Abstract
In this study, the structure of 4-[4-(diethylamino)-benzylideneamino]-5-benzyl-2H-1,2,4-triazol-3(4H)-one (DBT) was examined through spectroscopic and theoretical analyses. In this respect, the geometrical, vibrational frequency, 1H and 13C-nuclear magnetic resonance (NMR) chemical shifts, thermodynamic, hyperpolarizability, and electronic properties including the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energies of DBT as a potential non-linear optical (NLO) material were investigated using density functional theory at the B3LYP level with the 6-311G basis set. 1H and 13C-NMR chemical shifts of DBT with the gauge-invariant atomic orbital and continuous set of gauge transformation methods (in the solvents) were estimated, and the computed chemical shift values displayed excellent alignment with observed ones. Time-dependent density-functional theory (TD-DFT) calculations with the integral equation formalism polarizable continuum model within various solvents and gas phases in the ground state were used to evaluate UV-vis absorption and fluorescence emission wavelengths. Thermodynamic parameters including enthalpy, heat capacity, and entropy for DBT were also calculated at various temperatures. Moreover, calculations of the NLO were carried out to obtain the title compound’s electric dipole moment and polarizability properties. To illustrate the effect of the theoretical method on the spectroscopic and structural properties of DBT, experimental data of structural and spectroscopic parameters were used. The correlational analysis results were observed to indicate a strong relationship between the experimental and theoretical results.
Graphical abstract
1 Introduction
1,2,4-Triazole and its heterocyclic derivatives have drawn much attention in recent years on account of their structural properties such as ease of accessibility and good coordination diversity, the existence of π-conjugated heterocyclic system possessing good coordination abilities, the existence of nitrogen atoms as receptors of hydrogen bonds along with aromatic systems that contribute to π–π stacking leading to a variety of secondary non-covalent interactions [1,2,3,4,5,6,7,8]. However, their wide range of biological uses, such as the broad spectrum of biological activity, materials with optoelectronic properties, electrochemical applications, and possible energetic materials, have generated substantial interest in these compounds [9,10,11,12].
Schiff bases have a wide range of applications in many fields, including analytical chemistry, material science, and biological and pharmaceutical research. In this respect, the heterocyclic derivatives of Schiff bases derived from 1,2,4-triazole display a wide variety of biological activities such as anti-inflammatory, antibacterial, antifungal, and antileishmanial antitubercular, antioxidant, analgesic, antitumor, and pesticidal properties [13,14,15,16,17,18]. In the past two decades, a considerable amount of literature has been published on their synthesis, pharmacological, and biological properties [19,20,21,22,23,24].
Over the last decade, extensive experimental and theoretical research on the structural, spectral, electronic, and thermal properties of non-linear optical (NLO) materials has been conducted due to their prospective uses in laser technology, optical communication, visual information processing, and high-density optical disc data storage. The research for new and improved NLO materials is vital to meet the demands of evolving technologies. Particularly, molecular systems having π-conjugate demonstrate a significant NLO response, and these systems are thus extensively explored [25,26,27,28,29].
A comprehensive literature survey shows that neither theoretical calculation nor extensive spectroscopic analysis has yet been published on the structure of 4-[4-(diethylamino)-benzylideneamino]-5-benzyl-2H-1,2,4-triazol-3(4H)-one (DBT). Therefore, the primary purpose of this investigation is to develop an understanding of the structural, electrical, and spectroscopic, thermodynamic, and NLO properties for DBT through experimental and theoretical methods. This study will focus on the structural, electrical, thermal, NLO, and spectroscopic properties of 1,2,4-triazole-based azomethine, DBT, in the light of DFT-based quantum chemical calculations.
2 Materials and methods
2.1 Computational details
In accordance with the aims of the study, the optimized molecular structures, 1H and 13C nuclear magnetic resonance (NMR) chemical changes, vibrational frequencies, UV-vis spectroscopy properties, thermodynamic properties, atomic charges, and frontier molecule orbitals of DBT were determined using the DFT/B3LYP method with the 6-311G basis set. All calculations were conducted with the Gauss-View and Gaussian09 molecular programs [30,31]. The accurate molecular structure and vibrational calculations of DBT were computed using Becke-3-Lee Yang-Parr [32,33] density functional methods with the 6-311G basis set. The measured vibrational wavenumbers for the optimized molecular structure showed that the structure was stable. However, the values computed for vibrational wavenumbers involved the known systematic errors [17]. Therefore, the determined vibrational wavenumbers were scaled to 0.9614, ranging from 1,700 to 4,000 cm−1, and scaled to 1.0013 below 1,700 cm−1 for the B3LYP/6-311G basis set. In addition, fundamental molecular vibration mode assignments were conducted using the VEDA 4 program based on the analysis of total energy distribution [34]. The optimized molecular geometries for NMR calculations of DBT were first obtained with 6-311G basis set in the gas phase (ε = 1), CCl4 (ε = 2.24), CHCl3 (ε = 4.9), and DMSO (ε = 46.7) solvents through the system of integral equation formalism polarizable continuum model. The 1H and 13C NMR chemical shifts of DBT in different solvents were determined with the gauge-invariant atomic orbital (GIAO) and continuous set of gauge transformation (CSGT) methods at the B3LYP/6-311G basis set [35,36,37,38,39,40,41]. In the same way, UV-vis spectroscopic computations of DBT were conducted utilizing the TD-DFT/B3LYP method in the CHCl3 (ε = 4.9), ethanol (ε = 24,5), and water (ε = 78.39) solvents [42]. In addition, HOMO-1, HOMO, LUMO, and LUMO+1 energies and energy gaps of DBT were determined through the B3LYP/6-311G basis set. Meanwhile, the orbital shapes (HOMO-1, HOMO, LUMO, and LUMO+1) of the mentioned molecule were mapped in three-dimensional (3D) with the B3LYP/6-311G basis set. Using the optimized molecular structure with the B3LYP/6-311G basis set, the molecular electrostatic potential (MEP) map of DBT was drawn. Finally, Mulliken atomic charges, thermodynamic characteristics (i.e., enthalpy, entropy, and thermal capacity) at various temperatures, and NLO properties (i.e., the first hyperpolarizability and polarizability) of DBT were examined.
3 Results and discussion
3.1 Molecular structure
The optimized molecular structure for DBT is presented in Figure 1. The optimized molecular geometric properties (bond lengths, bond angles, and dihedral angles) of DBT are given in Table 1.
The chemical structure (top) and optimized molecular 50 structure (bottom) for DBT.
