Introduction

Pyrazolines are one of the most important five-membered heterocycles that have received lots of attention in organic synthesis [1,2,3,4]. Due to the presence of dihydro pyrazoles in their chemical structures as a central core in all derivatives they possess a wide spectrum of biological activities such as anticancer, anti-inflammatory, antiviral and antibacterial activities [5,6,7,8,9]. Especially, 1,3,5-Triaryle-2-pyrazolines, are used widely in fluorescent dyes due to their emitting vivid blue fluorescence with prominent and high fluorescence quantum yield [10,11,12,13,14,15,16]. Moreover, intermolecular charge transfer (ICT) is attracting phenomenon that is typically achieved for pyrazoline derivatives [17]. With great progress industrially pyrazolines are used as brightening agents in textile manufacture, paper and plastic fabrication [18,19,20,21,22,23].

In the present work, we reported the synthesis of twenty-one novel 1,3,5-triaryl-2-pyrazolines as mention in details on our previous work [24]. Then we select four synthesized active novel pyrazolines and named with 13, 15, 18 and 23 due to their prominent fluorescence quantum yield (0.819, 0.858, 0.553, 0.844) than quinine sulfate (reference).

The density functional theory (DFT) calculations are applied for the selected (13,15,18 and 23) compounds. All the experimental investigations observed data were compared with theoretical computations obtained from DFT calculations.

Experimental

Instrumentation

The FT-IR spectra (KBr) were recorded on a shimadzu FT-IR 8400S spectrophotometer. UV-vis spectra were recorded on a shimadzu UV-1800 spectrophotometer. Emission spectra were measured on a LUMINA fluorescence spectrometer. 1H-NMR spectra were measured on a Varian Mercury 300 (300 MHz) and a Bruker Ascend 400/R (400 MHz) spectrometer. 13C-NMR spectra were recorded on a Bruker Ascend 400/R (100 MHz) spectrometer. Melting points were recorded on a Stuart SMP3 melting point apparatus.

Synthesis General Procedure

A mixture of equimolar amounts of the appropriate 1,3-diaryl-2-propen-1-ones 1–9 (5 mmol) and the corresponding aryl hydrazines 10–12 (the hydrochloride salt was used in case of 11 and 12) in absolute ethanol (15 ml) was boiled under reflux (TLC control). The solid separated upon storing the reaction mixture at room temperature overnight, was collected and crystallized from a suitable solvent affording the corresponding pyrazolines 13–33 (Scheme 1).

Scheme 1
scheme 1

The selected synthetic approach for 2-prazolines 13–33

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Experimental Characterization of the Selected Pyrazolines 13, 15, 18 and 23

The chemical structures of selected compounds 13, 15, 18 and 23 are given in Scheme 2. The details of synthesis procedures for selected four compounds are reported as viz.:

  • 3-(4-Chlorophenyl)-5-(4-fluorophenyl)-1-phenyl-4,5-dihydro-1 H -pyrazole (13)

    Obtained from reaction of 1 and 10. Reaction time 6 h, almost colorless microcrystals from n-butanol, mp 156–158 °C, yield 89% (1.55 g). IR ν (cm−1): 1589, 1558, 1504, 1493. 1H-NMR δ (ppm): (300 MHz) 3.08 (dd, J = 7.5, 17.1 Hz, 1H, upfield H of pyrazolinyl H2C-4), 3.81 (dd, J = 12.5, 17.0 Hz, 1H, downfield H of pyrazolinyl H2C-4), 5.28 (dd, J = 7.2, 12.3 Hz, 1H, pyrazolinyl HC-5), 6.78–6.85 (m, 1H, arom. H), 7.01–7.43 (m, 10H, arom. H), 7.65 (d, J = 8.7 Hz, 2H, arom. H). 13C-NMR δ (ppm): (100 MHz) 43.4 (pyrazolinyl H2C-4), 64.0 (pyrazolinyl HC-5), 113.5, 116.0, 116.2, 119.5, 125.3, 126.9, 127.1, 127.5, 127.6, 128.8, 128.9, 129.0, 129.1, 131.2, 134.4, 138.0, 138.1, 144.5, 145.6, 161.0, 163.4 (arom. C). Elemental analysis: C21H16ClFN2 required C, 71.90; H, 4.60; N, 7.99, found C, 72.09; H, 4.71; N, 8.07.

