCCO (CAO)
415.6
2.46
89.07
s22 −11 s90 −14
υ
as (C–C), ring 4 + βCCC, ring 3
386.89
0.5
1.35
s86 −10
βCCC, ring 2
372.32
11.47
1.34
s75 −16s94 56
βCOC, (CAO) + βCCO, (CAO)
355.13
1.38
4.26
s123 19 s135 10
τCCCC, ring 3 + ϕCCCC, ring 5
346.91
3.4
73.7
s115 −11
τNCCC, (CAN)
311.17
4.64
20.43
s45 −15 s95 31
υ
as (C–C), ring 4 + βCOC, (CAO)
289.37
5.1
68.61
s115 24
τNCCC, (CAN)
273
0.46
2.42
s105 −10 s121 17 s139 15
τCCCO, (CAO) + τCCCC, ring 3 + ϕCCCC, ring 5
267.89
0.58
7.14
s75 13
βCOC, (CAO)
252.25
1.23
10.57
s103 12s105 55
τCCCO, (CAO)
241.04
2.81
9.87
s75 12
βCOC, (CAO)
223.33
8.26
10.27
s138 −43
ϕCCCC, ring 4
186.81
5.98
7.28
s89 12s116 −17
βCCC, (CA) + τCCCN, (CAN)
171.6
0.34
10.17
Not defined
152.06
7.4
9.77
s118 24 s133 37
τCCCC, ring 1 + ϕCOCC, (CAO)
134.24
3.04
26.07
s75 −10
βCOC (CAO)
122.64
0.08
11.46
s119 15 s129 −11
τCCCN, (CAN) + τCCNC, (CAN)
100.65
1.28
6.44
s119 10 s127 14
τCCCN, (CAN) + τCCNC, (CAN)
92.61
0.67
7.41
s118 11 s131 −15 s133 −20 s134 13
τCOCC, (CAO)
79.9
0.64
3.96
s92 23 s131 12
βCCC, ring 4 + τCOCC, (CAO)
59.62
0.88
2.9
s130 −16 s131 −37
τCOCC, (CAO)
39.59
0.12
2.58
s130 48 s131 13 s132 −11
τCOCC, (CAO)
31.93
0.14
5.25
s74 −42
βCNC (CAN)
21.6
0.27
6.59
s126 12 s132 47
τCCNC, (CAN) + τCOCC, (CAO)
16.34
0.3
8.44
s126 18 s132 −22 s135 12
τCCNC, (CAN) + τCOCC, (CAO) + ϕCCCC, ring 3
υ, β, τ, and ϕ denote the stretching, bending, torsion, and out (ϕ ABCD means the angle between the AD vector and the BCD plane) modes. Indices notation: s: symmetric; as: asymmetric; A: aliphatic; ring 1: C1-C2-C3-C4-C5-C6; ring 2: C15-C16-C17-C18-C19-C20; ring 3: C21-C22-C23-C24-C16-C17; ring 4: C17-C18-C24-C25-C26-C27; ring 5: C23-C24-C25-C28-C29-C30.


#### 4.6.1. Ring, C=O and C=N Vibrations

The C–H stretching vibrations in the range 2800–3200 cm−1 are for aromatic compounds. From the PED analysis we found that C–H stretching vibrations for ring 1 are assigned at 3183 cm−1. This mode is very pure mode as its PED analysis is about 99%. The values observed in the range (3158–3224) cm−1 are assigned to the stretching vibrations of methyl hydrogen’s while their experimentally obtained counterparts are at 3200 cm−1 and 3118 cm−1, respectively. The percentage of PED calculated for these modes by VEDA 4 program varies from 92 to 99% indicating that they are pure modes. C–N modes of vibrations are assigned on the basis of PED calculations. In the PED analysis we found that C–N modes of vibrations are at 1407 and 1387 cm−1 respectively, however these modes are not pure modes and are mixed with C–C stretching modes, while experimentally observed value is at 1611 cm−1. On the basis of PED analysis the wavenumbers at 1648, 1643, 1675, 1554, and 1526 cm−1 are assigned to C=O stretching modes, however again these modes are not pure modes and are mixed with other modes of vibrations. Experimentally obtained values for C=O stretching modes is at 1649 cm−1. The PED analysis for various modes of the title compound along with their percentage values are summarized in Table 5.