The calculated bond lengths, dihedral angles and bond angles for DBT
| Bond lengths (Å) | B3LYP | Bond angles (°) | B3LYP | Dihedral angles (°) | B3LYP |
|---|---|---|---|---|---|
| C1–C14 | 1.495 | C14–C1–N45 | 126.404 | N45–C1–C14–C15 | 0.799 |
| C1–N45 | 1.314 | C14–C1–N46 | 122.391 | N45–C1–C14–H37 | 124.048 |
| C1–N46 | 1.396 | N45–C1–N46 | 111.205 | N45–C1–C14–H38 | −122.445 |
| C2–N44 | 1.374 | N44–C2–N46 | 101.767 | N46–C1–C14–C15 | −179.274 |
| C2–N46 | 1.421 | N44–C2–O49 | 129.621 | N46–C1–C14–H37 | −56.026 |
| C2–O49 | 1.249 | N46–C2–O49 | 128.613 | N46–C1–C14–H38 | 57.482 |
| C3–C4 | 1.453 | C4–C3–H22 | 117.736 | C14–C1–N45–N44 | 179.939 |
| C3–H22 | 1.084 | C4–C3–N47 | 120.766 | N46–C1–N45–N44 | 0.005 |
| C3–N47 | 1.303 | H22–C3–N47 | 121.498 | C14–C1–N46–C2 | −179.958 |
| C4–C5 | 1.409 | C3–C4–C5 | 123.224 | C14–C1–N46–N47 | 0.136 |
| C4–C9 | 1.407 | C3–C4–C9 | 119.426 | N45–C1–N46–C2 | −0.021 |
| C5–C6 | 1.384 | C5–C4–C9 | 117.349 | N45–C1–N46–N47 | −179.928 |
| C5–H23 | 1.081 | C4–C5–C6 | 121.493 | N46–C2–N44–H21 | −179.958 |
| C6–C7 | 1.423 | C4–C5–H23 | 118.776 | N46–C2–N44–N45 | −0.026 |
| C6–H24 | 1.078 | C6–C5–H23 | 119.731 | O49–C2–N44–H21 | 0.045 |
| C7–C8 | 1.419 | C5–C6–C7 | 121.406 | O49–C2–N44–N45 | 179.978 |
| C7–N48 | 1.391 | C5–C6–H24 | 118.321 | N44–C2–N46–C1 | 0.027 |
| C8–C9 | 1.388 | C7–C6–H24 | 120.273 | N44–C2–N46–N47 | 179.922 |
| C8–H25 | 1.078 | C6–C7–C8 | 116.852 | O49–C2–N46–C1 | −179.976 |
| C9–H26 | 1.083 | C6–C7–N48 | 121.494 | O49–C2–N46–N47 | −0.081 |
| C10–C11 | 1.537 | C8–C7–N48 | 121.652 | H22–C3–C4–C5 | 179.360 |
| C10–H27 | 1.091 | C7–C8–C9 | 121.066 | H22–C3–C4–C9 | −0.558 |
| C10–H28 | 1.092 | C7–C8–H25 | 120.547 | N47–C3–C4–C5 | −0.889 |
| C10–N48 | 1.473 | C9–C8–H25 | 118.387 | N47–C3–C4–C9 | 179.193 |
| C11–H29 | 1.093 | C4–C9–C8 | 121.823 | C4–C3–N47–N46 | −179.815 |
| C11–H30 | 1.091 | C4–C9–H26 | 119.263 | H22–C3–N47–N46 | −0.074 |
| C11–H31 | 1.090 | C8–C9–H26 | 118.914 | C3–C4–C5–C6 | 179.886 |
| C12–C13 | 1.538 | C11–C10–H27 | 109.435 | C3–C4–C5–H23 | −0.348 |
| C12–H32 | 1.091 | C11–C10–H28 | 110.085 | C9–C4–C5–C6 | −0.195 |
| C12–H33 | 1.092 | C11–C10–N48 | 114.735 | C9–C4–C5–H23 | 179.571 |
| C12–N48 | 1.473 | H27–C10–H28 | 106.001 | C3–C4–C9–C8 | −179.854 |
| C13–H34 | 1.090 | H27–C10–N48 | 107.093 | C3–C4–C9–H26 | 0.288 |
| C13–H35 | 1.090 | H28–C10–N48 | 109.096 | C5–C4–C9–C8 | 0.224 |
| C13–H36 | 1.093 | C10–C11–H29 | 110.212 | C5–C4–C9–H26 | −179.635 |
| C14–C15 | 1.516 | C10–C11–H30 | 111.051 | C4–C5–C6–C7 | −0.513 |
| C14–H37 | 1.093 | C10–C11–H31 | 111.431 | C4–C5–C6–H24 | 179.326 |
| C14–H38 | 1.093 | H29–C11–H30 | 108.026 | H23–C5–C6–C7 | 179.724 |
| C15–C16 | 1.401 | H29–C11–H31 | 108.126 | H23–C5–C6–H24 | −0.438 |
| C15–C20 | 1.401 | H30–C11–H31 | 107.870 | C5–C6–C7–C8 | 1.148 |
| C16–C17 | 1.397 | C13–C12–H32 | 109.432 | C5–C6–C7–N48 | −178.253 |
| C16–H39 | 1.083 | C13–C12–H33 | 110.081 | H24–C6–C7–C8 | −178.687 |
| C17–C18 | 1.397 | C13–C12–N48 | 114.717 | H24–C6–C7–N48 | 1.912 |
| C17–H40 | 1.082 | H32–C12–H33 | 106.029 | C6–C7–C8–C9 | −1.116 |
| C18–C19 | 1.397 | H32–C12–N48 | 107.094 | C6–C7–C8–H25 | 178.838 |
| C18–H41 | 1.082 | H33–C12–N48 | 109.094 | N48–C7–C8–C9 | 178.284 |
| C19–C20 | 1.396 | C12–C13–H34 | 111.450 | N48–C7–C8–H25 | −1.763 |
| C19–H42 | 1.082 | C12–C13–H35 | 111.004 | C6–C7–N48–C10 | −0.283 |
| C20–H43 | 1.083 | C12–C13–H36 | 110.195 | C6–C7–N48–C12 | −179.649 |
| H21–N44 | 1.001 | H34–C13–H35 | 107.882 | C8–C7–N48–C10 | −179.655 |
| N44–N45 | 1.409 | H34–C13–H36 | 108.125 | C8–C7–N48–C12 | 0.979 |
| N46–N47 | 1.394 | H35–C13–H36 | 108.064 | C7–C8–C9–C4 | 0.455 |
| C1–C14–C15 | 114.125 | C7–C8–C9–H26 | −179.686 | ||
| C1–C14–H37 | 108.134 | H25–C8–C9–C4 | −179.499 | ||
| C1–C14–H38 | 108.156 | H25–C8–C9–H26 | 0.360 | ||
| C15–C14–H37 | 110.384 | H27–C10–C11–H29 | −61.307 | ||
| C15–C14–H38 | 110.368 | H27–C10–C11–H30 | 58.365 | ||
| H37–C14–H38 | 105.260 | H27–C10–C11–H31 | 178.649 | ||
| C14–C15–C16 | 120.623 | H28–C10–C11–H29 | 54.812 | ||
| C14–C15–C20 | 120.644 | H28–C10–C11–H30 | 174.484 | ||
| C16–C15–C20 | 118.732 | H28–C10–C11–H31 | −65.231 | ||
| C15–C16–C17 | 120.724 | N48–C10–C11–H29 | 178.315 | ||
| C15–C16–H39 | 119.481 | N48–C10–C11–H30 | −62.013 | ||
| C17–C16–H39 | 119.794 | N48–C10–C11–H31 | 58.271 | ||
| C16–C17–C18 | 120.090 | C11–C10–N48–C7 | −82.396 | ||
| C16–C17–H40 | 119.823 | C11–C10–N48–C12 | 96.990 | ||
| C18–C17–H40 | 120.087 | H27–C10–N48–C7 | 155.940 | ||
| C17–C18–C19 | 119.637 | H27–C10–N48–C12 | −24.674 | ||
| C17–C18–H41 | 120.181 | H28–C10–N48–C7 | 41.632 | ||
| C19–C18–H41 | 120.182 | H28–C10–N48–C12 | −138.982 | ||
| C18–C19–C20 | 120.094 | H32–C12–C13–H34 | −178.801 | ||
| C18–C19–H42 | 120.080 | H32–C12–C13–H35 | −58.521 | ||
| C20–C19–H42 | 119.826 | H32–C12–C13–H36 | 61.157 | ||
| C15–C20–C19 | 120.723 | H33–C12–C13–H34 | 65.049 | ||
| C15–C20–H43 | 119.477 | H33–C12–C13–H35 | −174.671 | ||
| C19–C20–H43 | 119.801 | H33–C12–C13–H36 | −54.994 | ||
| C2–N44–H21 | 126.194 | N48–C12–C13–H34 | −58.435 | ||
| C2–N44–N45 | 113.897 | N48–C12–C13–H35 | 61.845 | ||
| H21–N44–N45 | 119.908 | N48–C12–C13–H36 | −178.477 | ||
| C1–N45–N44 | 104.322 | C13–C12–N48–C7 | 81.387 | ||
| C1–N46–C2 | 108.808 | C13–C12–N48–C10 | −98.000 | ||
| C1–N46–N47 | 120.918 | H32–C12–N48–C7 | −156.963 | ||
| C2–N46–N47 | 130.273 | H32–C12–N48–C10 | 23.650 | ||
| C3–N47–N46 | 118.998 | H33–C12–N48–C7 | −42.622 | ||
| C7–N48–C10 | 121.243 | H33–C12–N48–C10 | 137.991 | ||
| C7–N48–C12 | 121.058 | C1–C14–C15–C16 | 91.215 | ||
| C10–N48–C12 | 117.696 | C1–C14–C15–C20 | −89.136 | ||
| H37–C14–C15–C16 | −30.806 | ||||
| H37–C14–C15–C20 | 148.843 | ||||
| H38–C14–C15–C16 | −146.748 | ||||
| H38–C14–C15–C20 | 32.900 | ||||
| C14–C15–C16–C17 | 179.609 | ||||
| C14–C15–C16–H39 | −0.525 | ||||
| C20–C15–C16–C17 | −0.046 | ||||
| C20–C15–C16–H39 | 179.820 | ||||
| C14–C15–C20–C19 | −179.611 | ||||
| C14–C15–C20–H43 | 0.562 | ||||
| C16–C15–C20–C19 | 0.044 | ||||
| C16–C15–C20–H43 | −179.784 | ||||
| C15–C16–C17–C18 | 0.018 | ||||
| C15–C16–C17–H40 | −179.948 | ||||
| H39–C16–C17–C18 | −179.848 | ||||
| H39–C16–C17–H40 | 0.187 | ||||
| C16–C17–C18–C19 | 0.012 | ||||
| C16–C17–C18–H41 | −179.939 | ||||
| H40–C17–C18–C19 | 179.978 | ||||
| H40–C17–C18–H41 | 0.026 | ||||
| C17–C18–C19–C20 | −0.014 | ||||
| C17–C18–C19–H42 | −179.986 | ||||
| H41–C18–C19–C20 | 179.938 | ||||
| H41–C18–C19–H42 | −0.034 | ||||
| C18–C19–C20–C15 | −0.014 | ||||
| C18–C19–C20–H43 | 179.813 | ||||
| H42–C19–C20–C15 | 179.957 | ||||
| H42–C19–C20–H43 | −0.216 | ||||
| C2–N44–N45–C1 | 0.014 | ||||
| H21–N44–N45–C1 | 179.951 | ||||
| C1–N46–N47–C3 | 179.938 | ||||
| C2–N46–N47–C3 | 0.055 |
Figure 1 shows the optimized molecular structure of DBT together with the atom numbering system. A potential energy surface analysis was performed to demonstrate the orientation of the imine group and phenyl in DBT. Scanning of the whole potential energy surface around N47–C3–C4–C9 was carried out using the DFT/B3LYP/6-311G level of theory. All the geometrical parameters were simultaneously relaxed during the computation, while the N47–C3–C4–C9 torsional angles were varied in steps of 0, 1, 2, 3,…, 360°. According to the potential energy surface diagram, it was observed that the C1 configuration had the lowest energy structure. The energies of C1, C2, and C3 conformations were observed to be −1124.87163 a.u. (for C1), −1124.85626 a.u. (for C2), and −1124.85629 a.u. (for C3), respectively (Figure 2). The structure was then re-optimized using the DFT/B3LYP method, using the 6-311G basis set. The optimized geometry of DBT confirmed that the vibrational spectrum did not contain imaginary wavenumbers on true local minimum on the potential energy surface.
