Sono‐chemical synthesis is safest and greener methods to fabricate valuable scaffolds in short time. Currently, we are reporting an efficient ultrasound‐based synthesis of substituted acyl‐hydrazones, single crystal analysis and DFT exploration. The substituted acyl‐hydrazones synthesis i.e 2‐((6‐chloropyridin‐2‐yl)oxy)‐N′‐((1E,2E)‐3‐phenylallylidene)acetohydrazide acetonitrile (1 : 1) (CPPAH) and (E)‐2‐((6‐chloropyridin‐2‐yl)oxy)‐N′‐(4‐methylbenzylidene)acetohydrazide (MBPAH) was accomplished utilizing sono‐chemical approach.The structures of these molecules were characterized with NMR and SC‐XRD analysis. The experimental and theoretical analysis employed to determine non‐covalent, hyper‐conjugative interactions and favorable sites for reactivity. Time‐dependent density functional theory (TD‐DFT) approach was utilized to acquire insights about FMO analysis. The global reactivity parameters established with aid of HOMO and LUMO energies. QT‐AIM and Hirshfeld analyses were computed to quantify non‐covalent interactions for both crystals. Theoretically observed structural chemistry of both crystals led to a fabulous overall agreement with obtained SC‐XRD patterns. The molecular stability and bond strengths of the aforesaid molecules were imparted owing to hyper‐conjugative interactions as well as charge delocalization process. Moreover, NBO based findings were rationalized to Hirshfeld analysis and SC‐XRD data.

Herein, we report the quantum chemical results based on density functional theory for the polarizability (α) and first hyperpolarizability (β) values of diacetylene-functionalized organic molecules (DFOM) containing an electron acceptor (A) unit in the form of nitro group and electron donor (D) unit in the form of amino group. Six DFOM 1–6 have been designed by structural tailoring of the synthesized chromophore 4,4′-(buta-1,3-diyne-1,4-diyl) dianiline (R) and the influence of the D and A moieties on α and β was explored. Ground state geometries, HOMO-LUMO energies, and natural bond orbital (NBO) analysis of all DFOM (R and 1–6) were explored through B3LYP level of DFT and 6-31G(d,p) basis set. The polarizability (α), first hyperpolarizability (β) values were computed using B3LYP (gas phase), CAM-B3LYP (gas phase), CAM-B3LYP (solvent DMSO) methods and 6-31G(d,p) basis set combination. UV-Visible analysis was performed at CAM-B3LYP/6-31G(d,p) level of theory. Results illustrated that much reduced energy gap in the range of 2.212–2.809 eV was observed in designed DFOM 1–6 as compared to parent molecule R (4.405 eV). Designed DFOM (except for 2 and 4) were found red shifted compared to parent molecule R. An absorption at longer wavelength was observed for 6 with 371.46 nm. NBO analysis confirmed the involvement of extended conjugation and as well as charge transfer character towards the promising NLO response and red shift of molecules under study. Overall, compound 6 displayed large <α> and βtot, computed to be 333.40 (a.u.) (B3LYP gas), 302.38 (a.u.) (CAM-B3LYP gas), 380.46 (a.u.) (CAM-B3LYP solvent) and 24708.79 (a.u.), 11841.93 (a.u.), 25053.32 (a.u.) measured from B3LYP (gas), CAM-B3LYP (gas) and CAM-B3LYP (DMSO) methods respectively. This investigation provides a theoretical framework for conversion of centrosymmetric molecules into non-centrosymmetric architectures to discover NLO candidates for modern hi-tech applications.

The pyridine‐based halogenated hydrazone derivatives (E)‐N′‐benzylidene‐2‐[(6″‐chloroazin‐2″‐yl)oxy]acetohydrazide (6a), (E)‐N′‐(3′‐chlorobenzylidene)‐2‐[(6″‐chloroazin‐2″‐yl)oxy]acetohydrazide (6b) and (E)‐N′‐(3′‐bromobenzylidene)‐2‐[(6″‐chloroazin‐2″‐yl)oxy]acetohydrazide (6c) have been obtained using 6‐chloro‐2‐hydroxypyridine. The structure of the products (6a–c) has been verified using X‐ray crystallography and spectroscopic approaches. A single‐crystal X‐ray diffraction (SC‐XRD) investigation showed that the structures are stabilized by intermolecular attractive forces. Additionally, density functional theory (DFT) has been adopted to explore the structural properties, vibrational spectra, noncovalent interactions and frontier molecular orbitals using the B3LYP/6‐311 + G(d,p) level. The nonlinear optical properties of the title compounds were calculated using the CAM‐B3LYP/6‐311 + G(d,p) level. Frequency analysis confirmed the stability of the molecules, and an excellent correlation was observed between the DFT‐ and SC‐XRD‐based structural parameters. The SC‐XRD analysis confirmed that the dimers of 6a, 6b and 6c are linked by hydrogen‐bonding interactions. Natural bond orbital (NBO) analysis also reconfirmed the strength of intermolecular hydrogen‐bonding and hyperconjugative interactions. NBO investigation was also utilized to analyze the atomic charges. Moreover, Fourier transform infrared and natural population analyses endorsed that there are significant N&bond;H⋅⋅⋅O&dbond;C hydrogen‐bonding linkages in dimeric structures of the compounds. The hydrogen‐bonding network and different sorts of hyperconjugative interactions are the main reasons for the stability of the products in the solid state. The highest occupied and lowest unoccupied molecular orbital energies and first‐order nonlinear optical properties of these molecules are reported. The quantum chemical parameters were derived using frontier molecular orbital energies.

Ultrasound-based synthesis at room temperature produces valuable compounds greener and safer than most other methods. This study presents the sonochemical fabrication and characterization of a pyridine-based halogenated hydrazone, (E)-2-((6-chloropyridin-2-yl)oxy)-N′-(2-hydroxybenzylidene) acetohydrazide (HBPAH). The NMR spectroscopic technique was used to determine the structure, while SC-XRD confirmed its crystalline nature. Our structural studies revealed that strong, inter-molecular attractive forces stabilize this crystalline organic compound. Moreover, the compound was optimized at the B3LYP/6-311G(d,p) level using the Crystallographic Information File (CIF). Natural bonding orbital (NBO) and natural population analysis (NPA) were performed at the same level using optimized geometry. Time-dependent density functional theory (DFT) was performed at the B3LYP/6-311G (d,p) method to calculate the frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP). The global reactivity descriptors were determined using HOMO and LUMO energy gaps. Theoretical calculations based on the Quantum Theory of Atoms in Molecules (QT-AIM) and Hirshfeld analyses identified the non-covalent and covalent interactions of the HBPAH compound. Consequently, QT-AIM and Hirshfeld analyses agree with experimental results.

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