Abida Ashrafae,
Muhammad Khalid*b,
Muhammad Nawaz Tahirc,
Muhammad Yaquba,
Muhammad Moazzam Naseer
d,
Ghulam Mustafa Kamalb,
Bullo Saifullah
bg,
Ataualpa Albert Carmo Braga
f,
Zahid Shafiq*a and
Waqar Rauf
h
aInstitute of Chemical Sciences, Bahauddin Zakariya University, Multan 60800, Pakistan. E-mail: zahidshafiq25@hotmail.com
bDepartment of Chemistry, Khwaja Fareed University of Engineering & Information Technology, Rahim Yar Khan-64200, Pakistan. E-mail: muhammad.khalid@kfueit.edu.pk; Khalid@iq.usp.br
cDepartment of Physics, University of Sargodha, Sargodha, Pakistan
dDepartment of Chemistry Quaid-i-Azam University Islamabad, 45320, Pakistan
eDepartment of Chemistry, Kutchery Campus, The Women University Multan, Multan 60000, Pakistan
fDepartamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Avenida Professor Lineu Prestes, 748, São Paulo 05508-000, Brazil
gDepartment of Biomedical Engineering, Mehran University of Engineering Technology, Jamshoro, Sindh 76062, Pakistan
hNational Institute of Biotechnology and Genetic Engineering (NIBGE), P. O. Box 577, Faisalabad, Pakistan
First published on 28th October 2019
In this work, we report the efficient synthesis of novel (hydroxybenzoyl)pyrido[2,3-d]pyrimidine heterocycle derivatives: 6-(2-hydroxy-5-methylbenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (6a), 6-(5-fluoro-2-hydroxybenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (6b), 6-(5-ethyl-2-hydroxybenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (6c) and 6-(2-hydroxy-5-isopropylbenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (6d). The chemical structures of the title compounds were ascertained by spectral techniques including 1H, 13C NMR, UV-visible and FT-IR spectroscopy as well as single-crystal X-ray diffraction analysis. Additionally, density functional theory (DFT) and time-dependent (TD-DFT) computation were adopted to analyze the electronic structures of 6a–d. Compounds 6a–d were computed in the ground state for FT-IR spectroscopic and natural bond orbital (NBO) analysis by DFT/B3LYP with the 6-311+G(d,p) basis set. UV-vis spectroscopic and HOMO and LUMO energy values for 6a–d were determined via TD-DFT/B3LYP with the 6-311+G(d,p) basis set. The optimized geometric parameters, UV-vis findings, and vibrational frequencies indicate good consistency with the experimental data. NBO analysis was conducted to explore the interactions and charge transfer among different orbitals in the title compounds. The HOMO and LUMO band gap (ΔE) values for 6a–d were found to be 3.93, 3.91, 4.10 and 3.91 eV, respectively. Molecular electrostatic potential (MEP) analysis explored the reactivity of the title compounds by predicting their nucleophilic as well as electrophilic sites.
Owing to their biological prominence, substantial effort has been focused towards synthetic strategies for pharmacologically active pyrido[2,3-d] pyrimidines, though there remain many challenges for the synthesis of naturally occurring complex molecules.2
In continuation of our research work,16–20 we have synthesized some bioactive nitrogen- and oxygen-containing (hydroxybenzoyl)pyrido[2,3-d]pyrimidine heterocycles. Quantum chemical approaches provided promising insights regarding the chemical and biological systems that often found good agreement with the experimental results. Nowadays, the term “quantum chemical approaches” is used almost synonymously with density functional theory (DFT). DFT calculations provide a reasonable compromise between cost and accuracy. Many scientific publications have revealed that the DFT findings have been in line with experiments.21 Moreover, DFT-based findings have been recognized as being better than the findings obtained from ab initio methods.22 This might be one of the reasons behind the acceptance of DFT and it is extensively used in different fields of chemistry. Many DFT-based studies have addressed the various structural and mechanistic aspects of chemical systems.23 In this context, we performed DFT calculations for the molecular geometry to understand the structural parameters, vibrational spectroscopy, NBO analysis for intermolecular interactions and MEP for chemical reactivity surfaces, HOMO–LUMO and nonlinear optics (NLO) analysis for the electronic properties of (hydroxybenzoyl)pyrido[2,3-d]pyrimidine heterocycle derivatives.