The scanned potential energy surface for DBT with DFT/B3LYP/6-311G level.
In contrast, the calculated values were observed to agree with the X-ray results [43]. The phenyl ring’s C–C bond lengths were changed due to the introduction of the triazole ring, imine, and diethylamino group in DBT. The shortest C1–C14 bond length was 1.495 Å, while the longest C5–C6 bond was noted to be 1.384 Å by DFT/6-311G. The C–C bond lengths in the aromatic ring were recorded to be in the range of about 1.380–1.405 Å by Kalaichelvan et al. [44]. The computed C–N (C1–N46, C2–N46, C2–N44, triazole, and C7–N48, C10–N48, and C12–N48 in triazole ring) bond lengths were at 1.396, 1.421, and 1.374 Å in triazole ring and 1.391, 1.473, and 1.473 Å in the ring, respectively. In contrast, the experimentally observed C–N (C1–N46, C2–N46, and C2–N44) bond lengths in the triazole ring were 1.348, 1.329, and 1.377 Å, respectively [43]. The computed bond lengths of double-bonded C1═N44 in triazole ring and C3═N47 in the imine group for DBT were 1.314 and 1.303 Å, while the bond lengths of some similar structure were reported to be at the interval of 1.300–1.320 Å [45]. Furthermore, the calculated N–N (N44–N45 and N45–N47) bond lengths in the 4-amino-1,2,4-triazole ring were 1.409 and 1.394 Å, respectively. These bond lengths were recorded as 1.380 Å for related structures [43]. The double-bonded C2═O10 bond length was determined to be 1.249 Å, which reasonably agreed with previously published values for related structures [46]. The N–H length was computed as the shortest bond in this structure with 1.001 Å. The N–H length value for related structures had been found at 0.990 Å in the literature [43]. The lengths of all C–H bonds in aromatic rings were measured in the range of 1.050–1.010 Å and agreed well with the lengths of C–H bonds in aromatic rings [44]. The N46–C1–N45 bond angle of DBT was observed to be 101.767°, and the value reported for similar structures in literature was 113.8° [43]. Moreover, the computed triazole C1–N46–C2 and N46–C2–N44 bond angles were at 108.808 and 101.767°, while bond angles reported for triazole ring were found to be 105.7 and 108.7° in the literature [43]. The geometric parameters computed by utilizing the B3LYP method and the 6-311G level were in good agreement with the experimental results in the literature [43,44,45,46].
3.2 Vibrational frequencies
The DBT had 45 atoms, and thus the standard vibration numbers were 129. All vibrations under C 1 symmetry were active in IR. The observed and computed vibrational frequencies, IR intensities, and assignments for DBT are summarized in Table 2. Moreover, the experimental IR and simulated spectra of DBT by utilizing the B3LYP/6-311G level are presented in Figure 3. In order to make a comparison between the computed wavenumbers and experimental ones, the linear correlation coefficients (R 2) shown in Table 2 are displayed in Figure 4, as well. Here, we have reported the (R 2) value of DBT as (R 2) = 0.9867 for the IR wavenumbers.
Experimental and calculated (unscaled and scaled) B3LYP/6-311G level vibrational frequencies (cm−1), IR intensity (km mol−1), Raman intensity, force constant (mdyne Å−1) and probable assignments for DBT
| Experimental frequencies | B3LYP 6-311G | Characterization of normal modes with potential energy distribution (PED) (%) | ||||
|---|---|---|---|---|---|---|
| FTIRa | Unscaled | Scaled | IR intensity I IR | Raman intensity S Raman | ||
| 1 | — | 10 | 10 | 0.01 | 2.79 | τCCCC (17) in ring + τCNNC (58) in triazole |
| 2 | — | 15 | 15 | 0.13 | 6.07 | [τCNNC (20) + γNCCN (12)] in triazole + [τCCCC(13) + τCNCC (12) + τCNCC (12)] in ring |
| 3 | — | 29 | 28 | 0.32 | 3.56 | δC3N47N46 (20) + δN3C1C14 (13) + δC4C3N47 (23) |
| 4 | — | 30 | 29 | 0.12 | 5.74 | τCNNC(33) in triazole + τCCCC (40) in ring |
| 5 | — | 36 | 35 | 0.31 | 0.2 | τCCCC (56) in ring |
| 6 | — | 45 | 43 | 0.63 | 1.55 | τCNNC (10) in triazole + τCCCC (14) + τCNCC (22) + τCCNC (22) in ring |
| 7 | — | 73 | 70 | 0.36 | 2.55 | δCCC (15) + γCCCC (26) in ring |
| 8 | — | 85 | 81 | 0.21 | 0.46 | τCNNC (10) + τNCCNN (16) + τCCCN (12) + τNCCN (22) in triazole |
| 9 | — | 102 | 98 | 0.68 | 2.42 | τCCNC(68) in ring |
| 10 | — | 104 | 100 | 0.13 | 1.53 | τCNCC (23) + τCCNC (32) in ring |
| 11 | — | 123 | 119 | 2.61 | 2.1 | τNNCC(25) + γNCNC (10) in triazole + γCCCN (17) in ring |
| 12 | — | 146 | 140 | 2.98 | 1.87 | [δNCCimine (17) + τCCNC (12)] in triazole ring |
| 13 | — | 161 | 155 | 1.29 | 1.52 | [τNNCC (31) + γNCNC (10)] in triazole ring |
| 14 | — | 178 | 171 | 3.64 | 1.33 | τCCCC (12) in ring |
| 15 | — | 192 | 185 | 1.1 | 0.55 | [δCNC (10) + τHCNC (14) + τHCCN (28)] in ring |
| 16 | — | 208 | 200 | 0.91 | 0.48 | [τHCCN (10) + τHCCN (22)] in ring |
| 17 | — | 218 | 210 | 3.5 | 0.74 | τCCCC (26) in ring |
| 18 | — | 237 | 228 | 1.85 | 5.13 | τCCCC (39) in ring |
| 19 | — | 276 | 266 | 1.97 | 1.12 | [δNCC (19) + τHCNC (14)] in ring |
| 20 | — | 289 | 278 | 3.39 | 3.47 | τCCCC (23) in ring + τC3C4N46N47 (10) + γNCCN in triazole (24) |
| 21 | — | 312 | 300 | 0.1 | 0.57 | [δCNC (10) + δCCN (34)] in ring |
| 22 | — | 331 | 319 | 2.2 | 0.44 | [τCNNC (34) + γONNC (14) + γNCNC (10)] in triazole |
| 23 | — | 338 | 325 | 0.84 | 0.08 | [δCCC (58) + τHCCC (16)] in ring |
| 24 | — | 343 | 329 | 13.23 | 1.19 | [δOCN (10) + δNNC (11)] in triazole + [δNCC (16) + δCCN (15)] in ring |
| 25 | — | 401 | 385 | 0.67 | 0.91 | δCCN (14) + τCCCC (15) in ring + τC4C3N47N46 (19) |
| 26 | — | 423 | 406 | 27.5 | 1.79 | [δOCN (20)] in triazole + τHCCC (16) in ring |