  • 5-(4-Fluorophenyl)- 3-(4-methylphenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (15)

    Obtained from reaction of 3 and 10. Reaction time 9 h, pale yellow microcrystals from n-butanol, mp 147–149 °C, yield 82% (1.35 g). IR ν (cm−1): 1597, 1551, 1497. 1H-NMR δ (ppm): (300 MHz) 2.39 (s, 3H, CH3), 3.10 (dd, J = 7.4, 17.0 Hz, 1H, upfield H of pyrazolinyl H2C-4), 3.83 (dd, J = 12.5, 17.0 Hz, 1H, downfield H of pyrazolinyl H2C-4), 5.24 (dd, J = 7.2, 12.3 Hz, 1H, pyrazolinyl HC-5), 6.79–7.64 (m, 13H, arom. H). 13C-NMR δ (ppm): (100 MHz) 21.4 (CH3), 43.7 (pyrazolinyl H2C-4), 63.8 (pyrazolinyl HC-5), 113.4, 115.9, 116.1, 119.2, 125.8, 127.5, 127.6, 129.0, 129.3, 129.9, 138.4, 138.5, 138.8, 144.9, 145.0, 160.9, 163.4 (arom. C). Elemental analysis: C22H19FN2 required C, 79.97; H, 5.80; N, 8.48, found C, 80.04; H, 5.92; N, 8.64.

  • 1-(4-Chlorophenyl)-5-(4-fluorophenyl)-3-(2-naphthyl)-4,5-dihydro-1H-pyrazole (18)

    Obtained from reaction of 6 and 11. Reaction time 8 h, pale yellow microcrystals from n-butanol, mp 184–186 °C, yield 80% (1.60 g). IR ν (cm−1): 1595, 1495, 1439. 1H-NMR δ (ppm): (400 MHz) 3.25 (dd, J = 7.0, 17.0 Hz, 1H, upfield H of pyrazolinyl H2C-4), 3.93 (dd, J = 12.3, 17.0 Hz, 1H, downfield H of pyrazolinyl H2C-4), 5.26 (dd, J = 7.0, 12.2 Hz, 1H, pyrazolinyl HC-5), 7.03–7.08 (m, 4H, arom. H), 7.16–7.19 (m, 2H, arom. H), 7.28–7.32 (m, 2H, arom. H), 7.50–7.53 (m, 2H, arom. H), 7.81–7.88 (m, 4H, arom. H), 8.17 (dd, J = 1.6, 8.6 Hz, 1H, arom. H). 13C-NMR δ (ppm): (100 MHz) 43.6 (pyrazolinyl H2C-4), 63.9 (pyrazolinyl HC-5), 114.6, 116.1, 116.3, 123.4, 124.2, 125.4, 126.4, 126.58, 126.59, 127.5, 127.6, 127.9, 128.1, 128.3, 128.9, 129.2, 130.0, 133.3, 133.6, 137.7, 137.8, 143.1, 147.4, 161.0, 163.5 (arom. C). Elemental analysis: C25H18ClFN2 required C, 74.90; H, 4.53; N, 6.99, found C, 75.12; H, 4.71; N, 7.18.

  • 5-(4-Fluorophenyl)-1-(4-methylphenyl)-3-(2-naphthyl)-4,5-dihydro-1H-pyrazole (23)