Crystal data | 6a | 6b | 6c | 6d |
---|---|---|---|---|
CCDC | 1909617 | 1909620 | 1909619 | 1909618 |
Chemical formula | C16H13N3O4 | C15H10FN3O4 | C17H15N3O4 | C18H17N3O4 |
Mr | 311.29 | 315.26 | 325.32 | 339.34 |
Crystal system, space group | Monoclinic, P21/n | Monoclinic, C2/c | Monoclinic, P21/c | Triclinic, P![]() |
Temperature (K) | 296 | 296 | 296 | 296 |
a, b, c (Å) | 8.1712 (11), 13.873 (2), 12.3934 (17) | 23.336 (3), 6.9240 (6), 17.2853 (18) | 11.7250 (5), 13.3565 (6), 10.1992 (4) | 8.4030 (4), 9.6898 (4), 10.9110 (7) |
α, β, γ (°) | 92.098 (6) | 108.798 (3) | 114.332 (2) | 105.870 (2), 98.586 (2), 102.351 (4) |
V (Å3) | 1403.9 (3) | 2643.9 (5) | 1455.37 (11) | 814.10 (7) |
Z | 4 | 8 | 4 | 2 |
Radiation type | Mo Kα | Mo Kα | Mo Kα | Mo Kα |
μ (mm−1) | 0.11 | 0.13 | 0.11 | 0.10 |
Crystal size (mm) | 0.44 × 0.30 × 0.28 | 0.44 × 0.38 × 0.30 | 0.44 × 0.38 × 0.36 | 0.41 × 0.30 × 0.27 |
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||||
Data collection | ||||
Tmin, Tmax | 0.940, 0.980 | 0.930, 0.970 | 0.930, 0.975 | 0.940, 0.985 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 9802, 3315, 2477 | 8315, 3120, 2521 | 8838, 3413, 2687 | 8321, 3154, 2336 |
Rint | 0.057 | 0.031 | 0.035 | 0.032 |
(sin![]() |
0.659 | 0.658 | 0.659 | 0.617 |
![]() |
||||
Refinement | ||||
R[F2 > 2σ(F2)], wR(F2), S | 0.055, 0.172, 1.04 | 0.043, 0.123, 1.04 | 0.046, 0.133, 1.05 | 0.048, 0.156, 1.04 |
Δ〉max, Δ〉min (e Å−3) | 0.38, −0.28 | 0.26, −0.19 | 0.29, −0.20 | 0.23, −0.23 |
The information regarding the type of diffractometer, absorption correction and H-atom treatment can be seen in Table S17.† The molecular structures of 6-(2-hydroxybenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4-diones 6a–d along with the crystallographic numbering schemes are shown in Fig. 2. As shown in Fig. 2, the benzoyl moiety present at the 6-position of 1-methylpyrido[2,3-d]pyrimidine-2,4-dione is tilted from the methylpyrido[2,3-d]pyrimidine-2,4-dione plane in 6a–d with dihedral angles of C(6)–C(8)–C(9)–C(13) = 49.40(2)° in 6a, C(6)–C(9)–C(10)–C(11) = 30.1(2)° in 6c, C(1)–C(10)–C(11)–C(15) = −150.19(16)° in 6d and C(6)–C(7)–C(8)–C(12) = 146.45(14)° in 6b. In all four compounds, the sigma bond on one side of the central carbonyl that is acting as a bridge between the phenyl and the 1-methylpyrido[2,3-d]pyrimidine-2,4-dione rings has frozen rotation owing to the presence of strong intramolecular hydrogen bonds [O(1)–H(1)⋯O(2), 1.79(3) Å in 6a; O(1)–H(1)⋯O(2), 1.89 Å in 6c; O(1)–H(1)⋯O(2), 1.89 Å in 6d; and [O(1)–H(1)⋯O(2), 1.83 Å in 6b], whereas the sigma bond on the other side can freely rotate. Owing to this rotation, the substituents present on the hydroxybenzoyl can adopt two arrangements, i.e. cis or trans to the methyl group present on the pyrido[2,3-d]pyrimidine-2,4-dione. In both 6a and 6c where the substituents are methyl and ethyl, respectively, on the hydroxybenzoyl moiety, this arrangement is cis while it is trans in 6d and 6b where the substituents are isopropyl and fluorine, respectively, on the hydroxybenzoyl moiety.