| 27 | — | 423 | 407 | 0.05 | 0.07 | τHCCC (12) in ring |
| 28 | — | 438 | 421 | 1.83 | 1.59 | [δCNC (10) + τCCCC (19)] in ring |
| 29 | — | 448 | 430 | 6.63 | 0.63 | [δCNC(15) + τCCCC (24)] in ring |
| 30 | — | 471 | 453 | 16.99 | 0.92 | [δCCN (26) + τCCCC (12)] in ring |
| 31 | — | 492 | 473 | 2.5 | 3.03 | [τCCCC (31) + γCCCC (21)] in ring |
| 32 | — | 519 | 499 | 2.12 | 0.25 | [δNCC (12) + δCNC (23) + τCCN(13)] in ring |
| 33 | — | 548 | 527 | 27.07 | 0.89 | δCNC (13) + γNCCC (13) in ring |
| 34 | — | 562 | 540 | 89.01 | 2.22 | τHNNC (41) in triazole |
| 35 | — | 566 | 544 | 42.94 | 1.04 | τHNNC (43) in triazole + γNCCC (12) in ring |
| 36 | — | 571 | 549 | 34.49 | 5.87 | δOCN (16) in triazole + δCCC (15) in ring |
| 37 | — | 622 | 598 | 16.52 | 3.16 | [δOCN (12) + δCNN (11) in triazole] + δCCC (19) in ring |
| 38 | — | 651 | 626 | 4.01 | 1.57 | δCCC (10) in ring + γN46C14N45C1 (24) |
| 39 | — | 657 | 631 | 3.99 | 4.84 | δCCC(27) in ring + γN46C14N45C1 (12) |
| 40 | 683 m | 669 | 643 | 0.51 | 11.57 | [νCC (10) + δCCC (56)] in ring |
| 41 | — | 684 | 657 | 18.2 | 4.53 | νNC (14) in ring |
| 42 | — | 720 | 692 | 12.35 | 0.38 | [τCNNC (12) + γONNC (67)] in triazole |
| 43 | — | 721 | 693 | 1.15 | 20.9 | τCCCC(43) in ring |
| 44 | 770 s | 730 | 702 | 82.6 | 12.16 | τHCCC (69) in ring |
| 45 | — | 757 | 727 | 2.5 | 1.79 | [τHCCC (10) + τCCCC (13) + γCCCC (23)] in ring + γN48C6C8C7 (31) |
| 46 | — | 779 | 749 | 3.06 | 8.71 | δHNC (19) in triazole + τHCCC (13) in ring |
| 47 | — | 792 | 762 | 2.44 | 6.3 | [νNC (14) + νNN (17) + δCNN (22)] in triazole |
| 48 | — | 810 | 778 | 5.52 | 1.83 | τHCCN (48) |
| 49 | — | 812 | 780 | 27.02 | 8.74 | τHCNC (22) in ring |
| 50 | — | 818 | 786 | 13.36 | 9.38 | νCC (15) in ring |
| 51 | 817 m | 834 | 802 | 3.72 | 0.88 | τHCCC (91) in ring |
| 52 | — | 852 | 819 | 12.19 | 23.25 | νCC (10) in ring |
| 53 | — | 855 | 822 | 59.95 | 0.59 | τHCCC (74) in ring |
| 54 | — | 874 | 840 | 0.02 | 1.37 | τHCCC (53) in ring |
| 55 | — | 888 | 854 | 7.14 | 19.56 | νCC (31) in ring + δC4C3N47 (14) |
| 56 | — | 919 | 883 | 0.34 | 12.81 | νCC (19) in ring |
| 57 | — | 931 | 895 | 0.58 | 7.64 | νCC (66) in ring |
| 58 | — | 948 | 911 | 0.29 | 0.75 | [δHCC (30) + τHCCC (30)] in ring |
| 59 | — | 953 | 916 | 2.64 | 2.06 | τHCCC (55) in ring |
| 60 | — | 981 | 943 | 0.31 | 0.57 | τHCCC (73) in ring |
| 61 | — | 998 | 960 | 0.03 | 0.02 | [τHCCC (16) + τCCCC (22)] in ring |
| 62 | — | 1,003 | 964 | 0.09 | 0.89 | τHCCC (55) in ring |
| 63 | — | 1,022 | 983 | 48.56 | 20.17 | νCC (14) in ring + δN44N45C1 (24) |
| 64 | — | 1,026 | 987 | 0.07 | 1.23 | [τHCCC (63) + τCCCC (21)] in ring |
| 65 | — | 1,028 | 988 | 46.32 | 31.8 | νNC (23) + νCC (50) in ring |
| 66 | — | 1,032 | 992 | 8.37 | 1.06 | δCCC(30) in ring |
| 67 | — | 1,035 | 995 | 16.31 | 29.27 | [νCC (28) + δCCC (31)] in ring |
| 68 | — | 1,055 | 1,014 | 15.8 | 9.8 | τH22C3N47N46 (80) |
| 69 | — | 1,056 | 1,015 | 27.69 | 61.75 | [νNC(17) + νNN (50)] in triazole |
| 70 | — | 1,059 | 1,018 | 13.81 | 1.77 | [δCCC(44) + δHCC (11)] in ring |
| 71 | — | 1,096 | 1,054 | 5.45 | 5.93 | νN48C10 (14) + νCC(28) + τHCCN (13) + τHCNC (13) in ring |
| 72 | — | 1,115 | 1,072 | 6.72 | 0.28 | [νCC (36) + δHCC (22)] in ring |
| 73 | — | 1,123 | 1,080 | 40.49 | 18.94 | [νCC (10), τHCNC (33)] in ring |
| 74 | — | 1,134 | 1,090 | 27.68 | 1.02 | [νNC(24) + τCCN (12) + τHCCN (17)] in ring |
| 75 | — | 1,165 | 1,120 | 5.94 | 56.46 | [δNCC (13) + δHCC(28)] in ring |
| 76 | — | 1,192 | 1,146 | 36.67 | 311.39 | νN44C2 (33) |
| 77 | — | 1,201 | 1,154 | 43.8 | 6.76 | δH24C6C5 (24) + νN44C2 (10) |
| 78 | — | 1,211 | 1,164 | 0.03 | 3.32 | δHCC (66) in ring |
| 79 | — | 1,226 | 1,178 | 0.83 | 9.66 | [νCC (21) + δHCC (55)] in ring |
| 80 | — | 1,234 | 1,186 | 71.33 | 326.11 | [νCC (10) + δHCC (22)] in ring |
| 81 | — | 1,236 | 1,188 | 0.13 | 5.03 | [νC15C20 (10) + δHCC (64)] in ring |
| 82 | — | 1,237 | 1,190 | 105.64 | 300.71 | [νNC (13) + δHCC (39)] in ring |
| 83 | — | 1,243 | 1,195 | 2.56 | 28.79 | [νCC (37) + δHCC (10)] in ring |
| 84 | — | 1,253 | 1,205 | 91.07 | 354.63 | [νNC (12) + νNN (11) + δCNN (25)] in triazole |
| 85 | — | 1,292 | 1,242 | 20.77 | 61.65 | [νC5C4 (25) + δHCC (12)] in ring |
| 86 | — | 1,318 | 1,267 | 374.3 | 6.12 | [νNC (14) + δHCC(21)] in ring |
| 87 | — | 1,324 | 1,273 | 105.76 | 7.28 | [νCC (12) + τHCCC(12)] in ring, [νNC (11) + δHCN (11)] in triazole |
| 88 | — | 1,336 | 1,284 | 32.9 | 35.99 | [νCC (11) + δHCC (31)] in ring |
| 89 | — | 1,346 | 1,294 | 0.11 | 2.29 | [νCC (68) + δHCC (25)] in ring |
| 90 | — | 1,365 | 1,313 | 32.89 | 62.97 | νCC (26) in ring |
| 91 | — | 1,383 | 1,329 | 9.39 | 32.25 | δHCC (56) in ring |
| 92 | — | 1,390 | 1,336 | 69.43 | 13.29 | νO49C2 (12) + δH21N44N45 (70) |
| 93 | — | 1,392 | 1,338 | 0.5 | 0.28 | δHCC (76) in ring |
| 94 | — | 1,403 | 1,348 | 241.89 | 85.33 | [δHCC (10) + τHCCN (37)] in ring |
| 95 | — | 1,405 | 1,351 | 33.5 | 13.3 | τHCNC (60) in ring |
| 96 | — | 1,418 | 1,363 | 65.64 | 245.01 | [νCC (12) + τHCCC (26)] in ring + δH22C3N47 (27) |
| 97 | — | 1,444 | 1,388 | 9.98 | 4.22 | wCH2 (58) |
| 98 | — | 1,448 | 1,392 | 39.03 | 79.94 | [νNC (12) + δHCC (27) + wCH2 (25)] in ring |
| 99 | — | 1,452 | 1,396 | 24.96 | 4.4 | wCH2 (68) |
| 100 | — | 1,464 | 1,464 | 130.25 | 118.62 | δH22C3N47 (28) |
| 101 | — | 1,476 | 1,419 | 13.97 | 311.77 | νCC (36) in ring |
| 102 | — | 1,502 | 1,444 | 5.95 | 0.73 | [νCC (24) + δHCC (42)] in ring |
| 103 | — | 1,510 | 1,452 | 40.87 | 36.86 | δH38C14H37 (89) |