### 4.7. NBO Analysis

In order to understand the hyper conjugation as well as delocalization of the title compound we have investigated the natural bond orbital analysis of the title compound using NBO 3.1 program implemented in Gaussian 09 package [25]. We have used DFT/B3LYP/6-311++G(2d, 2p) level of theory in order to understand different kind of interactions between the filled and the vacant orbitals. We can investigate both intra- and intermolecular interactions using NBO analysis. In addition to this NBO analysis is also useful for understanding charge transfer conjugative interactions in different compounds. Using DFT/B3LYP/6-311++G(2d, 2p) level of theory the second-order perturbation theory analysis of Fock matrix in NBO basis [26] for title compound is listed in Table 6. For each donor (i) and acceptor (j) the stabilization energy E(2) associated with the delocalization i→j is determined as
(1)E(2)=ΔEijqi(Fij)2(Ej-Ei).
Large E(2) value shows the intensive interaction between electron-donors and electron-acceptors groups and greater extent of conjugation of the whole system. The possible intensive interactions are also listed in Table 6. The second-order perturbation theory analysis of Fock matrix in NBO basis shows strong intramolecular hyper conjugative interactions of π electrons. From Table 6 we can see that the intramolecular hyper conjugative interactions are formed by the orbital overlap between oxygen, nitrogen, and carbon-carbon bond orbitals. This orbital overlapping is responsible for ICT causing stabilization of the system under study. From the analysis of Table 6 we found that the strong intramolecular hyper conjugative interaction is of C7–O9 from n2(O8)→π* (C7–O9)which increases ED (0.10070 e) that weakens the respective bonds leading to stabilization of 32.78 kcal mol−1. Similarly another strong intramolecular hyper conjugative interaction of C7–O8 from n2(O9)→π*(C7–O8) increases ED (0.28565 e) that weakens the respective bonds leading to stabilization of 46.67 kcal mol−1. We have also found another strong intramolecular hyper conjugative interaction of C21–C22 from n1(C23)→π* (C21–C22) which increases ED (0.18831 e) that also weakens the respective bonds leading to stabilization of 46.88 kcal mol−1. We predicted one more strong intramolecular hyper conjugative interaction of C21–C22 from n1(C23)→π*(C21–C22) which increases ED (0.18831 e) that weakens the respective bonds leading to stabilization of 46.88 kcal mol−1, as well as strong intramolecular hyper conjugative interaction of C24–C25 from n1(C23)→π*(C24–C25) which increases ED (0.46625 e) that weakens the respective bonds leading to stabilization of 71.49 kcal mol−1. These interactions are observed as an increase in electron density (ED) in C–C antibonding orbitals that weakens the respective bonds.Table 6
Second-order perturbation theory analysis of Fock matrix in NBO basis.
Donor (i)
Type
ED/e
Acceptor (j)
Type
ED/e
E(2)a (kcalmol−1)
E
(
j
)
-
E
(
i
)
b (a.u)
F
(
i
,
j
)
c
(a.u)
C1–C2
π
1.68952
C3–C4
π
*
0.45595
25.08
0.26
0.075
C1–C2
π
1.68952
C5–C6
π
*
0.35531
15.88
0.28
0.060
C1–C6
σ
1.63511
C9–C10
σ
*
0.34194
4.65
1.25
0.068
C3–C4
π
1.55498
C1–C2
π
*
0.27464
13.45
0.29
0.058
C3–C4
π
1.55498
C5–C6
π
*
0.35531
25.35
0.28
0.077
C3–C4
π
1.55498
C13–N14
π
*
0.21940
23.30
0.25
0.072
C5–C6
π
1.65905
C1–C2
π
*
0.27464
22.39
0.28
0.072
C5–C6
π
1.65905
C1–C2
π
*
0.45595
15.42
0.26
0.059
C5–C6
π
1.65905
C7–O8
π
*
0.28565
27.55
0.24
0.074
C13–C14
π
1.91336
C3–C4
π
*
0.45595
6.89
0.94
0.023
C13–C14
π
1.91336
C15–C16
π
*
0.44368
9.43
0.37
0.058
C15–C16
π
1.96604
C13–N14
π
*
0.21940
11.21
0.24
0.049
C15–C16
π
1.96604
C17–C18
π
*
0.46912
19.03
0.28
0.066
C15–C16
π
1.96604
C19–C20
π
*
0.32861
19.83
0.27
0.067
C15–C16
π
1.96604
C21–C22
π
*
0.18831
15.74
0.29
0.064
C17–C18
π
1.52506
C15–C16
π
*
0.44368
20.29
0.26
0.066
C17–C18
π
1.52506
C19–C20
π
*
0.32861
19.87
0.26
0.066
C17–C18
π
1.52506
C24–C25
π
*
0.46625
19.54
0.27
0.065
C17–C18
π
1.52506
C26–C27
π
*
0.19336
14.49
0.28
0.061
C19–C20
π
1.68814
C15–C16
π
*
0.44368
19.18
0.28
0.068
C19–C20
π
1.68814
C17–C18
π
*
0.46912
17.64
0.29
0.066
C21–C22
π
1.79067
C15–C16
π
*
0.44368
17.23
0.28
0.066
C24–C25
π
1.53004
C17–C18
π
*
0.46912
20.01
0.27
0.065
C24–C25
π
1.53004
C26–C27
π
*
0.19336
14.62
0.27
0.061
C26–C27
π
1.79745
C17–C18
π
*
0.46912
14.32
0.29
0.062
C26–C27
π
1.79745
C24–C25
π
*
0.46625
14.02
0.30
0.062
LP(2)O8
n
1.86096
C6–C7
σ
*
0.05894
15.13
0.69
0.093
LP(2)O8
n
1.86096
C7–O9
σ
*
0.10070
32.78
0.57
0.123
LP(1)O9
n
1.96939
C7–O8
σ
*
0.01769
6.52
1.08
0.075
LP(2)O9
n
1.80240
C7–O8
π
*
0.28565
46.67
0.30
0.108
LP(2)O9
n
1.80240
C7–O8
π
*
0.28565
46.67
0.30
0.108
LP(1)O12
n
1.97419
C3–C4
σ
0.04045
7.37
1.05
0.079
LP(2)O12
n
1.79696
C3–C4
π
*
0.45595
37.12
0.31
0.102
LP(1)N14
n
1.84279
C3–C4
σ
*
0.03276
10.67
0.74
0.082
LP(1)C23
n
0.99827
C21–C22
π
*
0.18831
48.68
0.14
0.097
LP(1)C23
n
0.99827
C24–C25
π
*
0.46625
71.49
0.14
0.103
LP(1)C23
n
0.99827
C21–C22
π
*
0.33071
68.23
0.13
0.104
a
E(2) means stabilization energy.
bEnergy difference between the donor and acceptor NBO orbitals.
c
F
(
i
,
j
) is the Fock matrix element between i and j NBO orbitals.


## 4.1. Molecular Geometry

We have used the DFT/B3LYP/6-311++G(2d, 2p) level of theory available in Gaussian 09 program to investigate the ground state geometry of the title compound. The geometry is fully optimized with tight convergence criteria and the structure is local minima on the PES. On comparison with the experimentally obtained parameters one can conclude that our calculation is successful, as the difference between calculated and experimental bond lengths, bond angles is of few Å. Figure2 represents the stable conformation of the title compound using DFT calculations. The selected calculated bond lengths (R) and angles (Å) for the title compound along with their corresponding experimental values are listed in Table 1.Table 1
The selected calculated and experimental values [1]* for the stable conformation of the title compound.
Serial number
R (bond length/angstrom)
Calculated
Experimental
1
R (3, 12)
1.36
1.35
2
R (7, 8)
1.24
1.23
3
R (13, 14)
1.30
1.29
4
R (9, 7)
1.37
1.34
5
R (9, 10)
1.48
1.45
6
R (14, 15)
1.41
1.41
Serial number
A (angle/degrees)
Calculated
Experimental
1
A (13-14-15)
121.30
120.98
2
A (12-3-4)
121.10
120.37
3
A (8-7-6)
124.98
124.94
4
A (9-10-11)
106.83
106.84
5
A (7-9-10)
117.12
117.78
6
A (12-3-2)
118.82
118.86
7
A (8-7-9)
122.09
123.01
8
A (9-7-6)
112.92
112.95
R: Bond lengths (in Angstrom); A: Angles (in Degrees).Figure 2
Stable structure of new Schiff base using DFT approach with energy = −1282.65751536 au.Correlation between [14] the calculated and the experimental parameters of bond lengths and bond parameters for the title compound are shown in Figure 3. Bond length and bond angles correlation R2 values are 0.9802 and 0.9921, respectively.Correlation between the calculated and the experimental values of the (a) bond angles and (b) bond length for the stable conformation of the title compound.
(a)
(b)