![]() | ||
Fig. 2 The molecular structures (ORTEP diagram) of 6-(2-hydroxybenzoyl)-1-methylpyridopyrimidine-2,4-diones 6a–d. Displacement ellipsoids are drawn at the 50% probability level. |
An interesting feature of compounds 6a–d is their molecular packing in the solid state owing to the presence of various hydrogen bond donor and acceptor sites (Fig. 2 and 3). Interestingly, in compound 6a the amide moiety in pyrido[2,3-d]pyrimidinedione interacts with the hydroxybenzyl moiety through hydrogen bonding [N(2)–H(2A)⋯O(2), 2.00 Å; O(1)–H(1)⋯O(3), 2.42(2) Å] providing a ten-membered ring rather than forming the centrosymmetric R22(8) {⋯H–N–CO}2 synthon, resulting in 1D zig-zag supramolecular chains. However, this centrosymmetric R22(8) {⋯H–N–C
O}2 synthon is observed in both 6c [N(2)–H(2A)⋯O(3), 2.02 Å] and 6b [N(3)–H(3A)⋯O(4), 1.98 Å]. Interestingly, none of the arrangement observed in 6a, 6c and 6b is present in the solid-state structure of 6d, most probably owing to the presence of a bulky isopropyl group. The packing of compound 6d is mainly driven by N–H⋯O [N(2)–H(2)⋯O(1), 2.16 Å] and C–H⋯O [C(6)–H(6)⋯O(4), 2.496 Å] hydrogen bonds (Fig. 4).
![]() | ||
Fig. 4 3D packing of (a) 6a along the c-axis; (b) 6c along the b-axis; (c) 6d along the a-axis; and (d) 6b along the b-axis in the solid state. |
For 6b, the experimentally determined values of the C–N bond lengths for N1–C11, N1–C12, N2–C11, N2–C14 and N3–C15 were 1.336(18), 1.324(19), 1.384(17), 1.367(19), and 1.378(18) Å, respectively. However, the DFT values of the C–N bond lengths were found to be 1.339, 1.327, 1.386, 1.396 and 1.390 Å, respectively (Table S2†). Further, the experimentally determined values for the O1–C1, O2–C7, O3–C14 and O4–C14 bond lengths were 1.351(18), 1.242(16), 1.212(17) and 1.222(17) Å, respectively, whereas the DFT values of these C–O bond lengths were found to be 1.340, 1.239, 1.215 and 1.212 Å, respectively (Table S2†). The experimentally determined bond angles values for F1–C4–C3, O2–C7–C6, O3–C15–N3, N1–C11–N2, C13–N2–C14 and N3–C15–C10 were 118.2(13), 120.8(12), 121.2(12), 116.7(11), 117.8(12) and 113.9(11)°, while the DFT values for the same angles are 118.8, 120.7, 121.8, 116.8, 118.2 and 113.0°, respectively (Table S2†).
For 6c, the experimentally determined values for the N1–C11, N1–C12, N2–C15, N2–C16, N3–C12, N3–C16 and N3–C17 bond lengths were 1.332(19), 1.336(17), 1.391(19), 1.393(19), 1.387(18), 1.395(18) and 1.470(18) Å, respectively. The DFT values of the above-mentioned bond lengths were found to be 1.333, 1.337, 1.371, 1.380, 1.383, 1.380 and 1.468 Å, respectively. The experimentally determined values for the O1–C1, O2–C9, O3–C15 and O4–C16 bond lengths were 1.340(2), 1.239(18), 1.214(17) and 1.213(18) Å, respectively. The DFT-based values of the above-mentioned bond lengths (C–O) were 1.349, 1.228, 1.220 and 1.210 Å, respectively (Table S3†). The experimentally determined bond angles observed for O1–C1–C2, O2–C9–C6, O3–C15–C13, O4–C16–N3, N1–C11–C10, N2–C16–N3 and C3–C4–C5 were 117.8(14), 121.1(13), 125.4(13), 123.6(14), 124.3(12), 115.2(13) and 117.5(14)° while their DFT values were found to be 117.9, 120.8, 124.1, 122.8, 124.7, 116.2 and 117.1°, respectively (Table S3†).