| 104 | — | 1,528 | 1,469 | 3.02 | 11.22 | wCH2 (50) |
| 105 | — | 1,535 | 1,475 | 6.85 | 32.45 | wCH2 (50) |
| 106 | — | 1,536 | 1,476 | 0.95 | 21.54 | wCH2 (70) |
| 107 | — | 1,544 | 1,484 | 6.44 | 30.09 | wCH2 (32) |
| 108 | — | 1,546 | 1,486 | 14.55 | 0.27 | [νCC (11) + δHCC (56)] in ring |
| 109 | — | 1,548 | 1,489 | 6.15 | 3.46 | wCH2 (79) |
| 110 | — | 1,562 | 1,501 | 37.35 | 50.41 | wCH2 (43) |
| 111 | 1,588 s | 1,569 | 1,508 | 172.28 | 3.64 | [νN48C7 (11) + δHCC (13)] in ring |
| 112 | — | 1,577 | 1,516 | 16.01 | 1167.3 | [νCC (40) + δCCC (12)] in ring |
| 113 | — | 1,604 | 1,542 | 85.19 | 29.59 | νNC (56) in triazole + τHCCC (10) in ring |
| 114 | 1,610 s | 1,618 | 1,555 | 166.72 | 4836.81 | νNC (38) in triazole + δH22C3N47 (14) |
| 115 | — | 1,627 | 1,564 | 1.17 | 10.38 | [νCC (59) + δCCC (11)] in ring |
| 116 | — | 1,649 | 1,585 | 14.41 | 51.36 | νCC (47) in ring |
| 117 | — | 1,654 | 1,590 | 323.29 | 361.6 | νCC(48) in ring |
| 118 | 1,700 s | 1,703 | 1,637 | 400.78 | 61.51 | [νOC (61) + νNC (13)] in triazole |
| 119 | — | 3,019 | 2,902 | 6.17 | 48.4 | νsCH2 (23) + νsCH3 (46) |
| 120 | — | 3,021 | 2,904 | 49.47 | 148.84 | νsCH2(65) + νsCH2 (22) |
| 121 | — | 3,024 | 2,907 | 35.45 | 58.28 | νsCH2(49) + νsCH3 (36) |
| 122 | — | 3,028 | 2,911 | 83.38 | 324.07 | vsCH2 (31) + vsCH3(49) |
| 123 | — | 3,029 | 2,911 | 10.22 | 125.72 | vasCH2 (99) |
| 124 | — | 3,057 | 2,939 | 4.99 | 38.13 | vasCH2 (80) + vasCH2 (99) |
| 125 | — | 3,057 | 2,939 | 2.23 | 24.96 | vasCH2 (85) |
| 126 | — | 3,068 | 2,949 | 30.01 | 221.3 | νasCH3 (47) + νasCH2 (44) |
| 127 | — | 3,088 | 2,969 | 63.93 | 168.86 | νasCH3 (60) + νasCH2 (28) |
| 128 | — | 3,092 | 2,972 | 51.26 | 70.1 | νasCH3 (12) + νasCH2 (56) |
| 129 | — | 3,105 | 2,984 | 9.55 | 8.82 | νasCH3(93) |
| 130 | — | 3,110 | 2,990 | 83.41 | 32.77 | νasCH3 (50) + νasCH2 (28) |
| 131 | — | 3,153 | 3,031 | 0.87 | 21.44 | νC3H22(96) in triazole |
| 132 | — | 3,156 | 3,034 | 9.31 | 9.07 | νCH (97) in ring |
| 133 | — | 3,159 | 3,037 | 2.46 | 108.51 | νCH (94) in ring |
| 134 | 3,054 s | 3,163 | 3,041 | 12 | 73.76 | νCH (100) in ring |
| 135 | — | 3,170 | 3,048 | 21.79 | 111.29 | νCH (67) in ring |
| 136 | — | 3,181 | 3,058 | 55.42 | 42.72 | νCH (94) in ring |
| 137 | — | 3,191 | 3,067 | 4.44 | 32.65 | νCH (94) in ring |
| 138 | — | 3,195 | 3,071 | 30.53 | 374.28 | νCH (86) in ring |
| 139 | — | 3,215 | 3,090 | 24.59 | 33.59 | νCH (95) in ring |
| 140 | — | 3,217 | 3,093 | 21.07 | 165.95 | νCH (97) in ring |
| 141 | 3,165 m | 3,717 | 3,574 | 89.44 | 219.64 | vNH (100) |
ν, stretching; δ, bending; γ, out-of-plane bending; τ, torsion; s, strong; m, medium; w, weak; v, very. IR intensities (km mol−1); SR, Raman scattering activities (Å4 amu−1).
aThe experimental frequency values have been taken from ref. [17].
IR spectra simulated for DBT with DFT/B3LYP/6-311G level.
The correlation graph of IR wavenumbers for DBT.
3.2.1 NH and CH vibrations
The NH stretching mode for DBT was found at 3,165 cm−1 in the experimental IR spectral data [17]. The NH stretching vibration mode for DBT in our calculation was 3,574 cm−1 at B3LYP/6-311G level. Moreover, the NH in-plane bending vibration modes were recorded at 1,351, 1,336, and 1,146 cm−1 for DBT. Likewise, for DBT, the NH out-of-plane bending vibration modes existed at 540 and 319 cm−1.
In aromatic compounds, the C–H stretching vibration modes emerged above 3,000 cm−1 [47,48,49]. The aromatic C–H stretching vibration modes were noted at 3,034, 3,037, 3,041, 3,040, 3,058, 3,067, 3,071, 3,090, and 3,093 cm−1. Moreover, the modes that were found as combined with other vibrational ones at 1,338, 1,291, and 1,164 cm−1 for DBT resulted from C–H in-plane bending vibration modes and the modes found at 987, 964, 943, 895, 822, and 802 cm−1 for DBT were caused by C–H out of plane bending vibration modes. Calculated wavenumber values and assignments of DBT for C–H stretching, in-plane and out-plane bending modes, and other vibration modes are shown in Table 2.
3.2.2 CH2 and CH3 vibrations
The C–H stretching vibration modes for the aliphatic ═C–H group produced from sp2 hybrid were not observed [50,51,52]. From Table 2, it could be observed that the bands at 2,990, 2,982, 2,972, 2,969, 2,949, 2,939, 2,911, 2,907, 2,904, and 2,902 cm−1 resulted from the CH2 and CH3 symmetric and asymmetric stretching vibration modes for DBT. Additionally, the observed modes at 1,516, 1,501, and 1,489 cm−1 could be attributed to scissoring modes in the CH2 and CH3 groups. Moreover, symmetry bending modes of the CH2 and CH3 groups may be assigned to the observed modes at 1,484, 1,476, 1,475, 1,469, and 1,396 cm−1 for compound DBT. Similarly, rocking modes of CH2 and CH3 groups of DBT were recorded at 1,242, 1,164, and 1,072 cm−1. The computed vibrational modes in Table 2 were found to be consistent with the experimental ones.
3.2.3 CC, CN, and NN vibrations
The vibrational CC stretching bands in aromatic rings were reported at 1,627, 1,516, 1,486, and 1,313 cm−1, and the bands at 1,018, 995, 643, 631, and 626 cm−1 could be attributed to the vibrational CCC in-plane modes.
The C═N stretching vibration modes in 1,2,4-triazole and ring were recorded at 1,610 and 1,588 cm−1 in IR for DBT; the computed wavenumbers were 1,555 and 1,508 cm−1. The recorded bands at 1,273, 1,146, 1,015, 988, and 657 cm−1 could be explained with CN stretching vibration modes in the 1,2,4-triazole ring. The detected bands at 1,205, 1,015, and 762 cm−1, on the other hand, could be related to the NN stretching vibrational mode combined with others.
