1 Introduction

Chalcones are open-chain Flavonoids in which the two aromatic rings are joined by a three-carbon chain [1]. They display a wide range of pharmacological properties, such as antibacterial [2], antifungal [3], antimutagenic [4], antimitotic and antiproliferative [5], antitumor [6], antioxidant [7], anti-inflammatory [8], antimalarial [9, 10], antileishmanial activity [10], antitubercular [11] and anti-diabetic [12]. Chalcones have attracted much attention for past decades due to the application as marine biofouling preventing agent [13], fluorescent probes [14] as conductive organic solar cells [15] and sweetening agent [16]. They are also useful in materials science fields such as nonlinear optics [17], optoelectronics [18], electrochemical sensing [19], Langmuir films and photoinitiated polymerization [20]. Because of the significant applications of chalcones here, we report the crystal structure of (2E)-3-(2, 6-dichlorophenyl)-1-(4-methoxyphenyl) prop-2-en-1-one. The compound was crystallized and its final structures were confirmed after diffracting this on single-crystal X-ray diffractometer. Along with this, we also report a combined experimental and theoretical analysis of molecular structure, vibrational and electronic spectra of the title compound. For the theoretical analysis of the title compound, density functional theory (DFT) calculations have been performed at B3LYP functional and 6-311++ G (d, p) basic set combination. The TD-DFT procedure is used to compute UV–visible spectral properties. In addition to this, the FMOs, electronic transition, global chemical reactivity descriptors are studied. The title molecule screened for antimicrobial activity.

2 Experimental

2.1 Material and physical measurement

The melting point is determined in open capillaries and is uncorrected. The purity of the compound was checked by TLC using silica gel-G coated Aluminum plates and spot visualize under UV radiation. FT-IR spectrum was recorded on Shimadzu spectrometer using KBr pellets. 1H NMR spectrum was recorded on a Brucker Avance II 500 MHz spectrometer using TMS as an Internal Standard. The electronic absorption spectrum of the title compound was recorded at room temperature in dichloromethane solution on a Shimadzu UV–Vis spectrometer working at 200–800 nm. High-resolution mass spectrometry analysis was conducted by using the ESI mode on Bruker Impact II UHR-TOF MS instrument.

2.2 Synthesis and crystal growth

Synthesis of (2E)-3-(2, 6-dichlorophenyl)-1-(4-methoxyphenyl) prop-2-en-1-one

A mixture of 4-methoxy acetophenone (1 mol) and 2, 6-dichlorobenzaldehyde (1 mol.) was dissolved in ethanol (15–20 mL) and 5 mL of KOH (20%) was added to the solution dropwise with stirring at room temperature and continue the stirring further for 4 h. The obtained product was filtered, washed with water, dried and recrystallized from ethanol. Crystals suitable for X-ray diffraction study were obtained by a slow evaporation technique using ethanol as solvent.

Yield: 92%; melting point: 182 °C; UV–Vis (λMax, nm, dichloromethane): 308; FT-IR (KBr, cm−1): 3076 (aromatic C–H), 2841 (C–H), 1656 (C=O), 1585 (C=C) 1508 (aromatic C=C), 713 (C–Cl); 1H NMR (500 MHz, CDCl3, δ/ppm): 8.04 (d, 2H, J = 7.5 Hz), 7.85 (d, 1H, J = 15.6 Hz), 7.68 (d, 1H, J = 15.6 Hz), 7.39 (d, 2H, J = 8 Hz), 7.23(t, 1H, J = 8 Hz), 6.9 (d, 2H, J = 7.5 Hz), 3.82 (s, 3H); calculated mass (m/z) for C16H12O2Cl2:307.0292 [M + H]+; HR-MS (m/z): 307.0287 [M + H]+ (Scheme 1).

Scheme 1
scheme 1

The synthetic route of the title compound

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2.3 X-ray data collection and refinement

The single crystal XRD data were collected on a Bruker D8 Venture diffractometer. Measurements were performed at 273 (2) K temperature using graphite monochromatic Cu-Kα radiation (λ = 1.54178 Å). The crystal structure was solved by using direct methods of SHELXS-14/5 and refined by full-matrix least-squares refinement methods based on F2 with SHELXL-17/1 program [21]. All non-hydrogen atoms were refined anisotropically. The molecular graphics were drawn using Ortep-3 programs [22]. The crystallographic data and refinement parameters are given in Table 1 and a selection of bond lengths and angles are shown in Table 2.