## 4.2. Chemical Shifts

NMR spectroscopy is considered as a valuable tool for the structural and functional characterization of molecules.1H and 13C NMR chemical shifts of the title compound are investigated using DFT/B3LYP/6-311++G(2d, 2p) level of theory with GIAO (gauge-invariant atomic orbital) approach in DMSO. The calculated 1H and 13C NMR chemical shifts of the title compound together with the corresponding experimental values are shown in Tables 2 and 3 as values relative to tetramethylsilane. The 1H NMR spectra of the title compound in DMSO show a triplet peak in the range from 1.36 to 1.40 ppm for C–CH3 and quartet peak in the range from 4.32 to 4.38 ppm for O–CH2. Corresponding calculated values are in the range from 1.31 to 1.46 ppm and 4.27 to 4.32 ppm, respectively. Aromatic protons in pyrene appeared in the range from 8.04 to 8.48 ppm with calculated values ranging from 8.32 to 9.03 ppm. Aromatic protons in substituted benzene showed a singlet peak at 8.66 ppm and doublet at 8.50 ppm and 7.16 ppm. Corresponding calculated values are 8.66 ppm, 8.50 ppm, and 7.44 ppm, respectively. Proton of Schiff base shows a singlet peak at 9.37 ppm while calculated value is at 9.34 ppm. The 13C NMR spectra of the title compound in DMSO showed a peak at 14.44 ppm for C–CH3 (calculated value as 13.48 ppm), at 60.99 ppm for O–CH2 (calculated value as 60.56 ppm), at 165.88 ppm for C=O (calculated value as 180.00 ppm), and at 162.81 ppm for C=N (calculated value as 169.94 ppm). Aromatic carbons of pyrene and substituted benzene showed peaks in the range from 115.67 to 165.12 ppm while calculated values are in the range from 121.53 to 175.80 ppm. We have also reported the hydrogen and carbon NMR chemical shifts by IGAIM and CGST methods using B3LYP/6-311++G(2d, 2p) basis sets [15]. From the comparison table we can conclude that theoretical values for carbon and hydrogen NMR chemical shifts calculated by GIAO method are in close agreement as compared to other CGCST and IGAIM methods. Linear correlation coefficients (R2) for linear regression analysis of theoretical and experimental values of 1H and 13C NMR chemical shifts using GIAO method are found to be 0.9959 and 0.9958 respectively.Table 2
Comparison of DFT/B3LYP/6-311++G (2d, 2p) calculated and experimental values [1]* of 1H chemical shift (ppm) relative to the TMS for the title compound.
Atom
Experimental value
6311++G
6311++G
6-311++G
(2d, 2p)/GIAO
(2d, 2p)/CGCST
H39
14.15
(s, 1H, Ar OH)
15.22
15.69
15.68
H40
9.37
(s, 1H, N=CH)
9.34
9.56
9.56
H41, H42, H43, H44
8.04–8.48
(9H, Ar CH, Pyrene)
8.32–9.03
8.46–9.46
8.45–9.46
H45, H46, H47, H48
H49
H31
8.50
(d, 1H, Ar CH)
8.50
8.77
8.77
H32
7.16
(d, 1H, Ar CH)
7.34
7.70
7.70
H33
8.66
(s, 1H, Ar CH)
8.66
8.99
8.99
H34, H35
4.32–4.38
(s, 2H, O–CH2)
4.27–4.32
4.75–4.82
4.74–4.81
H36, H37, H38
1.36–1.40
(T, 3H, C–CH3)
1.31–1.46
1.60–1.89
1.60–1.89Table 3
Comparison of B3LYP/6-311++G(2d, 2p) calculated and experimental values [1]* of 13C chemical shift (ppm) relative to the TMS for the title compound.
Atom
Experimental
6-311++G
6-311++G
6-311++G
(2d, 2p)/GIAO
(2d, 2p)/CGST
C15–C30
117.52–141.50
(16C, Ar C, pyrene)
115.60–148.50
118.77–167.66
118.76–167.66
C1–C6
115.67–165.12
(6C, Ar C, substituted benzene)
121.53–175.80
120.60–176.80
120.59–176.80
C7
165.88
(1C, Ar C=O)
180.00
179.0
179.07
C13
162.81
(1C, Ar C=N)
169.94
167.66
167.66
C10
60.98
(1C, OCH2)
60.56
68.66
68.66
C11
14.44
(1C, CH3)
13.48
13.51
13.50


## 4.3. Frontier Molecular Orbitals

Analysis of the HOMO-LUMO band gap helps us in understanding many molecular properties of a molecule like chemical reactivity, UV-Vis spectra, and stability of the molecule [16] along with optical and electrical properties. Chemical reactivity of a molecule can be determined from the HOMO-LUMO band gap. A small band gap implies low kinetic stability of the molecule. HOMO-LUMO separation is a result of significant degree of intermolecular charge transfer from the electron donor groups to the electron acceptor groups through π conjugated paths. Energy gap between HOMO and LUMO has also been used to prove the bioactivity from intramolecular charge transfer (ICT). We have reported the HOMO-LUMO analysis of the title compound using DFT/B3LYP/6-311++G(2d, 2p) level of theory [17]. In our analysis we found that the title compound has a total of 986 orbitals out of which 103 are occupied and the remaining 883 are virtual orbitals. The orbitals numbered as 103 and 104 account for HOMO and LUMO orbitals. The HOMO-LUMO energies of the title compound have also been calculated using ab initio calculations and are found to be −5.63 electron volts and −2.50 electron volts, respectively. The HOMO-LUMO for the title compound has been shown in Figure 4 and the gap is found to be 3.13 electron volts. The HOMO LUMO distribution is mostly localized on the rings which show that they are π type orbitals. HOMO(103)→LUMO(104) transition implies an ED transfer between rings (π→π*) transition. From this value of band gap we can predict that the title compound can be used for organic solar cell applications, title compound has high kinetic susceptibility and low chemical reactivity. Using HOMO and LUMO energies along with equations as ε=(I+A)/2 which is electronegativity, β=(I-A)/2 as chemical hardness with δ=1/2β as chemical softness has been calculated for the title compound. The terms I and A are equivalent to I=-EHOMO and A=-ELUMO and are referred to as ionization potential and electron affinity, respectively. In addition to HOMO/LUMO energies the HOMO−1/LUMO+1 energies of the title compound have been calculated using B3LYP/6-311++G(2d, 2p) level of theory and are found to be −5.61 eV and −2.41 eV, respectively. Electron donating and electron withdrawing ability of the title compound are expresses in terms of ε,β, and δ and come out to be 4.065, 1.565, and 0.3194 [18].Figure 4
HOMO/LUMO and HOMO−1/LUMO+1 energies of the title compound calculated at B3LYP level of theory using 6-311++G(2d, 2p) basis set.