3.2.4 CO vibrations
The stretching C═O vibration modes usually appear as a strong peak in the mid-transition area at 870–1,540 cm−1 [51,52,53]. In this area, the position of the C═O stretching mode depends on the electronic/mass effects and physical situation of the surrounding substitutes, intermolecular and intramolecular hydrogen bonding as well as conjugations [50,51,52,53,54]. Thus, the peak at 1,700 cm−1 could be allocated to the C═O vibration mode in the triazole ring from Table 2, while the recorded band was 1,637 cm−1 [17]. In this respect, the band showing the CO stretching vibration of the studied molecule was found at 1,336 cm−1. Furthermore, the computed values at 692, 598, 549, 400, and 329 cm−1 could be referred to as the CO bending modes.
3.3 13C and 1H NMR isotropic chemical shift analysis
The isotropic chemical shift analysis in NMR spectroscopy enables us to classify relative ionic species and measure reliable magnetic properties that provide precise predictions of molecular geometries [55,56,57,58]. In this respect, the compound’s optimized molecular geometries were obtained with the B3LYP/6-311G level utilizing the IEFPCM solvent model in CCl4 (ε = 2.2), chloroform (ε = 4.9), and DMSO (ε = 46.7). The 1H and 13C NMR chemical shift values were computed at the same level using the GIAO and CSGT approaches, based upon the compound’s optimized molecular geometries. The experimentally obtained and computed chemical shifts of the mentioned molecule are presented in Table 3. In comparing the computed 1H and 13C NMR chemical shift values with the experimental ones, we presented the linear correlation graphics of the compound by presenting the results given in Table 3. Accordingly, the values (R 2) for 13C NMR chemical shift values of DBT in various solvents (DMSO, carbon tetrachloride, and chloroform) were found to be 0.9977 (DMSO), 0.9978 (CCl4), and 0.9978 (CHCl3) with the GIAO approach and 0.9937 (DMSO), 0.9940 (CCl4), and 0.9939 (CHCl3) with the CSGT approach, respectively. Furthermore, the values (R 2) for 1H NMR chemical shift values were recorded to be 0.8939 (DMSO), 0.8893 (CCl4), and 0.8882 (CHCl3) with the GIAO approach and 0.5827 (DMSO), 0.5830 (CCl4), and 0.5689 (CHCl3) with the CSGT approach, respectively (Figure 5).
The calculated and experimental 13C and 1H NMR isotropic chemical shifts for DBT (with respect to TMS, all values in ppm)
| Nucleus | GIAO method | CSGT method | |||||
|---|---|---|---|---|---|---|---|
| δ exp. * | δ calc (DMSO) | δ calc (CCl4) | δ calc (Chloroform) | δ calc (DMSO) | δ calc (CCl4) | δ calc (Chloroform) | |
| 1-C | 150.53 | 154.07 | 152.94 | 153.47 | 154.21 | 153.39 | 153.77 |
| 2-C | 155.74 | 153.04 | 152.59 | 152.83 | 147.60 | 147.44 | 147.54 |
| 3-C | 152.18 | 150.52 | 150.29 | 150.42 | 154.32 | 154.22 | 154.29 |
| 7-C | 146.78 | 148.98 | 148.19 | 148.60 | 147.31 | 146.59 | 146.97 |
| 15-C | 136.68 | 135.37 | 135.20 | 135.26 | 136.12 | 135.84 | 135.96 |
| 5-C | 130.25 | 132.84 | 132.76 | 132.80 | 135.38 | 135.31 | 135.35 |
| 16-C | 129.46 | 129.56 | 129.54 | 129.56 | 131.07 | 131.11 | 131.10 |
| 20-C | 129.46 | 129.44 | 129.39 | 129.42 | 130.94 | 130.94 | 130.94 |
| 19-C | 129.09 | 127.41 | 127.00 | 127.18 | 130.27 | 129.93 | 130.08 |
| 17-C | 129.09 | 127.36 | 126.97 | 127.14 | 130.24 | 129.91 | 130.05 |
| 18-C | 127.34 | 126.12 | 125.70 | 125.89 | 129.08 | 128.74 | 128.89 |
| 9-C | 130.25 | 123.94 | 124.51 | 124.24 | 124.55 | 124.98 | 124.77 |
| 4-C | 120.16 | 119.80 | 121.08 | 120.44 | 121.39 | 122.54 | 121.97 |
| 8-C | 111.70 | 109.70 | 109.14 | 109.40 | 113.13 | 112.67 | 112.89 |
| 6-C | 111.70 | 108.45 | 107.92 | 108.18 | 112.48 | 111.98 | 112.23 |
| 12-C | 44.47 | 44.75 | 44.85 | 44.80 | 60.65 | 60.72 | 60.69 |
| 10-C | 44.47 | 44.71 | 44.81 | 44.77 | 60.62 | 60.68 | 60.65 |
| 14-C | 31.84 | 29.78 | 30.05 | 29.92 | 40.99 | 41.26 | 41.13 |
| 13-C | 13.05 | 7.95 | 8.20 | 8.08 | 28.74 | 28.98 | 28.86 |
| 11-C | 13.05 | 7.75 | 8.03 | 7.89 | 28.46 | 28.72 | 28.59 |
| 22-H | 9.35 | 9.33 | 9.39 | 9.36 | 7.84 | 7.90 | 7.87 |
| 26-H | 7.54 | 7.26 | 7.27 | 7.27 | 6.83 | 6.85 | 6.84 |
| 40-H | 7.28 | 6.55 | 6.42 | 6.48 | 6.44 | 6.33 | 6.38 |
| 42-H | 7.28 | 6.55 | 6.41 | 6.48 | 6.43 | 6.33 | 6.38 |
| 41-H | 7.20 | 6.48 | 6.34 | 6.40 | 6.30 | 6.20 | 6.24 |
| 39-H | 7.22 | 6.46 | 6.34 | 6.40 | 6.33 | 6.24 | 6.28 |
| 43-H | 7.22 | 6.45 | 6.32 | 6.38 | 6.30 | 6.21 | 6.25 |
| 21-H | 11.82 | 6.39 | 6.31 | 6.26 | 4.14 | 3.93 | 4.04 |
| 23-H | 7.54 | 6.38 | 6.13 | 6.34 | 6.04 | 6.00 | 6.02 |
| 25-H | 6.69 | 5.76 | 5.60 | 5.67 | 6.17 | 6.05 | 6.11 |
| 24-H | 6.69 | 5.73 | 5.58 | 5.65 | 6.12 | 6.00 | 6.06 |
| 37-H | 3.98 | 3.14 | 3.06 | 3.10 | 3.78 | 3.72 | 3.75 |
| 38-H | 3.98 | 3.14 | 3.06 | 3.10 | 3.77 | 3.72 | 3.74 |
| 28-H | 3.37 | 2.99 | 2.97 | 2.98 | 5.05 | 5.05 | 5.05 |
| 33-H | 3.37 | 2.96 | 2.94 | 2.95 | 5.07 | 5.07 | 5.07 |
| 27-H | 3.37 | 2.22 | 2.07 | 2.14 | 4.80 | 4.70 | 4.75 |
| 32-H | 3.37 | 2.22 | 2.07 | 2.14 | 4.79 | 4.70 | 4.74 |
| 31-H | 1.09 | 0.67 | 0.76 | 0.72 | 3.65 | 3.72 | 3.69 |
| 34-H | 1.09 | 0.57 | 0.67 | 0.63 | 3.62 | 3.69 | 3.66 |
| 35-H | 1.09 | 0.39 | 0.35 | 0.37 | 3.43 | 3.38 | 3.42 |
| 30-H | 1.09 | 0.37 | 0.33 | 0.35 | 3.41 | 2.67 | 3.39 |
| 29-H | 1.09 | 0.18 | 0.11 | 0.14 | 2.72 | 2.67 | 2.70 |
| 36-H | 1.09 | 0.16 | 0.09 | 0.12 | 2.74 | 2.69 | 2.71 |
*The experimental 13C and 1H NMR isotropic chemical shift values have been taken from ref. [17].
The correlation graphs for 13C and 1H NMR chemical shifts (a; in DMSO), (b; in CCl4), (c; CHCl3) with GIAO (1) and CSGT (2) methods for DBT.