Furthermore, for 6d, the experimentally determined values of the N1–C14, N1–C15, N2–C16, N2–C17, N3–C14, N3–C17 and N3–C18 bond lengths were 1.332(2), 1.323(2), 1.368(2), 1.376(2), 1.384 (2), 1.377(2) and 1.462(2) Å, respectively and the DFT values were 1.339, 1.328, 1.390, 1.394, 1.387, 1.395 and 1.471 Å, respectively (Table S4†). The experimentally obtained C–O bond lengths for O1–C2, O2–C10, O3–C16 and O4–C17 were 1.352(2), 1.232(2), 1.210(2) and 1.205(2) Å, respectively, while the DFT values were observed to be 1.341, 1.240, 1.215 and 1.213 Å, respectively (Table S4†). The experimentally determined bond angles for O1–C2–C3, O2–C10–C1, O3–C16–N2, N1–C14–N3, N1–C14–C13 and C2–C3–C4 were 118.3(16), 121.6(16), 121.5(17), 116.7(15), 123.2(16) and 120.7(18)° while the DFT values were 117.8, 121.2, 121.1, 116.8, 122.5 and 120.5°, respectively. The comparative analysis reveals that the experimentally determined bond lengths and bond angles are slightly lower than the calculated parameters, as can be seen in Tables S1–S4.† The observed difference between the DFT and experimental findings might be because of the medium effect. Overall, the obtained structural results for 6a–d from the DFT and XRD studies show good agreement, as can be seen in Tables S1–S4,† respectively.
![]() | (1) |
The value of the perturbation stabilization energy [E(2)] depicts the level of conjugation in the whole system. The data for the NBO study regarding molecules 6a–d was obtained using the B3LYP/6-311+G(d,P) level of theory, as tabulated in Tables S9–S12.† The highest transitions (π → π*) take place as π(N6–C28) → π*(C24–C29) with 43.15 kcal mol−1, π(C11–C19) → π*(C12–C14) with kcal mol−1, π(C6–C30) → π*(C27–C28) with kcal mol−1 and π(C10–C11) → π*(C12–C14) with 170.92 kcal mol−1 for 6a–d, respectively. These are the largest values among the stabilization energies given in Tables S9–S12.† The stabilization energy value of 6b is higher than those for the other compounds 6a, 6c and 6d owing to the stronger intramolecular hyper conjugative interactions, which might be due to the fluoro group. Transitions σ(O1–H2) → σ*(C10–C12), σ(O5–C33) → σ*(C24–C33), σ(C36–H39) → σ*(C36–H39) and σ(C39–H42) → σ*(C39–H42) shown stabilization energy values of 6.07, 65.09, 53.30 and 51.83 kcal mol−1 for 6a–d, respectively. These are the highest σ → σ* stabilization energies in the studied compounds, which result in a strong interaction between the donor (σ) and the acceptor (σ*). In the case of the resonance, the transitions LP(N9) → σ*(O5–C32), LP(N9) → π*(C35–C37), LP(N9) → σ*(C35–C37) and LP(N7) → π*(O4–C37) exhibit stabilization energy values of 70.30, 51.05, 78.19 and 52.43 kcal mol−1 for 6a–d, respectively, as the largest energy values (see Tables S9–S12†). The lowest values of 5.53, 5.88, 5.45 and 7.05 kcal mol−1 were exhibited by LP(N6) → σ*(N9–C28), LP(F1) → σ*(C16–C17), LP(N6) → σ*(N9–C30) and LP(N9) → σ*(C39–C40) in 6a–d, respectively (see Tables S9–S12†). Subsequently, on the basis of the NBO analysis, it can be concluded that the increased stability in these systems (6a–d) is mainly contributed by strong intramolecular hyper conjugative interactions.
For 6b, the electron distribution of the HOMOs is also mainly dispersed over methyl benzoyl moiety, while the LUMO electron distribution is mainly localized over the whole compound with the exception of the methyl group and the C–N bond of the pyridopyrimidine-2,4-dione moiety as well as only a bit extended on the carbonyl functional group of the pyridopyrimidine-2,4-dione moiety (see Fig. 6).
For 6c, the electron distribution of the HOMOs is mainly dispersed over the pyridopyrimidine-2,4-dione moiety, while the LUMO electron distribution is are mainly localized on over the pyridopyrimidine-2,4-dione moiety as well as only a bit extended on the carbonyl functional group of the benzoyl moiety (see Fig. 7).
Further, for 6d, the electron distribution of the HOMOs is mainly dispersed over the methyl benzoyl moiety, while the LUMO electron distribution is mainly localized over the compound with the exception of the methyl group of the benzoyl moiety (see Fig. 8).
Subsequently, this mechanism reveals the existence of ICT character from HOMO to LUMO orbitals.