    Obtained from reaction of 6 and 12. Reaction time 6 h, pale yellow microcrystals from n-butanol, mp 188–189 °C, yield 84% (1.60 g). IR ν (cm−1): 1602, 1558, 1516, 1504. 1H-NMR δ (ppm): (400 MHz) 2.28 (s, 3H, CH3), 3.25 (dd, J = 7.4, 16.9 Hz, 1H, upfield H of pyrazolinyl H2C-4), 3.91–3.99 (m, 1H, downfield H of pyrazolinyl H2C-4), 5.27–5.32 (m, 1H, pyrazolinyl HC-5), 7.04–7.08 (m, 6H, arom. H), 7.28–7.36 (m, 2H, arom. H), 7.48–7.51 (m, 2H, arom. H), 7.81–7.88 (m, 4H, arom. H), 8.19 (d, J = 8.7 Hz, 1H, arom. H). 13C-NMR δ (ppm): (100 MHz) 20.5 (CH3), 43.5 (pyrazolinyl H2C-4), 64.2 (pyrazolinyl HC-5), 113.6, 115.9, 116.1, 123.5, 125.0, 125.4, 126.3, 126.5, 127.6, 127.7, 127.8, 128.1, 128.2, 128.7, 129.5, 129.7, 130.4, 133.3, 133.4, 138.39, 138.42, 142.5, 146.4, 160.9, 163.4 (arom. C). Elemental analysis: C26H21FN2 required C, 82.08; H, 5.56; N, 7.36, found C, 82.24; H, 5.67; N, 7.22.

Scheme 2
scheme 2

The chemical structures of (a) compound 13, (b) compound 15, (c) compound 18 and (d) compound 23

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Computational Details

All computations were performed with the Gaussian 09 W program package [25] with Gaussian View 6 molecular visualization program [26]. The hybrid Becke-3 function with Lee-Yang-Parr correlation function (B3LYP) method [27] of density functional theory (DFT) with 6-31G (d,p) basis set [28] in the gas phase was applied for prediction of molecular geometries and calculations of vibrational frequencies. For the molecular geometry optimization, no symmetry constraints were applied. The computed vibrational frequency values were scaled with a scaling factor 0.9613 and no imaginary frequencies were obtained from calculations. Time- dependent functional theory (TD-DFT) was performed to simulate the UV-vis spectra at B3LYP/6-31G (d,p) level of theory in the gas phase for the optimized structured at the ground state. The excited states at the same level of theory of TD-DFT were optimized to obtain the simulated emission spectra. 1H and 13C NMR computations were performed using the gauge-invariant atomic orbital (GIAO) method at B3LYP/6–311 + G(2d,p) in gas phase after the molecular geometry was optimized at the same level of theory. Furthermore, the dipole moment, energy of optimization, HOMO-LUMO analysis and molecular electrostatic potential (MEP) maps for selected compounds were calculated via DFT/B3LYP method using 6–31 G (d,p) basis set in the gas phase and their 3D plots were visualized at the same level of theory.

Optimized Molecular Geometries

For compounds 13, 15, 18 and 23, the optimized molecular structures are computed via DFT using B3LYP method and 6-31G (d,p) basis set, with the numbering of atoms, are presented in Figs. 1, 2, 3, and 4. The complete optimized molecular geometry parameters for candidate compounds are given in Tables (1S–4S). The selected optimized molecular geometry parameters for given compounds in the gas phase are presented in Tables 1, 2, 3, and 4.

Fig. 1
figure 1

The optimized molecular geometry of compound 13 at DFT (B3LYP) with 6–31 G(d, p) basis set in gas phase

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Fig. 2
figure 2

The optimized molecular geometry of compound 15 at DFT (B3LYP) with 6–31 G(d, p) basis set in gas phase

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Fig. 3
figure 3

The optimized molecular geometry of compound 18 at DFT (B3LYP) with 6–31 G(d, p) basis set in gas phase

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Fig. 4
figure 4

The optimized molecular geometry of compound 23 at DFT (B3LYP) with 6–31 G(d, p) basis set in gas phase

