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The present study elaborates on the synthesis, crystal structure, and computational studies of two new ionic liquids. In the crystal structure, [C5H12N][C21H14ClN2O2S] (4a), the anions form chains along the a-axis direction through C—H···π(ring) interactions. These are connected into layers that run approximately parallel to the ac plane by a variety of hydrogen bonds. In the compound structure, [C5H12N][C18H15N2O2S] (4b), the two ions are primarily associated by an N—H···N hydrogen bond. In the crystal structure, layers parallel to the bc plane are formed by pairs of C—H···O and N—H···S hydrogen bonds and by C—H···π(ring) interactions. A theoretical study reveals that 4a has lower energy than 4b and is more stable. The NBO and DOS studies further confine the liquids’ structural reactivity and electronic properties. The quantum theory of atoms in a molecule (QTAIM) analysis reveals the important non-covalent interactions among the fragments and charge transfer. The global reactivity descriptors indicate their molecular reactivity relationship with the presence of functional groups. The remarkable polarizability (αo) and hyperpolarizability (βo) values indicate their optical and nonlinear optical (NLO) properties. Furthermore, the analysis performed by CrystalExplorer shows the intermolecular interactions and reactive sites between cations and anions in ionic liquids. The 2D fingerprint plots and Hirshfeld surfaces indicate the major interactions of crystals with neighboring elements in crystal packing. For both compounds, the H···H interactions are significantly higher than the other element interactions.

In the present work, we describe the synthesis of new tetrahydroisoquinoline derivatives and the crystal structures of two of them. Density functional theory (DFT) investigations at the B3LYP/6-31+G(d,p) level provided their structural reactivity and nonlinear optical properties. The low HOMO-LUMO gaps (EH-L) suggest a soft nature and higher reactivity, while calculated global reactivity descriptors provide assessments of their reactivity and electronic stability. The calculated natural bonding molecular orbital (NBO) charges show excellent charge separation (charge transfer) and identify the donor and acceptor parts of the molecules. Density of states (DOS) analyses show the newly generated energy states and reduced band gaps, which impart higher conductive properties. For surface reactivity, 3D MESP surfaces are plotted and show electron-rich sites near the nitrogen atoms of the tetrahydroisoquinoline rings. Nonlinear optical (NLO) properties of the crystals are predicted from calculated polarizability (αo) and hyperpolarizability (βo) values. For IVb, the αo and βo values are 415.53 and 1003.44 au. The remarkable value (1003.44 au) of the hyperpolarizability (βo) shows IVb has excellent NLO properties. Structural activity relationship analysis suggests that nitric oxide synthases are better targets for both compounds, and they were further subjected to molecular docking simulations to understand the binding efficiency. In addition, ADMET analyses were carried out to understand the potential activity of the molecules as drug candidates.

The multicomponent reaction of 4-nitrobenzaldehyde with acetophenone and urea in the presence of HCl was investigated, and, as a result, 4,5-bis(4-nitrophenyl)-8a-phenyl-decahydro-[1,3]diazino[4,5-d]pyrimidine-2,7-dione was synthesized. The structure of the synthesized compound was confirmed by the X-ray method. We performed Hirshfeld surfaces (HS) analysis and two-dimensional (2D) fingerprint plots for the studied compound to obtain surface reactivity and intermolecular interactions. The H∙∙∙H interactions were found to be higher, up to 32.2%, while the percentage C∙∙∙O contact was found to be the lowest among the reported interactions for single crystal packing. The energy framework analysis shows the strength of interaction energy within fragments of a single crystal at 3.08 A distances. The DFT study shows structural reactivity and a reduced HOMO-LUMO gap up to 4.0 eV. The NPA study reveals the reactivity and excellent charge transfer within the structure. The TD-DFT study reveals the absorbance in the UV region and excited state parameters during crucial transitions (transitions with maximum oscillator strength). The investigated compound shows excellent optical and nonlinear optical (NLO) properties, as indicated by its polarizability (αo) and hyperpolarizability (βo) values.

Carbon-based polynuclear clusters are designed and investigated for geometric, electronic, and nonlinear optical (NLO) properties at the CAM-B3LYP/6-311++G(d,p) level of theory. Significant binding energies per atom (ranging from −162.4 to −160.0 kcal mol−1) indicate excellent thermodynamic stabilities of these polynuclear clusters. The frontier molecular orbital (FMOs) analysis indicates excess electron nature of the clusters with low ionization potential, suggesting that they are alkali-like. The decreased energy gaps (EH-L) with increased alkali metals size revael the improved electrical conductivity (σ). The total density of state (TDOS) study reveals the alkali metals’ size-dependent electronic and conductive properties. The significant first and second hyperpolarizabilities are observed up to 5.78 × 103 and 5.55 × 106 au, respectively. The βo response shows dependence on the size of alkali metals. Furthermore, the absorption study shows transparency of these clusters in the deep-UV, and absorptions are observed at longer wavelengths (redshifted). The optical gaps from TD-DFT are considerably smaller than those of HOMO-LUMO gaps. The significant scattering hyperpolarizability (βHRS) value (1.62 × 104) is calculated for the C3 cluster, where octupolar contribution to βHRS is 92%. The dynamic first hyperpolarizability β(ω) is more pronounced for the EOPE effect at 532 nm, whereas SHG has notable values for second hyperpolarizability γ(ω).