## 4.4. MEP Surface Mapping

We have reported and plotted the MEP surface mapping, alpha density, and total density of the title compound using Gaussian 09 program. The molecular electrostatic potential surface along with Alpha density and total density for the title compound is represented in Figure5.Figure 5
MEP, alpha density, and total density of the title compound using Gaussian 09 package.MEP surface mapping is useful in understanding hydrogen bonding interactions as well as sites for electrophilic and nucleophilic attacks [19, 20]. The MEP surface provides us with net electrostatic effect caused due to total charge distribution. It can be considered as a fruitful quantity to understand the various molecular properties like hydrogen bonding and reactivity. It also provides a useful tool to know the relative polarity of the molecule [21]. Portion of the molecule which has –ve electrostatic potential will be susceptible to electrophilic attack. The surface is color coded as per the electrostatic potential (red is more electron rich area and blue is more electron poor area.). The total electron density plot of the title compound shows a uniform distribution. The order in the increase of the electrostatic potential as per color code will follow as red < orange < yellow < green < blue [22]. At last we conclude that the investigated molecule has several sites for electrophilic as well as nucleophilic attacks as shown in MEP surface mapping.


## 4.5. UV-Vis Studies and Electronic Properties

To find the electronic absorption spectrum including singlet and triplet states of the title compound the calculations were performed on fully optimized ground state geometry using DFT/B3LYP/6-31++G(2d, 2p) level of theory. THF is used as a solvent to simulate the electronic absorption. Figure6 represents the computed electronic spectra of the title compound. The electronic spectra are recorded within a range of 200 nm–800 nm. Using TDDFT theory the oscillator strength along with excitation energy for the triplet and the singlet states has also been calculated. The different values for excitation energy along with oscillator strength as well as CI expansion coefficients are listed in Table 4. For the title compound the maximum absorption value obtained using TD-DFT/B3LYP/6-311++G(2d, 2p) basis set are 485 nm, 332 nm, and 285 nm, respectively, with THF as solvent in CPCM model. Corresponding experimental values as reported are 383 nm and 258 nm, respectively. The calculated band at 485 nm is intense and accounts for a π→π* type of transition. λmax⁡ absorption band in the calculated spectrum indicates a HOMO(103)→LUMO(104) transition and is close to experimentally calculated values.Table 4
Calculated electronic absorption spectrum of (ethyl 4 hydroxy-3-((E)-(pyren-1-ylimino) methyl) benzoate) using TD DFT/B3LYP/6-311++G(2d, 2p), with experimentally reported values by other authors in brackets.
Excited state (triplet/singlet)
CI expansion coefficient
Energy (eV)
Wavelength calc. (nm)
Oscillator Strength (f)
1(T)
0.64282
1.8590
666.95
0.0000
103→104
−0.20390
103→105
−0.11486
103→106
2(T)
0.14567
2.6252
472.28
0.0000
99→104
−0.13249
100→104
−0.14414
101→104
−0.10275
101→105
−0.24936
102→104
0.17216
103→104
0.46822
103→105
−0.28107
103→106
0.69539
3(S)
0.69539
2.7450
451.67
0.7677
103→104
4(T)
0.13579
3.1085
398.86
0.0000
98→104
0.37034
101→104
0.24413
101→105
0.26932
102→104
0.17397
102→105
0.13812
103→104
0.12732
103→105
−0.30215
103→106
−0.15823
103→107
5(T)
−0.25829
3.2510
381.37 (383)
0.0000
101→104
0.54783
102→104
−0.16061
102→105
0.17231
103→105
0.18500
103→107
6(T)
0.12403
3.3508
370.01
0.0000
99→104
−0.18914
100→104
0.23302
101→104
0.10005
101→105
0.58730
103→107
7(S)
0.46263
3.4071
363.90
0.1405
102→104
0.42672
103→105
−0.18292
103→106
−0.22746
103→107
8(T)
0.38274
3.4113
363.45
0.0000
101→104
−0.15712
101→105
−0.28172
101→106
−0.18264
102→106
0.20011
103→105
0.29507
103→106
−0.12290
103→107
9(T)
−0.31383
3.4452
359.88
0.0000
99→104
0.12754
99→105
−0.18356
100→104
0.15473
100→105
−0.10501
100→106
0.10458
103→105
0.10831
103→106
0.48610
103→108
10(T)
0.26533
3.4968
354.56
0.0000
98→104
−0.17532
99→104
0.14537
99→106
0.25397
100→104
0.14670
101→106
−0.13584
102→104
0.14197
102→105
0.10470
103→104
0.26216
103→105
0.28660
103→106
0.15214
103→107
11(S)
0.28917
3.5463
349.62
0.0491
101→104
−0.13634
102→104
0.44769
103→105
0.37599
103→106
0.20752
103→107
12(S)
0.30776
3.6873
336.24
0.1203
102→104
0.10328
102→107
−0.23091
103→105
0.48945
103→106
0.24268
103→107
13(T)
0.13526
3.6887
336.12
0.0000
99→104
−0.17258
100→104
0.28909
101→105
0.14313
101→106
−0.13298
101→107
−0.14420
102→105
0.31031
102→106
0.21164
102→107
0.19945
103→105
0.22837
103→106
−0.12402
103→107
14(T)
0.44193
3.7249
332.85
0.0000
98→104
−0.13986
99→105
−0.25100
101→106
−0.21945
102→105
0.22073
102→107
−0.14380
103→109
15(S)
0.54944
3.7645
329.35
0.0736
101→104
0.23402
102→104
−0.19623
103→105
−0.22900
103→106
0.18853
103→107
16(S)
−0.28250
3.9579
313.25
0.1484
101→104
0.39900
102→104
0.18195
102→105
0.46966
103→107
17(S)
−0.11671
4.1055
301.99
0.0048
96→104
−0.24326
98→104
0.12165
99→104
0.57103
100→104
−0.11945
103→107
0.22342
103→108
18(S)
0.11882
4.1535
298.15
0.0127
98→104
−0.21315
100→104
0.64522
103→108
19(S)
0.15321
4.2776
289.84
0.0049
96→104
0.45970
98→104
0.41273
99→104
0.19557
100→104
20(S)
−0.30075
4.3829
282.88 (238)
0.3427
98→104
0.41155
99→104
−0.21058
100→104
0.25420
102→105
−0.28124
102→106Figure 6
UV-Vis spectrum of (ethyl 4 hydroxy-3-((E)-(pyren-1-ylimino)methyl)benzoate).