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Table 1 The selected bond distances, bond angles and dihedral angles for compound 13
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Table 2 The selected bond distances, bond angles and dihedral angles for compound 15
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Table 3 The selected bond distances, bond angles and dihedral angles for compound 18
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Table 4 The selected bond distances, bond angles and dihedral angles for compound 23
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As seen from the selected tables of optimized geometry parameters for compounds 13, 15, 18 and 23, the N-N bond lengths located in the core ring (pyrazoline ring), are 1.364, 1.369, 1.371 and 1.369 respectively, in excellent consistent with optimal compared experimental references data. At the same circumstance, the computed bond lengths ascribed to N2-C6, N2-C6, N2-C7 and N2-C6 for compounds 13, 15, 18 and 23 respectively, were found as 1.390, 1.399, 1.393 and 1.397 correspondingly, in good agreement with corresponding experimental references data. Additionally, the selected bond angles connectivity presented in Tables 1, 2, 3, and 4 exhibited minor slightly deviations than the optimal bond angles recorded experimentally. Furthermore, the aromatic rings planarity connected to the core ring (pyrazoline ring) can be illustrated via computed dihedral angles values. From the calculated dihedral angles presented in tables (1S–4S), we found that the pyrazoline ring for compounds 13, 15, 18 and 23 respectively, didn’t planar. Also, an aromatic ring connected to the N2 nitrogen atom in the core ring is co-planar. In a contrary, both aromatic rings that are connected to C1 and C4 in the core ring respectively, are perpendicular to the same plane of given compounds. All small discrepancy that has been found for bond angles and dihedral angles computed for given compounds may be attributed to that the theoretical computations performed in the gas phase, but in the experimental ones conducted on the solid phase of a molecule.

Vibrational Spectra Analysis

The experimental and computational IR spectra for compounds 13, 15,18 and 23 are given in Figs. 5, 6, 7, and 8.

Fig. 5
figure 5

a Experimental and (b) Simulated IR spectra of compound 13 at DFT (B3LYP) with 6–31 G(d, p) basis set in gas phase

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Fig. 6
figure 6

a Experimental and (b) Simulated IR spectra of compound 15 at DFT (B3LYP) with 6–31 G(d, p) basis set in gas phase

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Fig. 7
figure 7

a Experimental and (b) Simulated IR spectra of compound 18 at DFT (B3LYP) with 6–31 G(d, p) basis set in gas phase

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Fig. 8
figure 8

a Experimental and b Simulated IR spectra of compound 23 at DFT (B3LYP) with 6–31 G(d, p) basis set in gas phase

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The characteristic computed (unscaled and scaled) and experimental vibrational frequency values for compounds studied are presented in Tables 5, 6, 7, and 8.

Table 5 Experimental and calculated vibrational frequencies of compound 13
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Table 6 Experimental and calculated vibrational frequencies of compound 15
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Table 7 Experimental and calculated vibrational frequencies of compound 18
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Table 8 Experimental and calculated vibrational frequencies of compound 23
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As seen from figs and tables, the C-H stretching bands of aromatic rings for compounds computed are found in the range 3111–2926 cm−1 and experimentally are observed at 3069–3032 cm−1 in the functional group region of the spectrum in excellent agreement with simulated IR spectra. In the finger print region of the spectrum, both the C=C and the C=N stretching bands of aromatic rings for compounds computed are appeared in the range of 1545–1608 cm−1 as compared with experimental that observed at 1493–1597 cm−1 in good accordance for the simulated ones. The simulated deformations modes of the CH2 and C-H for compounds are exhibited at 1436–1502 cm−1 respectively and are observed experimentally at 1416–1502 cm−1 in close corresponding agreement for vibrational frequencies. The C-F stretching bands of aromatic rings for compounds computed are found in the range 1234–1233 cm−1 and experimentally are observed at 1219–1232 cm−1 with great accordance for calculated frequencies. Furthermore, the rocking (ρ CH3) for compounds 15 and 23 are characterized at 968–1023 cm−1 and are observed experimentally at 1000–980 cm−1 respectively that are also agreed with computed frequency values. In addition to that, the C-Cl stretching bands of aromatic rings for compounds 13 and 18 are found at 527–540 cm−1 and are observed experimentally at 559–525 cm−1 respectively with a great agreement for their computed frequency values.

UV-Vis Absorption and Fluorescence Emission Spectra Analysis

Time-dependent density function theory (TD-DFT) calculations were applied for computing the absorption and emission spectra at TD-DFT/B3LYP/6–31 G(d,p) level of theory for compounds 13,15,18 and 23.