In addition, the calculated energy values for the HOMO–LUMO and energy gap (Egap) for these compounds are tabulated in Table 2. Subsequently, the energy band gaps (Egap) of the HOMO–LUMO levels for compounds 6a–d are 3.93 eV, 3.91 eV, 4.1 eV and 3.91 eV, respectively.
6a | 6b | 6c | 6d | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
MO | Energy | ΔE | MO | Energy | ΔE | MO | Energy | ΔE | MO | Energy | ΔE |
a E = energy; ΔE (eV) = ELUMO − EHOMO; HOMO, highest occupied molecular orbital; LUMO, lowest unoccupied molecular orbital; MO, molecular orbital. | |||||||||||
HOMO | −6.6 | 3.93 | HOMO | −6.8 | 3.91 | HOMO | −10.6 | 4.10 | HOMO | −6.5 | 3.91 |
LUMO | −2.6 | LUMO | −2.9 | LUMO | −6.5 | LUMO | −2.6 | ||||
HOMO−1 | −7.2 | 4.8 | HOMO−1 | −7.3 | 4.7 | HOMO−1 | −10.7 | 5.10 | HOMO−1 | −7.2 | 4.78 |
LUMO+1 | −2.4 | LUMO+1 | −2.5 | LUMO+1 | −5.6 | LUMO+1 | −2.4 | ||||
HOMO−2 | −7.7 | 6.23 | HOMO−2 | −7.9 | 6.24 | HOMO−2 | −11.2 | 6.10 | HOMO−2 | −7.6 | 6.291 |
LUMO+2 | −1.5 | LUMO+2 | −1.7 | LUMO+2 | −5.2 | LUMO+2 | −1.4 |
The energy gaps of the studied compounds decrease in the following order:
6c > 6a > 6b = 6d |
The computing calculations show that the electronic properties of the four derivatives might be affected through by the electron donating capability of the substituents, which might effectively tune their optical characteristics and the lower Egap explains that the aforesaid derivatives would contain strong electron transfer ability and larger second-order NLO properties.42,43
Moreover, the calculated energy values for the FMOs are used for calculating the values of the global reactivity descriptors.44–47
The electronic affinity (A) and ionization potential (I) have been calculated in a vertical manner using eqn (2) and (3).
I = EcN−1 − EoN | (2) |
A = EoN − EAN+1 | (3) |
Hardness and electronegativity values have been calculated using eqn (4) and (5).
![]() | (4) |
![]() | (5) |
Electrophilicity calculations were performed to establish the charge transfer process. This describes the relationship between energy variation and the maximum electrons transferred.
![]() | (6) |
The ability of a chemical species to donate or accept an electron can be explained with the help of two descriptors. eqn (7) and (8) were used to calculate the donating and accepting ability of 6a–d, respectively.
![]() | (7) |
![]() | (8) |
Eqn (9) was used to calculate the softness value.
![]() | (9) |
The results obtained from eqn (2)–(9) are summarized in Table 3.
Com | I | A | X | η | μ | ω | ω− | ω+ | σ |
---|---|---|---|---|---|---|---|---|---|
6a | 4.80 | 4.43 | 4.62 | 0.18 | −4.62 | 57.42 | 59.75 | 55.13 | 2.69 |
6b | 5.46 | 4.63 | 5.04 | 0.41 | −5.04 | 30.79 | 33.36 | 28.32 | 1.21 |
6c | 5.20 | 4.43 | 4.81 | 0.38 | −4.81 | 30.09 | 32.55 | 27.73 | 1.30 |
6d | 5.14 | 4.43 | 4.78 | 0.35 | −4.78 | 32.16 | 34.59 | 29.81 | 1.41 |
The highest ionization potential was calculated to be 5.46 eV for 6b, while the lowest ionization potential was observed for 6a with a value of 5.19 eV. The ionization potential decreases in the following order: 6b > 6c > 6d > 6a. The highest electron affinity value was found to be 4.63 eV for 6b, while the other three derivatives have the same electron affinity of 1.43 eV. The ionization potential and electron affinity can be used to describe the electron releasing and accepting capabilities of the investigated molecules, which are directly related to the energy of the HOMOs and LUMOs. Overall, the ionization potential values are observed to be larger than the electron affinity values, highlighting the better electron donating capability of the investigated molecules (6a–d). Usually, a molecule with a high energy gap can be considered as a hard, non-reactive, stable species, and vice versa. The global hardness values of our studied systems were found to descend in the following order; 6b > 6c > 6d > 6a (Table 3). A similar trend is observed for the electronegativity values of the studied compounds (6a–d) (Table 3). The chemical potential value of any system can be used to describe its reactivity and stability. Molecules with greater chemical potential values could be considered as less reactive and more stable, and vice versa. In decreasing order, the chemical potential values for the studied compounds are: [6b (μ = −5.04 eV)] > [6c (μ = −4.81 eV)] > [6d (μ = −4.78 eV)] > [6a (μ = −4.62 eV)].