Table 1 Crystal data and structure refinement for the title compound
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Table 2 Selected experimental and theoretical geometrical parameters of title compound
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2.4 Computational details

The DFT calculations were performed using Gaussian W (03) program package [23]. The molecular geometries were optimized in the ground state by using B3LYP [24, 25] exchange–correlation functional and 6-311++ G (d, p) basis set. The Vibration frequency was calculated for optimized structure in the gas phase with the same level of theory. The DFT calculated vibrational frequencies are found to be higher than experimental vibration, to overcome this we scale the calculated frequencies by scaling factor 0.96 [26] for better agreement with experimental values. None of the predicted vibrational frequencies has an imaginary frequency. The vibrational band assignments were made using the Gauss View 4.1.2 molecular visualization program [27]. The time-dependent density functional theory (TD-DFT) [28] was performed to obtain electronic absorption spectra at B3LYP/6-311++ G (d, p) level of theory in a vacuum of the optimized structure in the ground state. From Homo Lumo energies, global reactivity parameters were calculated with the help of the standard equation to investigate the reactivity and stability of the compound.

3 Results and discussion

3.1 Crystal structure and optimized structure analysis

The molecular crystal and optimized structure of the title compound are shown in Fig. 1a, b. This compound crystallizes in the orthorhombic crystal system of P-21 21 21 space group where the unit cell parameters are a = 6.4704 (4) Å, b = 12.9304 (8) Å, c = 16.7181 (11) Å, α = 90°, β = 90°, γ = 90° and Z = 4. The numbering of atom considered from the crystal structure (Fig. 1a). The methoxy substituted groups around the phenyl rings are almost planar. The molecular structure of the title compound (Fig. 1a) shows the methoxy substituent [O(1)] at the para position of one ring [C(1)–C(13)] and dichloro substituent atoms [Cl(1) and Cl(2)] at the ortho position of another ring [(C8)–C(00d)]. In the title compound, two aromatic rings exhibit non-planar geometry and it is due to the presence of two chlorine atoms on one phenyl ring. The selected geometrical parameters are listed in Table 2. The experimental C5–C6–C7–C8 torsion angle 175 (8)° and calculated observe at 178.8 (°), confirms the molecule exhibits an E configuration concerning the C6=C7 double bond. The presence of the α-β-unsaturated ketone is indicated by the shorter experimental O2–C5 [1.221 (9) Å] and C6–C7 [1.330 (11) Å] bond lengths as seen in Table 2. The calculated O2–C5 and C6–C7 bond lengths are found to be 1.2243 Å and 1.3399 Å respectively for B3LYP. The experimental C–C bond length can be observed between 1.495 and 1.33 Å, calculated ones were between 1.4927  and 1.3399 Å (B3LYP). Experimental sp3 C–O bond length is observed between 1.4246 and 1.3574 Å, calculated ones were detected at 1.367–1.335 Å (B3LYP). The average C–Cl bond lengths of 1.732 Å and found within the expected range all bond lengths and angles are within the normal ranges and compared with previously reported structures of chalcones [29,30,31].

Fig. 1
figure 1

a Molecular structure of the compound with a 50% ellipsoids probability with the atomic numbering scheme. b Optimized structure of (2E)-3-(2,6-dichlorophenyl)-1-(4-methoxyphenyl) prop-2-en-1-one

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3.2 Mulliken atomic charges

Mulliken atomic charges calculated and reported in Table 3. Mulliken atomic charge calculation has an important role in the application of quantum chemical calculations to Molecular system because of atomic charge effects dipole moment, electronic structure and some other properties of the molecular system [32, 33]. As indicated in Table 3, the C5 atom carries the largest positive charge (1.852333) among the other carbon atoms, therefore, expected to be the site for nucleophilic attack in the title compound. However, C9 and C11 atoms carry the highest negative charge − 1.353074, − 1.240575, respectively amongst all carbon atoms. However, except hydrogen H8 all hydrogen carries a positive charge.

Table 3 Mulliken atomic charges for title compound at B3LYP/6-311++ G (d, p) level
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3.3 FT-IR spectrum analysis