The calculated absorption maxima (λmax), excitation energies, oscillator strengths (ƒ), and the calculated emission maxima(λmax) with a comparison of experimental data are given in Table 9.

Table 9 The experimental, computed UV-Vis absorption and fluorescence emission spectra for compounds 13, 15, 18 and 23
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The corresponding experimental, simulated UV-vis absorption and emission spectra are depicted in Fig. 9.

Fig. 9
figure 9

The experimental UV-Vis absorption and fluorescence emission spectra for compounds 13, 15, 18 and 23

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As seen from Fig. 9, selected compounds (13,15,18 and 23) experimentally exhibited two characteristic maximum absorption wavelengths (λmax) within 240 and 380 nm that were attributed to a π-π* and n-π* transitions, respectively. With comparison with the theoretical data presented in Fig. 10, we found a good agreement with absorption maxima for π-π* transitions with higher increasing for n-π* than the experimental ones. On the other hand, the theoretical emission maxima for four compounds (13,15,18 and 23) were found recorded much higher values shifts than the experimental ones as presented in Table 9 and Figs. 9 and 10, this may be attributed to the calculation of emission maxima in a vacuum in contrary for experimental ones that were measured in chloroform.

Fig. 10
figure 10

The simulated UV-Vis absorption and fluorescence emission spectra for compounds 13, 15, 18 and 23 computed at the DT-DFT/B3LYP/6-31G(d,p) level of theory in vacuum

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Frontier Molecular Orbital Analysis

The two-pivotal molecular orbitals, one is highest occupied molecular orbital (HOMO) illustrates remotest molecular orbital filled by electron and acts as an electron donor. The other one is lowest unoccupied molecular orbital (LUMO) depicts inmost molecular orbital unfilled by electron and acts as an electron acceptor. These molecular orbitals are called the frontier molecular orbitals (FMOs). Between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) creates energy gaps. This energy gap value provides a powerful tool to determine electronic transition, optical properties, kinetic stability and chemical reactivity of a molecule.

The dipole moment, optimized energy level, HOMO and LUMO energy values and energy gap values for compounds, 13, 15, 18 and 23 were computed via Gaussian 09 W program package at DFT/B3LYP method and 6-31G(d,p) basis set in the gas phase. The calculated data are given in Table 10.

Table 10 The dipole moment, optimized energy level, HOMO LUMO energy values and energy gap values for compounds, 13, 15, 18 and 23
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As presented in Table 10, we found that the dipole moment of compound 18 is greater than all compounds and indicates that it is more polar compound than the others. Also, energy gap value for compound 23 indicates that it is more reactive slightly than the others. In addition to that, all energy gap values ensure that all synthesized compounds are stable and polar compounds.

The 3D plots of frontier molecular orbitals of compounds 13,15,18 and 23 in gas phase are depicted in Fig. 11. As seen from Fig. 11 the HOMOs density of electrons for compounds, 13, 15, 18 and 23 are concentrated at the nitrogen atom of pyrazoline moiety with distribution over two rings at positions 1, and 3 at 2-pyrazoline moiety. The electronic transition of HOMO to LUMO was exhibited as charge transfer from the aromatic ring located at the position number one with respect to pyrazoline moiety with effective participation for the second aromatic ring in position number 3 at central pyrazoline moiety. On the other hand, the third aromatic ring attached at position five at central pyrazoline moiety appeared had no any participation in all electronic transition due to its spatial position out of the plane and it was remoted than central pyrazoline moiety. In overall these electronic transitions were attributed to a π to π* transition.

Fig. 11
figure 11

The 3D plots of frontier molecular orbitals for compounds 13,15,18 and 23 in gas phase with their energy levels computed at the DFT/B3LYP/6-31G (d,p) level of theory

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Molecular Electrostatic Potential (MEP)

The molecular electrostatic potential (MEP) is a 3D plot implied charge distribution onto surfaces of molecules. It gives a profound prediction, interpretation for reactivity of both electrophilic and nucleophilic attack and hydrogen bonds interactions.

The molecular electrostatic potential for compounds 13,15,18 and 23 was computed via using the optimized molecular structures at the DFT/B3LYP method and 6-31G (d, p) basis set in the gas phase and visualized by Gaussian View 6.0 program package.