Our data analysis showed that 13C NMR chemical shift values for the title molecule were significant, as predicted [57,58]. In Table 3, the 13C NMR chemical shift value of DBT was noted at 155.74 ppm for the C2 carbon atom double-bonded to the oxygen in a carbonyl group [17]. The computed ppm values for the C2 atom in CCl4 (ε = 2.2), chloroform (ε = 4.9), and DMSO (ε = 46.7) solvents were theoretically determined to be 153.04 (DMSO), 152.59 (CCl4), and 152.83 ppm (CHCl3) with the GIAO approach and 147.60 (DMSO), 147.44 (CCl4), and 147.54 ppm (CHCl3) with the CSGT approach, respectively. Based on the 13C NMR chemical shift values of the C1 carbon atom bound to electronegative nitrogen atoms in 1,2,4-triazole ring and C3 carbon atom with sp2 hybridized in imine group, we observed 150.53 and 152.18 ppm, respectively [17]. Likewise, the 13C-NMR chemical shift values for these carbon atoms (C1 and C3 bound to nitrogen atoms in the triazole ring) were recorded as 154.07 (DMSO), 152.94 (CCl4), and 153.47 ppm (CHCl3) with the GIAO approach and 154.21 (DMSO), 153.39 (CCl4), and 153.77 ppm (CHCl3) with the CSGT approach, respectively. Moreover, the 13C-NMR chemical shift values for these carbon atoms (C10 and C12) which bound to other nitrogen atoms in the compound were found to be 44.47 ppm, while these values of the carbons mentioned above in DMSO, CCl4, and chloroform were observed to be 60.65 (DMSO), 60.72 (CCl4), and 60.69 ppm (CHCl3) with the GIAO approach and 60.62 (DMSO), 60.68 (CCl4), and 60.65 ppm (CHCl3) with the CSGT approach, respectively. The carbon atoms in the aromatic ring were observed at the interval 111.70–146.78 ppm, while these values of the carbons mentioned above were reported at the interval 107–149 ppm.
On the other hand, the recorded 1H NMR chemical shifts at intervals 6.69 and 7.54 ppm may be allocated to the hydrogen atoms in the aromatic ring [42]. The 1H-NMR chemical shift values for the hydrogen atoms bound to the diethylamino group in the compound were found to be 1.09 and 3.37 ppm, while these computed values were observed at the interval 0.09–5.10 ppm.
The experimentally observed and theoretically computed shift values of all protons and carbon atoms in alkyl groups, triazole, and aromatic rings are presented in Table 3.
The computed and experimental values were found to be closely correlated (Figure 5);
δ exp(ppm) = 0.9780δ calc + 3.6122 (R 2 = 0.9977) (in DMSO for 13C-NMR/GIAO method)
δ exp(ppm) = 0.9827δ calc + 3.2340 (R 2 = 0.9978) (in CCl4 for 13C-NMR/GIAO method)
δ exp(ppm) = 0.9804δ calc + 3.4171 (R 2 = 0.9978) (in CHCl3 for 13C-NMR/GIAO method)
δ exp(ppm) = 1.397δ calc – 19.505 (R 2 = 0.9937) (in DMSO for 13C-NMR/CSGT method)
δ exp(ppm) = 1.145δ calc – 19.999 (R 2 = 0.9940) (in CCl4 for 13C-NMR/CSGT method)
δ exp(ppm) = 1.1424δ calc – 19.759 (R 2 = 0.9939) (in CHCl3 for 13C-NMR/CSGT method)
δ exp(ppm) = 1.0416δ calc + 0.7677 (R 2 = 0.8939) (in DMSO for 1H-NMR/GIAO method)
δ exp(ppm) = 1.0482δ calc + 0.8188 (R 2 = 0.8893) (in CCl4 for 1H-NMR/GIAO method)
δ exp(ppm) = 1.0434δ calc + 0.8011 (R 2 = 0.8882) (in CHCl3 for 1H-NMR/GIAO method)
δ exp(ppm) = 1.6233δ calc – 3.226 (R 2 = 0.5877) (in DMSO for 1H-NMR/CSGT method)
δ exp(ppm) = 1.5565δ calc – 2.7557 (R 2 = 0.5630) (in CCl4 for 1H-NMR/CSGT method)
δ exp(ppm) = 1.6091δ calc – 3.1072 (R 2 = 0.5689) (in CHCl3 for 1H-NMR/CSGT method).
3.4 UV-vis spectroscopy and HOMO–LUMO analyses
The compound’s experimental absorption wavelength values were found to be 358 and 216 nm in ethanol solvent. The absorption wavelengths (λ), oscillator strengths (ƒ), and excitation energies of the UV-vis absorption spectra for DBT were determined utilizing TD-DFT/B3LYP methods with 6-311G level in various solvents (in chloroform [ε = 4.9], ethanol [ε = 24.55], and water [ε = 78.39]). The theoretical absorption wavelengths of DBT were 352.54, 287.01, and 277.00 nm in the chloroform/353.88, 287.74, and 278.74 nm in the ethanol solvent/353.85, 287.86, and 275.52 nm in water. The computed and experimentally observed UV parameters and simulated spectra of DBT are shown in Table 4 and Figure 6. The experimental and computed absorption wavelength (λ) values were found to be significantly correlated:
The experimental and calculated absorption wavelength (λ), excitation energies, and oscillator strengths (ƒ) for DBT
| Exp.* (in ethanol) | Transition | The calculated with B3LYP/6-311G level in CHCl3/Ethanol/Water | ||
|---|---|---|---|---|
| λ (nm)/ε (L mol−1 cm−1) | λ max (nm) | Excitation energy (eV) | ƒ (oscillator strength) | |
| 358 (17,280) |
|
352.54/353.88/353.85 | 3.5169/3.5035/3.5039 | 1.0433/1.0223/1.0156 |
|
|
287.01/287.74/287.86 | 4.3199/4.3089/4.3070 | 0.0573/0.0562/0.0558 | |
| 209 (19,526) |
|
277.00/278.74/275.52 | 4.4760/4.4964/4.5001 | 0.0097/0.0128/0.0134 |
*The experimental absorption wavelength (λ) values have been taken from ref. [17].
UV-Vis spectra simulated with DFT/B3LYP/6-311G level in solvent phases for DBT.
λ exp(nm) = 1.9725λ calc – 337.37 (R 2 = 1.000) (in CHCl3)
λ exp(nm) = 1.9830λ calc – 343.73 (R 2 = 1.000) (in ethanol)
λ exp(nm) = 1.9022λ calc – 315.10 (R 2 = 1.000) (in water).
It has been well acknowledged that the HOMO means the electron-filled outermost orbital and functions as an electron donor, and the LUMO is the first unoccupied innermost orbital to be unfilled by electron and acts as an electron acceptor which is called frontier molecular orbitals. Thus, the energy of the HOMO which is mainly related to the ionization potential defines the ability of electron-donating. In contrast, LUMO’s energy has generally been related to the electron affinity and demonstrates electron-reception/electron-absorption capacity. Molecular chemical stability is indicated by the generated energy gap between HOMO and LUMO and is a critical parameter for determining the properties of molecular electrical transport [59]. The connections between the chemical reactivity, stability, polarizability, chemical hardness-softness, and electronegativity of a molecule can be computed through HOMO and LUMO energy values [60]. The energy differences between HOMOs–LUMOs, electronegativity, and chemical hardness results of DBT are presented in Table 5, and the 3D representations of their HOMOs and LUMOs are displayed in Figure 7.
The calculated HOMO-1, HOMO, LUMO, and LUMO+1 energies, energy gap, electronegativity, and chemical hardness values for DBT
| Parameters | B3LYP/6-311G |
|---|---|
| EHOMO-1 (eV) | −6.329 |
| EHOMO (eV) | −5.323 |
| ELUMO (eV) | −1.408 |
| ELUMO+1 (eV) | −0.273 |
| EHOMO – ELUMO (eV) | 3.920 |
| EHOMO – ELUMO+1 (eV) | 5.056 |
| EHOMO-1 – ELUMO (eV) | 4.921 |
| EHOMO-1 – ELUMO+1 (eV) | 6.056 |
| χ (Electronegativity) (eV) | 3.366 |
| η (Chemical hardness) (eV) | 1.957 |
The calculated HOMO-1, HOMO, LUMO, and LUMO+1 energy values, energy gap values for DBT.
3.5 MEP
MEPs are used to determine the interaction between molecules, which have recently been used to interpret and predict relative sites of reactivity for the nucleophilic and electrophilic attack, to examine biological identification, interactions with hydrogen bonding, molecular cluster, zeolite, and crystal behavior studies, and to compare and predict a broad range of macroscopic properties [61]. In addition, MEP defines the molecule’s overall charge distribution; it demonstrates the similarities between the molecular properties such as dipole moments, partial charges, chemical reactivity, and electronegativity. The electrostatic potential on the surface is represented by different colors in our study (Figure 8). Thus, red regions indicate negative potential, and blue regions indicate positive potential. In addition, the green color sections reflect zero potential areas. The negative potentials were associated with the electrophilic attack, while the positive ones were associated with the nucleophilic attack. MEPs for the title molecule based on optimized molecular structure were determined by using B3LYP/6-311G level, and 3D plots of MEPs are presented in Figure 8. The MEP map’s negative regions were primarily located on the carbonyl oxygen atom (O49) and the nitrogen atom (N45) in the triazole ring due to their electronegative properties. The MEP map’s positive region was located on the hydrogen atom bound to the nitrogen atom in the triazole ring representing the potential sites for nucleophilic attack. These sites included some knowledge of non-covalent molecular interaction regions.