## 4.6. Vibrational Spectra

In the present study we have reported the molecular vibrations of the title compound by means of FTIR spectroscopy. Our title compound is asymmetric top with C1-symmetry and is characterized by 141 normal modes of vibration. We have used DFT/B3LYP/6-311++G(2d, 2p) [23] method to investigate the normal modes of vibration of our title compound. The main reason for selecting this computational scheme is that it reproduces experimental frequencies with high accuracy and the same can be predicted from the comparison of the calculated values with the experimental ones. The calculated and experimental FTIR spectra of the title compound are shown in Figure 6. On comparison we found that the calculated values using the above method are found to be in close agreement with the experimental values. Calculated C–H stretching vibrations of aromatic rings appeared in the wavenumber range 2800–3200 cm−1. The same has been confirmed with the experimental IR where the wavenumber range for aromatic rings ranges from 3000 to 3200 cm−1. The bands observed in the wavenumber range from 3250 to 2850 cm−1 in the calculated IR spectra of the title compound are assigned to the alkyl C–H stretching vibrations and the same is confirmed with the experimental values. C=O (ester) stretching vibrations are predicted at 1649 cm−1 while for the same functional group experimental values are at 1711 cm−1. C=N (Schiff base) stretching vibrations are predicted at 1611 cm−1, while experimental values are at 1610 cm−1. We have also analyzed and reported our modes of vibrations in terms of PED. PED analysis is done by using VEDA 4 program [24]. This program generally uses the Gaussian output file in formatted checkpoint form as its input files for PED analysis. These input files contain information about orientation of coordinates, force constants (F-matrix), and frequencies with atom displacement matrix. The information on F-matrix must start form the line “Force Constants in Cartesian coordinates” (Figure 7).The experimental (a)  [1]* and calculated (b) IR of the title compound.
(a)
(b)We have repeated our PED analysis few hundred times to achieve maximum value of PED contributions. In PED interpretation each fundamental normal mode coordinate is expressed in terms of internal mode coordinates which is a combination of stretchings, bendings, or torsions. This transformation basically results in the nondiagonality of the force constant matrix, which means that PED contributions of different modes are mutually related to each other by nondiagonal terms. Further we explain how this procedure works as a normal mode coordinate is replaced by an internal set of coordinates and PEDs are calculated. A parameter EPm is used to express the maximum PEDs and is basically considered as optimization of the PED analysis. If our title compound consists of a large number of modes, then it will result in an increase of optimization time. Theoretically calculated and experimental wavenumbers (available) are summarized in Table5. Detailed vibrational assignments, IR intensities, and computed wavenumbers along with the percentage of PED are given in Table 5. The spectra were analyzed in terms of the PED contributions by using the VEDA program.Table 5
Vibrational wavenumbers obtained for the title compound at B3LYP/6-311++G (2d, 2p) (Harmonic frequency (cm−1), IRint⁡ (cm−1)).
Experimental wavenumbers (cm−1)
Calculated wavenumbers (cm−1)
IR
int
⁡ (cm−1)
Raman (cm−1)
PED
Interpretation
3224.31
4.48
183.79
s11 93
υ
s (CH2), ring 1
3212.1
9.19
87.51
s13 94
υ
s (CH2), ring 4
3200
3205.53
2.7
72.41
s3 94
υ
as (CH2), ring 1
3191.45
60.42
530.75
s19 97
υ
s (CH3), ring 5
3189.28
27.8
114.52
s14 92
υ
s (CH2), ring 4
3183.94
1.57
36.38
s4 99
υ
s (CH), ring 1
3181
3181.15
51.58
278.89
s18 96
υ
s (CH2), ring 3
3171.65
24.78
229.97
s12 −13 s15 −83
υ
as (CH2), ring 5 + υs (CH), ring 4
3167.97
2.75
45.05
s12 78 s15 −15
υ
as (CH2), ring 4 + υs (CH2), ring 5
3167.24
11.88
60.89
s7 92
υ
as (CH2), ring 2
3161.69
0.24
47.53
s17 93
υ
as (CH3), ring 5
3158.71
1.74
40.37
s16 93
υ
as (CH2), ring 3
3119.2
48.59
16.84
s5 −13 s6 −10 s8 −17 s10 60
Not defined
3099.91
38.21
156.66
s6 −81
υ
as (CAH2)
3090
3090.57
0.93
95.26
S8 78 s10 −12
υ
as (CAH2)+ υs (CH2)
3059.21
20.49
88.61
s2 99
υ
s (CAH)
3052.38
15.95
154.12
s9 96
υ
s (CAH2)
3029.99
26.36
191.4
s5 76 s10 21
υ
s (CAH3)
2894.86
785.16
225.28
s1 96
υ
s (CAO)
1675.14
219.1
561.69
s26 −60
υ
s (CAO)
1711
1667.79
12.27
1522.05
s39 42
υ
s (C–C), ring 3, 4, 5
1648.5
371.86
211.55
s20 32 s23 −10
υ
s (CAO) + υs (C–C), ring 1, 4
1643.33
51.26
229.63
s20 −16 s23 −28
υ
s (CAO) + υs (C–C), ring 1, 4
1638.23
39.05
1129.96
s23 −16 s28 −22
υ
as (C–C), ring 3 + υas (C–C), ring 4
1629.61
22.25
3026.04
s21 11 s28 −23
υ
s (C–C), ring 1 + υas (C–C), ring 5
1622.07
16.12
824.95
s27 13 s81 11
υ
s (C–C), ring 4 + βCCC, ring 5
1610
1610.7
78.32
8784.86
s35 27
υ
s (CAN)
1583.63
8.54
225.08
s36 21 s39 −10 s60 11
υ
s (C–C), ring 2 + υas (C–C), ring 3 + βHCC, ring 3
1554.36
6.42
3.52
s62 70 s101 15
βHCC + τHCOC, (OCA)
1546.99
13.7
1548.31
s33 16 s68 −24
υ
s (C–C), ring 3 + βHCC, ring 2
1539.54
8.07
29.88
s61 70 s62 −10 s103 10
βHCH,0020(HCA) + βHCH, (HCA) + τHCOC, (OCA)
1526.21
9.1
23.7
s59 73 s100 −12
βHCH, (HCA) + τHCOC, (OCA)
1524.23
37.79
260.32
s25 12 s72 −10
υ
s (C=C), ring 5 + βHCH, ring 1
1518.08
71.68
2628.38
s25 11 s55 −14 s56 −10
υ
s (C=C), ring 2 + βHCC, ring 1
1495.75
21.77
369.81
s67 −25
βHCC, ring 3
1493.07
89.53
2975.2
s35 −13 s54 17
υ
s (CAN) + βHOC
1476.41
4.86
4.47
s60 22
βHOC
1465.71
3.62
246.14
s71 −65
βHCC, ring 5
1457.66
12.6
15.74
s63 84
βHCC, (HCA)
1451.13
6.85
16.4
s54 −11
βHOC, (OCA)
1444.01
6.01
106.44
s29 −15 s69 10
υ
s (C–C), ring 5 + βHCC, ring 3