The 3D plots of the MEP for compounds 13,15,18 and 23 are given in Fig. 12.

Fig. 12
figure 12

The 3D plots of MEP surfaces for (a) compound 13, (b) compound 15, (c) compound 18, and (d) compound 23 computed at the DFT/B3LYP/6-31G(d,p) level of theory (a.u.)

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As depicted in Fig. 12, the electrostatic potentials onto surfaces of compounds 13, 15,18 and 23 are exhibited with various colors. The color code map is in the range between (intense red) negative region to (intense blue) positive region. The electrostatic potentials decrease in the order blue> green> yellow>orange>red. Therefore, we can see from MEP map for compounds 13, 15, 18 and 23 the negative regions are basically localized onto both nitrogen atom labeled by (N3) presented at pyrazoline moiety and distributed over first aromatic ring attached by nitrogen atom labeled by (N2) at pyrazoline moiety with slightly distribution of negative electrostatic potentials onto the second aromatic ring attached by carbon atom labeled by (C4) at pyrazoline ring.

On the other hand, the positive regions hovered onto the third aromatic ring attached by carbon atom labeled by (C1) at pyrazoline ring for compounds 13,15,18 and 23. Addition to that the zero potential regions also were appeared in green color for all compounds studies.

NMR Spectra Analysis

The optimized molecular structures of the active novel pyrazoline compounds 13, 15,18, and 23 are used to compute the NMR spectra using the DFT at B3LYP method via 6–311 + G(2d,p) basis set in the gas phase through the GIAO method. The theoretical 1H and 13C NMR chemical shifts values for compounds 13, 15,18 and 23 were computed at the same level of the theory in ppm relative to TMS. The calculated 1H and 13C NMR chemical shifts values for compounds 13, 15,18 and 23 are given in Tables 11, 12, 13, and 14.

Table 11 The experimental and computed 1H and 13C NMR isotropic chemical shifts values in ppm (with respect to TMS) for compound 13
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Table 12 The experimental and computed 1H and 13C NMR isotropic chemical shifts values in ppm (with respect to TMS) for compound 15
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Table 13 The experimental and computed 1H and 13C NMR isotropic chemical shifts values in ppm (with respect to TMS) for compound 18
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Table 14 The experimental and computed 1H and 13C NMR isotropic chemical shifts values in ppm (with respect to TMS) for compound 23
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As appeared in Table 11, for compound 13, the experimental and calculated carbon-13 chemical shifts values for C5 and C1 atoms were found to be 43.4/46.6 ppm (exp./cal.) and 64.0/68.55 ppm (exp./cal.) respectively which are attributed to the presence of pyrazolinyl carbon atoms. Furthermore, the experimental and calculated carbon-13 chemical shifts values for aromatic rings have been exhibited at the interval 113.5–163.4/113.91–171.47 ppm (exp./cal.). On the other hand, the experimental and calculated 1H NMR chemical shifts values for H28, H27, and H26 atoms appeared at 3.08/2.88 ppm (exp./cal.), 3.81/3.78 ppm and 5.28/5.21 ppm (exp./cal.) respectively which are attributed to the upfield of the methylene protons, downfield of methylene protons and methine proton respectively. In the same circumstance, the experimental and calculated 1H NMR chemical shifts values for aromatic rings have been exhibited at the interval 6.78–7.65/6.35–8.62 ppm (exp./cal.).