The FT-IR spectrum has been recorded in the region of 4000–500 cm−1 (solid phase) and the spectrum is shown in Fig. 2a. The calculated vibrational spectrum in the gas phase is shown in Fig. 2b. The molecule possesses C1 symmetric. There are 32 atoms in title molecule corresponding 90 fundamental modes of vibrations calculated at B3LYP/6-311++ G (d, p) level. Some of the theoretical and experimental vibrations with intensity and their assignments are represented in Table 4. The carbonyl stretching vibrations in Chalcones generally appear in the region 1750–1600 cm−1 [29]. We assign carbonyl stretching, vibration in the experimental spectrum at 1656 cm−1 and theoretically at 1650 cm−1. These values agree with previously reported values of Chalcones derivatives [30, 31]. The C-H stretching vibrations of aromatic and vinyl groups were normally seen in the region above 3000 cm−1 [34]. These vibrations are calculated in the range of 3097–3073 cm−1 and experimentally it observed at 3076 cm−1 as a mixed vibrational band. In-plane and out of plane C-H bending vibrations aromatic ring and vinyl group observe at 1255, 900, 829, 775 cm−1 (Table 4) and calculated at 1267, 877, 814, 790 cm−1. In the previously reported literature on Chalcones derivatives stretching frequency of the C=C of enone, part was observed at 1592 cm−1 and calculated at 1588 cm−1 [30]. Here in the title molecule, this vibration is computed at 1589 cm−1 and experimentally shown at 1585 cm−1. The aromatic C=C stretching vibration for the title compound observed at 1508 cm−1 and theoretically assign at 1522 cm−1. Out of plane bending vibration at 977 cm−1 indicates the Trans geometry of alkene. In the present study, C–Cl stretching vibrations were observed at 713 cm−1 and calculated at 729 cm−1. The peaks due to asymmetric and symmetric methyl stretching modes commonly observed at 2965 and 2880 cm−1 [35]. The methyl group stretching vibrations calculated in the range of 3013–2891 cm−1 are shown in Table 4. In experimental FT-IR, symmetric stretching vibration mode of the methyl group is observed at 2841 cm−1. Asymmetric and symmetric deformation of methyl group normally appears in the region of 1465–1440 cm−1 and 1390–1370 cm−1 respectively [36, 37]. In the present case methyl group deformation calculated at 1417 cm−1and observe at 1421 cm−1.

Fig. 2
figure 2

a Experimental FT-IR spectrum of the title compound. b Simulated FT-IR spectrum of the title compound in the gas phase

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Table 4 Selected experimental and theoretical vibrational assignment for the title compound calculated at B3LYP/6-311++ G (d, p) level
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3.4 Electronic spectra analysis

The electronic transitions in the UV–visible spectrum of title compound have been studied by the time-dependent density functional theory (TD-DFT) where allowed transitions are calculated in the gas phase. The electronic absorption spectrum of title molecule recorded experimentally in dichloromethane (DCM) solvent. The calculated electronic transitions of high oscillatory strength, wavelength and experimentally determined wavelength are given in Table 5. Simulated spectrum is illustrated in Fig. 3a and experimental in Fig. 3b Computed UV–visible spectrum exhibited two intense allowed transitions at λ max = 337 nm, f = 0.4422 and λ = 301 nm, f = 0.2468. Which have corresponded to the experiment λ max value of 308 nm. The observed peak in theoretical spectra indicated redshift as compared with experimental ones, so the assigned bands were characterized by (n → π*) and (π → π*) transitions. In HOMO, a π bonding electron is spread over phenyl ring, carbonyl oxygen atom and C=C moiety. In LUMO, electrons it is spread to the entire molecule except for the methyl group.

Table 5 The excitation energy (eV), oscillator strength, wavelength (nm) calculated using TD-DFT method in vacuum and experimental wavelength in dichloromethane solvent
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Fig. 3
figure 3

a Simulated UV–visible absorption spectra for the title compound computed at B3LYP/6-311++ G (d, p) level of theory in vacuum. b The experimental UV–visible absorption spectra for the title compound in dichloromethane

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3.5 HOMO–LUMO and global chemical reactivity descriptor

The highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO) are called Frontier molecular orbitals (FMOs). The HOMO, LUMO energy value and energy gap values for title compound were computed at TD-DFT/ B3LYP/6-311++ G (d, p) level of theory in the gas phase. The HOMO–LUMO Plot for the title compound in the gas phase is shown in Fig. 4. The HOMO represents the ability to donate electrons, whereas LUMO as an electron acceptor [38]. The computed gas phase HOMO and LUMO energies are − 6.55767 eV and − 2.466711 eV respectively, whereas the energy gap is found 4.09096 eV. The quantum chemical parameters such as ionization potential (I), electron affinity (A), chemical hardness (ɳ), chemical softness (S), electronic chemical potential (μ), global electrophilicity index (ω), are used to predict the reactivity and stability of the compound. On the basis of Koopman’s theorem [39], all these parameters were calculated from HOMO–LUMO energy using Eqs. 1–4 [40,41,42,43].