1422.52
3.56
1171.11
s22 34
υ
s (C=C), ring 2
1418.96
8.01
160.33
s62 11 s101 67
βHCH, (HCA) + τHCOC, (OCA)
1407.13
11.57
189.62
s31 −23 s64 −17
υ
as (C–C), ring 5 + βHCN, (NCA)
1387.02
4.94
692.54
s31 −11 s64 31
υ
as (C–C), ring 5 + βHCN, (NCA)
1371.3
53.01
744.64
s24 −51 s42 13
υ
as (C–C), ring 1 + υs (C–C), ring 5
1365.37
3.17
20.73
s85 10
βCCC, ring 4
1347.53
8.32
30.53
s37 −41 s66 −10
υ
as (C=C), ring 2 + βHCC, ring 4
1322.41
32.6
186.95
s56 −45
βHCC, ring 1
1301.85
0.32
18.48
s58 76
βHCC, (CAH)
1293.46
1.16
19.8
s33 12 s60 10 s68 21
υ
as (C–C), ring 3 + βHCC, ring 4 + βHCC, ring 5
1290.84
115.58
764.31
s30 58
υ
s (CO), (CAO)
1284.22
2.96
455.48
s41 20 s69 −17
υ
s (C–C), ring 5 + βHCC, ring 5
1264.63
151.27
24.03
s26 −16 s57 −14
υ
as (C–C), ring 5 + βHCC, ring 1
1263.15
62.22
3895.41
s41 −11 s44 −11
+υas (C–C), ring 1 + υas (C–C), ring 5
1252.17
107.36
376.98
Not defined
1231.74
194.37
485.07
s32 −10 s72 21
υ
as (C–C), ring 2 + βHCC, ring 5
1223.49
154.6
440.05
s70 −52
βHCC, ring 2
1211.31
266.52
575.9
s70 −13
βHCC, ring 2
1196.58
52.39
47.76
s25 17 s66 40
υ
s (C=C), ring 4 + βHCC, ring 5
1190.05
0.98
29.65
s39 14s65 49
υ
s (C=C), ring 3 + βHCC, ring 3
1188.46
5.77
4.66
s58 −14 s100 54
βHCC (CAH) + τHCOC, (OCA)
1163.11
62.3
4.06
s29 25s57 55
υ
s (C=C), ring 1 + βHCC, ring 1
1147.16
3.05
19.94
s48 22 s61 −18 s94 −12 s103 −32
βHCH (CAH) + βCCO (CAO) + τHCCO (OCA)
1143.32
0.51
14.59
s77 32
βCCC, ring 4
1132.55
18.83
225.65
s69 11
βHCC, ring 5
1118.58
268.59
4.61
s46 −31 s55 15
υ
as (C=C), ring 1 + βHCC, ring 1
1085.93
16.59
30.98
s27 14 s34 22
υ
s (C=C), ring 3 + υs (C=C), ring 5
1039.71
88.12
4.02
s47 72
υ
as (C=C), (CAH)
1037.69
2.7
6.89
s102 −80
τHCCC, ring 4
1015.71
1
19.59
s112 −52
τHCCC, ring 5
1014.43
16.39
160.22
s99 −66
τHCNC, (CAN)
1005.48
0.18
0.64
s113 61
τHCCC, ring 3
1004.51
5.05
79.88
s106 74
τHCCC, ring 1
995.67
6.4
4.17
s32 10 s40 −12
υ
s (C–C), ring 2 + υas (C=C), ring 3
982.59
1.21
30.45
s109 66
τHCCC, ring 2
966.87
5.99
189.31
s97 38
τHCCC, ring 1
964.36
22.39
3.01
s97 44
τHCCC, ring 1
957.27
80.57
1.93
s96 75
τHOCC (CAO)
938.59
1.65
4.09
s110 72
τHCCC, ring 5
925.25
33.74
166.09
s44 −11 s79 −27
υ
as (CAN) + βCCC, ring 4
881.43
111.2
18.99
s108 −60
τHCCC, ring 2
876.59
42.03
10.19
s48 −12 s107 25
υ
as (C–C), ring 1 + τHCCC, ring 4
867.61
38.53
2.37
s98 60
τHCCC, ring 1
866.7
25.46
2.94
s48 −16 s98 −21 s107 −12 s108 −14
Not defined
846.41
10.78
2.34
s50 −54
βCCC, ring 4
833.53
3.4
6.97
s107 14 s111 31
τHCCC, ring 1 + τHCCC, ring 3
830.77
0.38
2.5
s104 70
τHCCO, (CAO)
828.69
9.21
66.05
s111 21
τHCCC, ring 2
815.14
3.69
7.4
s128 −18
τCCCC, ring 5
804.43
1.77
4.67
s73 −27
βOCO, (CAO)
793.29
1.08
59.46
s43 20 s82 18
υ
s (C–C), ring 1 + βCCC, ring 4
778.97
8.82
4.11
s114 67
τHCCC, ring 5
764.69
5.88
9.65
s82 17
βCCC, ring 1
760.34
19.23
0.69
s136 −51
ϕCCCC, ring 1
741.78
17.23
0.25
s107 −12 s111 11 s116 −11
τHCCC, ring 1 + τHCCC, ring 4 + τCCCC, ring 5
724.92
6.87
6.4
s141 55
ϕOCOC, (CAO)
714.44
0.19
18.14
s28 −11 s49 16
υ
s (C–C), ring 3 + βCCC, ring 4
702.64
8.92
32.91
s120 −15 s138 −10 s140 −24
τCCCC, ring 1 + ϕCCCC, ring 2 + ϕCCCC, ring 3
676.97
30.47
11.99
s41 11 s93 14
υ
s (C–C), ring 1 + βCCO, (CAO)
651.45
14.72
11.48
s51 −35
βCCC, ring 1
640.97
13.61
40.41
s126 12 s129 −11
τCCNC, ring 1 + τCCCC, ring 1
622.1
2.3
28.46
s38 −13 s80 17
υ
s (C–C), ring 3 + βCCN, (CAN)
578.44
0.11
9.98
s41 10 s49 10
υ
s (C–C), ring 3 + βCCC, ring 5
568.57
2.75
12.66
s121 −11 s122 −12 s124 −11s139 15
Not defined
559.84
0.71
13.11
s122 23 s124 10 s134 19
τCCCC, ring 1 + τCCCC, ring 3 + ϕCCCC, ring 5
546.17
11.74
2.14
Not defined
537.81
3.67
6.23
s52 24
βCCO, (CAO)
530.02
1.06
12.8
s117 24 s139 13
τCCCN, (CAN) + ϕCCCC, ring 3
521.45
3.05
74.21
s125 22 s127 14
τCCCC, ring 3 + τCCNC, (CAN)
512.46
0.83
1.44
s88 23
βCCC, ring 3
497.39
3.19
11.62
s76 −14 s83 11 s85 −15
βCCC, ring 3 + βCCN (CAN) + βCCC, ring 5
483.98
2.27
2.37
s123 −24 s135 24
τCCCC, ring 1 + ϕCCCC, ring 2
460.5
1.9
6.03
s87 20
βCCC, ring 4
444.53
1.19
3.6
s124 10
τCCCC, ring 1
432.84
0.68
21.66
s91 41
βCCO (CAO)
415.6
2.46
89.07
s22 −11 s90 −14
υ
as (C–C), ring 4 + βCCC, ring 3
386.89
0.5
1.35
s86 −10
βCCC, ring 2
372.32
11.47
1.34
s75 −16s94 56
βCOC, (CAO) + βCCO, (CAO)
355.13
1.38
4.26
s123 19 s135 10
τCCCC, ring 3 + ϕCCCC, ring 5
346.91
3.4
73.7
s115 −11
τNCCC, (CAN)
311.17
4.64
20.43
s45 −15 s95 31
υ
as (C–C), ring 4 + βCOC, (CAO)
289.37
5.1
68.61
s115 24
τNCCC, (CAN)
273
0.46
2.42
s105 −10 s121 17 s139 15
τCCCO, (CAO) + τCCCC, ring 3 + ϕCCCC, ring 5
267.89
0.58
7.14
s75 13
βCOC, (CAO)
252.25
1.23
10.57
s103 12s105 55
τCCCO, (CAO)
241.04
2.81
9.87
s75 12
βCOC, (CAO)
223.33
8.26
10.27
s138 −43
ϕCCCC, ring 4
186.81
5.98
7.28
s89 12s116 −17
βCCC, (CA) + τCCCN, (CAN)
171.6
0.34
10.17
Not defined
152.06
7.4
9.77
s118 24 s133 37
τCCCC, ring 1 + ϕCOCC, (CAO)
134.24
3.04
26.07
s75 −10
βCOC (CAO)
122.64
0.08
11.46
s119 15 s129 −11
τCCCN, (CAN) + τCCNC, (CAN)
100.65
1.28
6.44
s119 10 s127 14
τCCCN, (CAN) + τCCNC, (CAN)
92.61
0.67
7.41
s118 11 s131 −15 s133 −20 s134 13
τCOCC, (CAO)
79.9
0.64
3.96
s92 23 s131 12
βCCC, ring 4 + τCOCC, (CAO)
59.62
0.88
2.9
s130 −16 s131 −37
τCOCC, (CAO)
39.59
0.12
2.58
s130 48 s131 13 s132 −11
τCOCC, (CAO)
31.93
0.14
5.25
s74 −42
βCNC (CAN)
21.6
0.27
6.59
s126 12 s132 47
τCCNC, (CAN) + τCOCC, (CAO)
16.34
0.3
8.44
s126 18 s132 −22 s135 12
τCCNC, (CAN) + τCOCC, (CAO) + ϕCCCC, ring 3
υ, β, τ, and ϕ denote the stretching, bending, torsion, and out (ϕ ABCD means the angle between the AD vector and the BCD plane) modes. Indices notation: s: symmetric; as: asymmetric; A: aliphatic; ring 1: C1-C2-C3-C4-C5-C6; ring 2: C15-C16-C17-C18-C19-C20; ring 3: C21-C22-C23-C24-C16-C17; ring 4: C17-C18-C24-C25-C26-C27; ring 5: C23-C24-C25-C28-C29-C30.