The MEP map for DBT.
3.6 NLO properties
The significance of NLO features for molecular systems is contingent upon the efficacy of electrical communication between the donating and withdrawing groups involved in intramolecular charge transfer. NLO properties originate from electromagnetic field interactions in different media to generate new fields changing in terms of phase, frequency, amplitude, or other propagation properties from the incident fields [62]. Organic molecules with substantial NLO behavior usually have a π-electron conjugated moiety replaced through an electron donor group on one end of the conjugated structure and an electron receptor group on the other, forming a “push–pull” conjugated structure [63]. Numerous research groups have examined the compatibility of practical and theoretical methodologies for the construction and characterization of highly efficient NLO materials [64,65,66,67]. We investigated the linear polarizability (α), first hyperpolarizability (β) of DBT to offer a critical overview of the NLO parameters and to evaluate using the DFT model (B3LYP) in the gas phase. The linear polarizability (α), first hyperpolarizability (β), and total static dipole moment (µ) for DBT were described utilizing x, y, and z components as [68]:
The linear polarizability (α), first hyperpolarizability (β), and total static dipole moment (µ) of DBT were computed at the B3LYP/6-311G level. The computed polarizability (α), first hyperpolarizability (β), and total dipole moment (µ) for the mentioned compound were observed to be 42.6093 × 10−24 cm5 esu−1, 10.9054 × 10−30 cm5 esu−1, and 5.1375 D, respectively (Table 6). In this vein, urea is one of the essential molecules used to determine molecular systems’ NLO properties. The computed
The total energy (Hartree), the electric dipole moment μ (Debye), the average polarizability α total (10−24 cm5 esu−1), and first hyperpolarizability β total (10−30 cm5 esu−1) for DBT
| Urea | B3LYP | |
|---|---|---|
| E | −1124.8716 | |
| μ x | −4.4673 | |
| μ y | −2.5257 | |
| μ z | 0.2412 | |
| μ | 1.3197 | 5.1375 |
| α xx | 451.3983 | |
| α xy | 13.8852 | |
| α yy | 244.0924 | |
| α xz | 4.2412 | |
| α yz | 2.2514 | |
| α zz | 167.0458 | |
| α | 42.6093 | |
| Δ α (esu) | 37.7500 | |
| β xxx | 773.3342 | |
| β xxy | 1248.6634 | |
| β xyy | 246.5077 | |
| β yyy | −269.2251 | |
| β xxz | 84.7340 | |
| β xyz | 20.6039 | |
| β yyz | 0.2402 | |
| β xzz | −89.7842 | |
| β yzz | −70.6770 | |
| β zzz | −1.2540 | |
| β | 0.1974 | 10.9054 |
3.7 Atomic charges and thermodynamic properties
The computed Mulliken atomic charges and thermodynamic parameters for DBT through B3LYP/6-311G level in the gas phase are reported in Table 7 and Figure 9 [70]. The electronegative N44, N45, N46, N47, N48, and O49 atoms in DBT had negative atomic charge values. The charge values of all those electronegative atoms mentioned above were determined to be as –0.6099 (N44), –0.1644 (N45), –0.6542 (N46), –0.1681 (N47), –0.6408 (N48), and –0.4204 (O49) a.u. The carbon atoms (C1, C2, and C7) bonded to electronegative atoms in DBT had positive atomic charge values. The charge values of all the above-mentioned carbon atoms were recorded to be 0.5431 (C1), 0.7695 (C2), and 0.3900 (C7) a.u. The C2 atom surrounded by three electronegative atoms (N44, N46, and O49), the C1 atom surrounded by two electronegative atoms (N45 and N46), and the C7 atom surrounded by one electronegative atom (N48) had the highest positive charge values. The other carbon atoms of DBT had, on the other hand, positive/negative charge values. In addition, all charge values of the hydrogen atoms in the DBT compound were positive.
The computed Mulliken atomic charges for DBT
| Atoms | Mulliken atomic charges | Atoms | Mulliken atomic charges |
|---|---|---|---|
| 1C | 0.5431 | 26H | 0.1664 |
| 2C | 0.7695 | 27H | 0.1746 |
| 3C | −0.0246 | 28H | 0.1956 |
| 4C | −0.0575 | 29H | 0.1776 |
| 5C | −0.1530 | 30H | 0.1805 |
| 6C | −0.2113 | 31H | 0.1988 |
| 7C | 0.3900 | 32H | 0.1751 |
| 8C | −0.2131 | 33H | 0.1900 |
| 9C | −0.0766 | 34H | 0.1968 |
| 10C | −0.2228 | 35H | 0.1844 |
| 11C | −0.4900 | 36H | 0.1683 |
| 12C | −0.2204 | 37H | 0.2242 |
| 13C | −0.4903 | 38H | 0.2183 |
| 14C | −0.5570 | 39H | 0.1565 |
| 15C | 0.0304 | 40H | 0.1507 |
| 16C | −0.1005 | 41H | 0.1463 |
| 17C | −0.1605 | 42H | 0.1413 |
| 18C | −0.1326 | 43H | 0.1478 |
| 19C | −0.1613 | 44N | −0.6099 |
| 20C | −0.1044 | 45N | −0.1644 |
| 21H | 0.3684 | 46N | −0.6542 |
| 22H | 0.2396 | 47N | −0.1681 |
| 23H | 0.1649 | 48N | −0.6408 |
| 24H | 0.1711 | 49O | −0.4204 |
| 25H | 0.1633 |
Mulliken atomic charge graph for DBT.
Many thermodynamic functions, including entropy
Correlation graph for DBT (a) entropy and temperature, (b) heat capacity and temperature, and (c) enthalpy and temperature.
The computed thermodynamic functions at different temperatures for DBT
| T (°K) |
|
|
|
|---|---|---|---|
| 100 | 107.969 | 37.92 | 257.794 |
| 200 | 143.332 | 63.368 | 262.842 |
| 298.15 | 174.496 | 90.913 | 270.398 |
| 300 | 175.073 | 91.443 | 270.567 |
| 400 | 205.815 | 119.248 | 281.121 |
| 500 | 235.558 | 143.555 | 294.296 |
| 600 | 263.931 | 163.655 | 309.690 |
| 700 | 290.743 | 180.121 | 326.906 |
| 800 | 315.976 | 193.722 | 345.619 |
| 900 | 339.703 | 205.085 | 365.576 |
| 1,000 | 362.03 | 214.671 | 386.577 |
These values showed that thermodynamic parameters including entropy
4 Conclusion
The chemical structure, vibrational frequencies, UV-vis spectroscopy, proton and carbon NMR chemical changes, HOMO and LUMO studies, thermodynamic, NLO, and molecular electronic properties for DBT were all determined by utilizing from Density Functional Theory/B3LYP method and 6-311G level. The theoretical results (DFT/B3LYP) were found to be consistent with the experimental ones based upon the optimized structure analysis. By evaluating the results of the experimental work [17], it was determined that the theoretical vibrational frequencies, 1H and 13C-NMR chemical shift values and UV spectra fit the experimental data very well. The NLO functions of DBT were determined, which revealed that it could provide the basis for the future design of efficient NLO materials. Based upon the MEP surface, the compound’s most reactive site for the electrophilic attack was found to be around the nitrogen and oxygen atoms, whereas the most reactive region for the nucleophilic attack was realized to be around the NH in the triazole ring. We used HOMO–LUMO energy values for DBT to calculate parameters like the HOMO–LUMO energy gap, electronegativity, and chemical hardness values. It was observed that DBT had good stability and high chemical hardness. The linear polarizability (α), the first hyperpolarizability (β), and dipole moment (µ) were calculated, and the results showed that it could provide the basis for the future design of efficient NLO materials. The findings revealed that the entropies, enthalpies, and heat capacities went up as temperature rose due to intensities of the molecular vibrations rising as a consequence of increasing temperature.
Acknowledgments
The numerical calculations reported in this study were entirely performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA resources).
-
Funding information: The authors state no funding involved.
-
Author contributions: Hilal Medetalibeyoğlu wrote the manuscript and supervised the project. Haydar Yüksek interpreted the spectral data.
-
Conflict of interest: The authors state no conflict of interest.
-
Code availability: ChemDraw Ultra 8.0, Gaussian 0.9, GaussView 5.0, Veda 4, Chemcraft 1.8.
-
Data availability statement: The datasets generated during and/or analyzed during this study are available from the corresponding author on reasonable request.
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