The global softness values were found to be 2.69, 1.21, 1.30 and 1.41 eV for 6a–d, respectively. These values have a greater magnitude as compared to their global hardness values. The global electrophilicity (ω) decreases in the following order: 6a (57.42 eV) > 6d (32.16 eV) > 6b (30.79 eV) > 6c (30.09 eV). In decreasing order, the electron donor capability (ω−) values are: 6a (59.75 eV) > 6d (34.59 eV) > 6b (33.36 eV) > 6c (32.55 eV) and the electron acceptor capability (ω+) values are: 6a (55.13 eV) > 6d (29.81 eV) > 6b (28.32 eV) > 6c (27.73 eV).
Overall, the electron donating capability (ω−) values were found to be higher than the electron accepting (ω+) capability values. The ionization energy and electron affinity values represent the ability of an atom to donate and accept electrons, respectively. In our compounds, the ionization energies were much higher than the electron affinity values, which supports the finding that the electron donating ability (ω−) of the investigated compounds is higher than their electron accepting ability (ω+). The aforementioned results show that all investigated molecules have good kinetic stability and electron donating capability.
Com | Exp λ (nm) | DFT λ (nm) | E (cm−1) | f | MO contributions |
---|---|---|---|---|---|
a Com = compounds; Exp = experimental; E = Excitation energy; λ = wavelength; f = oscillator strength; MO = molecular orbitals; H = HOMO; L = LUMO; λ (nm).b Acetone.c DMSO.d 1,4-Dioxane. | |||||
6a | 364 | 27![]() |
0.1408 | H → L (97%) | |
332b | 342 | 29![]() |
0.0017 | H → L+1 (99%) | |
327 | 30![]() |
0.0131 | H-4 → L (27%), H-3 → L (29%), H-2 → L (15%), H-1 → L (23%) | ||
305c | 302 | 33![]() |
0.2089 | H-1 → L (52%), H-1 → L+1 (27%), H-4 → L (4%), H-3 → L (3%), H-3 → L+1 (3%), H-2 → L (6%) | |
300d | 294 | 34![]() |
0.0761 | H-4 → L+1 (10%), H-3 → L+1 (33%), H-1 → L (13%), H-1 → L+1 (24%), H-3 → LUMO (4%), H-2 → L (9%), H-2 → L+1 (2%) | |
292 | 34![]() |
0.0399 | H-4 → L+1 (10%), H-3 → L+1 (29%), H-1 → L+1 (39%), H-4 → L (4%), H-2 → L (4%), H-1 → L (6%) | ||
6b | 377b | 367 | 27![]() |
0.1553 | H → L (97%) |
373d | 336 | 29![]() |
0.002 | H → L+1 (98%) | |
300c | 330 | 30![]() |
0.0282 | H-4 → L (25%), H-3 → L (20%), H-2 → L (15%), H-1 → L (33%), H-6 → L (2%) | |
307 | 32![]() |
0.1772 | H-3 → L (14%), H-2 → L (18%), H-1 → L (60%), H-4 → L (5%) | ||
298 | 33![]() |
0.0738 | H-1 → L+1 (93%) H-8 → L (2%) | ||
293 | 34![]() |
0.0043 | H-2 → L+1 (85%) H-3 → L+1 (3%) | ||
6c | 332b | 367 | 27![]() |
0.1357 | H → L (97%) |
311c | 343 | 29![]() |
0.0018 | H → L+1 (99%) | |
305d | 328 | 30![]() |
0.0131 | H-4 → L (26%), H-3 → L (33%), H-2 → L (13%), H-1 → L (22%) | |
6d | 372d | 368.198 | 27![]() |
0.120 | H → L (96%) |
365b | 350.274 | 28![]() |
0.002 | H → L+1 (98%) | |
313c | 327.391 | 30![]() |
0.019 | H-4 → L (20%), H-3 → L (38%), H-1 → L (28%), H-2 → L (8%) | |
298.863 | 33![]() |
0.125 | H-3 → L (10%), H-1 → L (45%), H-1 → L+1 (35%), H-2 → L (4%) | ||
298.517 | 33![]() |
0.195 | H-2 → L (12%), H-1 → L (20%), H-1 → L+1 (55%), H-3 → L (7%) | ||
292.103 | 34![]() |
0.008 | H-4 → L+1 (25%), H-3 → L+1 (61%), H-4 → L (3%) |