Similarly, in Table 12 for compound 15, the experimental and calculated carbon-13 chemical shifts values for C29, C5 and C1 atoms were found to be 21.42/22.49 ppm (exp./cal.), 43.7/47.52 ppm (exp./cal.) and 63.8/69.13 ppm (exp./cal.) respectively which are attributed to presence of 4-methylphenyl, pyrazolinyl carbon atoms respectively. Furthermore, the experimental and calculated carbon-13 chemical shifts values for aromatic rings have been exhibited at the interval 113.4–163.4/114.59–172.39 ppm (exp./cal.). On the other hand, the experimental and calculated 1H NMR chemical shifts values for H42, H43, H44, H28, H27, and H26 atoms appeared at 2.04/2.01 ppm (exp./cal.), 2.39/2.56 ppm (exp./cal.), 2.39/2.56 ppm (exp./cal.), 3.10/2.96 ppm (exp./cal.), 3.82/3.87 ppm (exp./cal.) and 5.24/5.23 ppm (exp./cal.) respectively which are attributed to 4-methylphenyl, upfield of the methylene protons, downfield of methylene protons and methine proton respectively. In the same circumstance, the experimental and calculated 1H NMR chemical shifts values for aromatic rings have been exhibited at the interval 6.79–7.64/6.42–8.72 ppm (exp./cal.).

As given in Table 13 for compound 18, the experimental and calculated carbon-13 chemical shifts values for C5 and C1 atoms were found to be at 43.6/51.15 ppm (exp./cal.) and 63.9/68.17 ppm (exp./cal.) respectively which are attributed to presence of pyrazolinyl carbon atoms. Furthermore, the experimental and calculated carbon-13 chemical shifts values for aromatic rings have been exhibited at the interval 114.6–163.5/115.09–172.56 ppm (exp./cal.). On the other hand, the experimental and calculated 1H NMR chemical shifts values for H31, H32 and H30 atoms were appeared at 3.25/3.64 ppm (exp./cal.), 3.93/3.80 ppm (exp./cal.) and 5.26/5.46 ppm (exp./cal.) respectively which are attributed to the upfield of the methylene protons, downfield of methylene protons and methine proton respectively. In the same circumstance the experimental and calculated 1H NMR chemical shifts values for aromatic rings have been exhibited at the interval 7.50–8.17/6.35–8.15 ppm (exp./cal.). lastly, as presented in Table 14 for compound 23, the experimental and calculated carbon-13 chemical shifts values for C25, C5 and C1 atoms were found to be 20.5/19.78 ppm (exp./cal.), 43.5/52.56 ppm (exp./cal.) and 64.2/73.59 ppm (exp./cal.) respectively which are attributed to presence of 4-methylphenyl, pyrazolinyl carbon atoms respectively. Furthermore, the experimental and calculated carbon-13 chemical shifts values for aromatic rings have been exhibited at the interval 113.6–163.4/119.86–172.68 ppm (exp./cal.). On the other hand, the experimental and calculated 1H NMR chemical shifts values for H50, H49, H48, H31and H30 atoms appeared at 2.28/1.85 ppm (exp./cal.), 2.28/1.35 ppm (exp./cal.), 2.28/1.45 ppm (exp./cal.), 3.25/3.47 ppm (exp./cal.), and 5.27–5.32/4.94 ppm (exp./cal.) respectively which are attributed to 4-methylphenyl, upfield of the methylene protons, downfield of methylene protons and methine proton respectively. In the same circumstance, the experimental and calculated 1H NMR chemical shifts values for aromatic rings have been exhibited at the interval 7.01–8.19/6.15–13.98 ppm (exp./cal.).

In general, all the theoretical 1H and 13C NMR chemical shifts values for compounds 13, 15,18 and 23 have been observed in accordance with experimental data that were seen in Tables 11, 12, 13 and 14 with slight deviation in some values experimentally due to the computational simulation of calculations were performed in the gas phase. The corresponding figures for experimental and theoretical charts of 1H and 13C NMR chemical shifts values for compounds 13, 15,18 and 23 were given in Figs. (1S–8S).

Conclusion

In the present work, four active new synthesized compounds were selected from twenty-one analogues due to their high fluorescence quantum yield values than the reference value (quinine sulfate) and were characterized chemically and spectrally. Density functional theory (DFT) computations, FT-IR, UV-visible, emission spectra and NMR spectra for the optimized molecular structures were successfully performed in good agreement with experimental data. Via the HOMO-LUMO analysis and MEP maps, we could track and determine electron density onto the surfaces, chemical stability, reactivity and dipole moment for selected compounds. The computational studies could be a powerful tool that could assist experimental data for illustration and prediction optical properties for given compounds in an excellent visualization.