### 4.6.1. Ring, C=O and C=N Vibrations

The C–H stretching vibrations in the range 2800–3200 cm−1 are for aromatic compounds. From the PED analysis we found that C–H stretching vibrations for ring 1 are assigned at 3183 cm−1. This mode is very pure mode as its PED analysis is about 99%. The values observed in the range (3158–3224) cm−1 are assigned to the stretching vibrations of methyl hydrogen’s while their experimentally obtained counterparts are at 3200 cm−1 and 3118 cm−1, respectively. The percentage of PED calculated for these modes by VEDA 4 program varies from 92 to 99% indicating that they are pure modes. C–N modes of vibrations are assigned on the basis of PED calculations. In the PED analysis we found that C–N modes of vibrations are at 1407 and 1387 cm−1 respectively, however these modes are not pure modes and are mixed with C–C stretching modes, while experimentally observed value is at 1611 cm−1. On the basis of PED analysis the wavenumbers at 1648, 1643, 1675, 1554, and 1526 cm−1 are assigned to C=O stretching modes, however again these modes are not pure modes and are mixed with other modes of vibrations. Experimentally obtained values for C=O stretching modes is at 1649 cm−1. The PED analysis for various modes of the title compound along with their percentage values are summarized in Table 5.


## 4.6.1. Ring, C=O and C=N Vibrations

The C–H stretching vibrations in the range 2800–3200 cm−1 are for aromatic compounds. From the PED analysis we found that C–H stretching vibrations for ring 1 are assigned at 3183 cm−1. This mode is very pure mode as its PED analysis is about 99%. The values observed in the range (3158–3224) cm−1 are assigned to the stretching vibrations of methyl hydrogen’s while their experimentally obtained counterparts are at 3200 cm−1 and 3118 cm−1, respectively. The percentage of PED calculated for these modes by VEDA 4 program varies from 92 to 99% indicating that they are pure modes. C–N modes of vibrations are assigned on the basis of PED calculations. In the PED analysis we found that C–N modes of vibrations are at 1407 and 1387 cm−1 respectively, however these modes are not pure modes and are mixed with C–C stretching modes, while experimentally observed value is at 1611 cm−1. On the basis of PED analysis the wavenumbers at 1648, 1643, 1675, 1554, and 1526 cm−1 are assigned to C=O stretching modes, however again these modes are not pure modes and are mixed with other modes of vibrations. Experimentally obtained values for C=O stretching modes is at 1649 cm−1. The PED analysis for various modes of the title compound along with their percentage values are summarized in Table 5.