The experimental absorption maxima of 6a were found to be 332 (acetone), 305 (DMSO) and 300 (1,4-dioxane), while the TD-DFT absorption maxima were found to be 364, 342, 327 and 302 nm in the gas phase with major molecular orbital contributions HOMO → LUMO (97%), HOMO → LUMO+1 (99%), HOMO+4 → LUMO (27%) and HOMO → LUMO+1 (52%), respectively (Table 4). For 6b, the experimental absorption maxima were found to be 377 (acetone), 300 (DMSO) and 373 nm (1,4-dioxane), while the TD-DFT absorption maxima were found to be 367, 336, 329 and 307 nm in the gas phase with major molecular orbital contributions HOMO → LUMO (97%), HOMO → LUMO+1 (98%), HOMO+4 → LUMO (25%) and HOMO−1 → LUMO (60%), respectively (Table 4). Similarly, for 6c, the experimental absorption maxima were found to be 332 (acetone), 311 (DMSO) and 305 nm (1,4-dioxane), while the TD-DFT absorption maxima were found to be 367, 343 and 328 nm in the gas phase with major molecular orbital contributions HOMO → LUMO (97%), HOMO → LUMO+1 (98%) and HOMO+4 → LUMO (26%), respectively (Table 4). Further, for 6d, the experimental absorption maxima were found to be 365 (acetone), 313 (DMSO) and 372 nm (1,4-dioxane), while the TD-DFT absorption maxima were found to be 368, 350 and 327 nm in the gas phase with major molecular orbital contributions HOMO → LUMO (96%), HOMO → LUMO+1 (98%) and HOMO−1 → LUMO (28%), respectively (Table 4). The maximum absorption bands of the investigated derivatives (6a–d) are visibly redshifted, which could be because of the conjugated fused ring system and the influence of the substituents. The bands at the maximum wavelengths might be assigned to the nπ* transitions of the CC, C
N and C
O bonds of the investigated derivatives (6a–d) while the bands at lower wavelengths (∼290 nm) might be assigned to the π–π* transitions of the benzene and pyridine rings (Table 4). The UV-visible data reveal good agreement between the experimental and TD-DFT findings.
![]() | (10) |
α = 1/3(αxx + αyy + αzz) | (11) |
βtot = (βx2 + βy2 + βz2)1/2 | (12) |
βtot = [(βxxx + βxyy + βxzz)2 + (βyyy + βyzz + βyxx)2 + (βzzz + βzxx + βxyz)2]1/2 | (13) |
The first order and the second-order hyperpolarizability for 6a–d, as well as their component values, are summarized in Tables S15 and S16.†
The first order polarizability along the x direction was found to be 346, 331, 355 and 354 a.u. for 6a–d, respectively. The first order polarizability along the x direction is larger than along the y and z directions (positive directions) for all compounds, which indicates the non-uniform distribution of the charges on the molecules. The total dipole polarizability (αtotal) was found to be 238, 223, 251 and 261 a.u. for 6a–d, respectively (Table S15†). The dipole polarizability magnitudes of 6c and 6d are approximately the same but greater than those for 6a and 6b. The first order hyperpolarizability was found to be 1144.46, 1468.42, 1103.06 and 1095.34 a.u. for 6a–d, respectively (Table S16†). The first order hyperpolarizability of 6b is higher than those for 6a, 6c and 6d, which might be due to the electron withdrawing ability because of the more electronegative fluoro group. Moreover, we compared our obtained parameters for 6a–d with urea because it is frequently used as a reference molecule for comparative NLO analysis. The first order hyperpolarizability for 6a–d is remarkably greater than the value for urea (β = 43 a.u.),50 which is due to the effect of the extended conjugation in said compounds (Table S16†).
Footnote |
† Electronic supplementary information (ESI) available. CCDC 1909617–1909620. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9ra05415d |
This journal is © The Royal Society of Chemistry 2019 |