$$\upeta = {\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}\left( {{\text{I}}{-}{\text{A}}} \right)$$
(1)
$${\text{S}} = 1/\upeta$$
(2)
$$\upmu = - {\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}\left( {{\text{I}} + {\text{A}}} \right)$$
(3)
$$\upomega =\upmu ^{2} /2\upeta$$
(4)
Fig. 4
figure 4

The HOMO–LUMO plot of title compound obtained at B3LYP/6-311G++ (d, p) level

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where I and A are ionization potential and electron affinity of the compound respectively (I = − εHOMO) and (A = − εLUMO). The HOMO, LUMO energies and global reactivity parameters are listed in Table 6. From the calculation, it was found that the title compound is kinetically stable with the hardness value of 2.04548 eV. The chemical softness of 0.488 eV, the chemical potential of  − 4.51219 eV and the electrophilicity index of 4.97654 eV suggest that title compound possesses excellent chemical strength and stability.

Table 6 Global chemical reactivity indices for the title compound calculated at B3LYP/6-311G++ (d, p) level
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3.6 Antimicrobial activities of the synthesized compound

The newly synthesized compound (2E)-3-(2,6-dichlorophenyl)-1-(4-methoxyphenyl) prop-2-en-1-one were screened for their antimicrobial activities in vitro against Staphylococcus aureus, Bacillus subtillis, Escherichia coli and Salmonella Typhi Pathogenic bacteria and three fungi Aspergillus Niger, Aspergillus flavus, Candida albicans. The activities of the titled compound were tested using the agar diffusion method [44]. The antibiotic Penicillin (25 µg/mL) used as a reference drug for antibacterial activity and Nystatin (25 µg/mL) for antifungal activities. The dimethyl sulphoxide (1% DMSO) was used a control without compound.

The culture strains of bacteria were maintained on a nutrient agar slant at 37 ± 0.5 °C for 24 h. The antibacterial activity was evaluated using nutrient agar plate seeded with 0.1 mL of respective bacterial culture stain suspension Prepared in sterile saline (0.85%) of 105 CFU/mL dilution. The well of 6 mm diameter was filled with 0.1 mL of a compound solution of concentration 25 to 150 µg/mL separately for each bacterial strain. All the plates were incubated at 37 ± 0.5 °C for 24 h. The zone of inhibition of compound in mm was noted and minimum inhibitory concentration (MICs) was noted.

For antifungal activity, all the culture strains of fungi maintain on potato dextrose agar (PDA) slant at 27 ± 0.2 for 24–48 h till sporulation. Spores of strains were transferred into 5 mL of sterile distilled water containing 1% Tween-80 (to suspend the spore properly). The spores were counted by haemocytometer (106 CFU/mL). The sterile PDA plate was prepared to contain 2% agar, 0.1 mL of each fungal spore suspension was spread on each plate and incubated at 27 ± 0.2 °C for 12 h. After incubation well prepared using sterile cork borer and each agar well was filled with 0.1 mL of compound solution at concentration 25 to 150 µg/mL. The Plates were kept in the refrigerator for 20 min for diffusion and then incubated at 27 ± 0.2 °C for 24–28 h. After incubation, the zone of inhibition of the compound was measured in mm along with standard and minimum inhibitory concentration (MICs) were noted.

The results of antimicrobial activity are given in Table 7. From the result of antimicrobial data, the compound was found moderately active against bacteria Subtillis, E. coli. The Compound does not show promising activity against all other Bacteria. The compound also exhibits moderate activity against all fungi as compared to standard.

Table 7 Antimicrobial activity of synthesized compound
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4 Conclusion

The title compound (2E)-3-(2,6-dichlorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one has been synthesized and characterized by IR, HR-MS, 1H NMR method. Its three-dimensional structure was obtained by single-crystal XRD. The experimental and theoretical study confirmed that the molecule exhibits an E configuration. Theoretically calculated bond length, bond angle and λmax (UV spectrum) show good agreement with experimental results. The HOMO–LUMO energy gap is in good agreement with experimental results. FT-IR spectra of the title molecule show good correlation with theoretically assigned vibrational modes. The electronic spectral properties of the studied compound were calculated by the TD-DFT method. The chemical reactivity parameters indicate that the title compound possesses excellent chemical strength and stability. The compounds exhibited moderate antimicrobial activity against bacteria B. Subtillis, E. coli and all tested fungus as compared with their standards used.

5 Supplementary information

Crystallographic data are available on htttp://www.ccdc.cam.ac.uk upon request quoting deposition number CCDC 1988019 for the (2E)-3-(2, 6-dichlorophenyl)-1-(4-methoxyphenyl)-prop-2-en-1-one.