## 4.7. NBO Analysis

In order to understand the hyper conjugation as well as delocalization of the title compound we have investigated the natural bond orbital analysis of the title compound using NBO 3.1 program implemented in Gaussian 09 package [25]. We have used DFT/B3LYP/6-311++G(2d, 2p) level of theory in order to understand different kind of interactions between the filled and the vacant orbitals. We can investigate both intra- and intermolecular interactions using NBO analysis. In addition to this NBO analysis is also useful for understanding charge transfer conjugative interactions in different compounds. Using DFT/B3LYP/6-311++G(2d, 2p) level of theory the second-order perturbation theory analysis of Fock matrix in NBO basis [26] for title compound is listed in Table 6. For each donor (i) and acceptor (j) the stabilization energy E(2) associated with the delocalization i→j is determined as
(1)E(2)=ΔEijqi(Fij)2(Ej-Ei).
Large E(2) value shows the intensive interaction between electron-donors and electron-acceptors groups and greater extent of conjugation of the whole system. The possible intensive interactions are also listed in Table 6. The second-order perturbation theory analysis of Fock matrix in NBO basis shows strong intramolecular hyper conjugative interactions of π electrons. From Table 6 we can see that the intramolecular hyper conjugative interactions are formed by the orbital overlap between oxygen, nitrogen, and carbon-carbon bond orbitals. This orbital overlapping is responsible for ICT causing stabilization of the system under study. From the analysis of Table 6 we found that the strong intramolecular hyper conjugative interaction is of C7–O9 from n2(O8)→π* (C7–O9)which increases ED (0.10070 e) that weakens the respective bonds leading to stabilization of 32.78 kcal mol−1. Similarly another strong intramolecular hyper conjugative interaction of C7–O8 from n2(O9)→π*(C7–O8) increases ED (0.28565 e) that weakens the respective bonds leading to stabilization of 46.67 kcal mol−1. We have also found another strong intramolecular hyper conjugative interaction of C21–C22 from n1(C23)→π* (C21–C22) which increases ED (0.18831 e) that also weakens the respective bonds leading to stabilization of 46.88 kcal mol−1. We predicted one more strong intramolecular hyper conjugative interaction of C21–C22 from n1(C23)→π*(C21–C22) which increases ED (0.18831 e) that weakens the respective bonds leading to stabilization of 46.88 kcal mol−1, as well as strong intramolecular hyper conjugative interaction of C24–C25 from n1(C23)→π*(C24–C25) which increases ED (0.46625 e) that weakens the respective bonds leading to stabilization of 71.49 kcal mol−1. These interactions are observed as an increase in electron density (ED) in C–C antibonding orbitals that weakens the respective bonds.Table 6
Second-order perturbation theory analysis of Fock matrix in NBO basis.
Donor (i)
Type
ED/e
Acceptor (j)
Type
ED/e
E(2)a (kcalmol−1)
E
(
j
)
-
E
(
i
)
b (a.u)
F
(
i
,
j
)
c
(a.u)
C1–C2
π
1.68952
C3–C4
π
*
0.45595
25.08
0.26
0.075
C1–C2
π
1.68952
C5–C6
π
*
0.35531
15.88
0.28
0.060
C1–C6
σ
1.63511
C9–C10
σ
*
0.34194
4.65
1.25
0.068
C3–C4
π
1.55498
C1–C2
π
*
0.27464
13.45
0.29
0.058
C3–C4
π
1.55498
C5–C6
π
*
0.35531
25.35
0.28
0.077
C3–C4
π
1.55498
C13–N14
π
*
0.21940
23.30
0.25
0.072
C5–C6
π
1.65905
C1–C2
π
*
0.27464
22.39
0.28
0.072
C5–C6
π
1.65905
C1–C2
π
*
0.45595
15.42
0.26
0.059
C5–C6
π
1.65905
C7–O8
π
*
0.28565
27.55
0.24
0.074
C13–C14
π
1.91336
C3–C4
π
*
0.45595
6.89
0.94
0.023
C13–C14
π
1.91336
C15–C16
π
*
0.44368
9.43
0.37
0.058
C15–C16
π
1.96604
C13–N14
π
*
0.21940
11.21
0.24
0.049
C15–C16
π
1.96604
C17–C18
π
*
0.46912
19.03
0.28
0.066
C15–C16
π
1.96604
C19–C20
π
*
0.32861
19.83
0.27
0.067
C15–C16
π
1.96604
C21–C22
π
*
0.18831
15.74
0.29
0.064
C17–C18
π
1.52506
C15–C16
π
*
0.44368
20.29
0.26
0.066
C17–C18
π
1.52506
C19–C20
π
*
0.32861
19.87
0.26
0.066
C17–C18
π
1.52506
C24–C25
π
*
0.46625
19.54
0.27
0.065
C17–C18
π
1.52506
C26–C27
π
*
0.19336
14.49
0.28
0.061
C19–C20
π
1.68814
C15–C16
π
*
0.44368
19.18
0.28
0.068
C19–C20
π
1.68814
C17–C18
π
*
0.46912
17.64
0.29
0.066
C21–C22
π
1.79067
C15–C16
π
*
0.44368
17.23
0.28
0.066
C24–C25
π
1.53004
C17–C18
π
*
0.46912
20.01
0.27
0.065
C24–C25
π
1.53004
C26–C27
π
*
0.19336
14.62
0.27
0.061
C26–C27
π
1.79745
C17–C18
π
*
0.46912
14.32
0.29
0.062
C26–C27
π
1.79745
C24–C25
π
*
0.46625
14.02
0.30
0.062
LP(2)O8
n
1.86096
C6–C7
σ
*
0.05894
15.13
0.69
0.093
LP(2)O8
n
1.86096
C7–O9
σ
*
0.10070
32.78
0.57
0.123
LP(1)O9
n
1.96939
C7–O8
σ
*
0.01769
6.52
1.08
0.075
LP(2)O9
n
1.80240
C7–O8
π
*
0.28565
46.67
0.30
0.108
LP(2)O9
n
1.80240
C7–O8
π
*
0.28565
46.67
0.30
0.108
LP(1)O12
n
1.97419
C3–C4
σ
0.04045
7.37
1.05
0.079
LP(2)O12
n
1.79696
C3–C4
π
*
0.45595
37.12
0.31
0.102
LP(1)N14
n
1.84279
C3–C4
σ
*
0.03276
10.67
0.74
0.082
LP(1)C23
n
0.99827
C21–C22
π
*
0.18831
48.68
0.14
0.097
LP(1)C23
n
0.99827
C24–C25
π
*
0.46625
71.49
0.14
0.103
LP(1)C23
n
0.99827
C21–C22
π
*
0.33071
68.23
0.13
0.104
a
E(2) means stabilization energy.
bEnergy difference between the donor and acceptor NBO orbitals.
c
F
(
i
,
j
) is the Fock matrix element between i and j NBO orbitals.


## 5. Conclusions

Using DFT/B3LYP/6-311++G(2d, 2p) level of theory a detailed study of molecular structure, NMR chemical shifts, electronic properties, MEP surface mapping, NBO analysis, and vibrational and PED analysis of the title compound has been investigated and reported. On comparison with experimentally obtained parameters by one of coauthors of this paper we found that both of them are in agreement with each other. HOMO-LUMO analysis of the title compound shows that the electron charge distribution is mainly concentrated over the rings and there may be a charge transfer throughπ system which accounts for bioactivity of the molecule. The title compound has also large band gap as reported in HOMO-LUMO analysis which accounts for its future applications as a useful material in solar cell devices. Molecular electrostatic surface maps give an idea about the chemical reactivity of the title compound. Our overall simulated results for different molecular properties of the title compound are obtained for the first time and we hope that they are helpful in the synthesis and design of new applications.



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*Source: 841593-2014-07-09.xml*