Triazenes are a unique class of polyazo compounds containing three consecutive nitrogen atoms in an acyclic arrangement and are promising NLO candidates. In the present work, a series of 15 donor-π-acceptor type vinyl coupled triazene derivatives (VCTDs) with different acceptors (-NO(2), -CN, and -COOH) have been designed, and their structure, nonlinear response, and optoelectronic properties have been studied using density functional theory and time-dependent density functional theory methods. B3LYP/6-311g(d,p) optimized geometries of the designed candidates show delocalization from the acceptor to donor through a π-bridge. Molecular orbital composition analysis reveals that HOMO is stabilized by the π-bridge, whereas acceptors play a major role in the stabilization of LUMO. Among the three acceptors, nitro derivatives are found to be efficient NLO candidates, and tri- and di-substituted cyano and carboxylic acid derivatives also show reasonably good NLO response. The effect of solvation on these properties has been studied using PCM calculations. From TDDFT calculations, the computed absorption spectra of these candidates lie in the range of 350-480 nm in the gas phase and have positive solvatochromism. The ground-state stabilization interactions are accounted from NBO calculations. In an effort to substantiate the thermal stability of the designed candidates, computations have been done to identify the weak interactions in the systems through NCI and AIM analysis. In summary, 10 out of 15 designed candidates are found to have excellent NLO and optoelectronic properties.

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Indole thiosemicarbazone ligands were prepared from indole-3-carboxaldehyde and N-(un)substituted thiosemicarbazide. The Ru(η 6 -p-cymene) complexes [Ru(η 6 -pcymene)(HL1)Cl]Cl (1) and [Ru(η 6 -p-cymene)(L2)] 2 Cl 2 (2*) were exclusively synthesized from thiosemicarbazone (TSC) ligands HL1 and HL2, and [RuCl 2 (p-cymene)] 2 . The compounds were characterized by analytical and various spectroscopic (electronic, FT-IR, 1D/2D NMR, and mass) tools. The exact structures of the compounds (HL1, HL2, 1, and 2*) were confirmed by single-crystal X-ray diffraction technique. In complexes 1 and 2*, the ligand coordinated in a bidentate neutral (1)/monobasic (2*) fashion to form a fivemembered ring. The complexes showed a piano-stool geometry around the Ru ion. While 2* existed as a dimer, 1 existed as a monomer, and this was well explained through free energy, bond parameter, and charge values computed at the B3LYP/SDD level. The intercalative binding mode of the complexes with calf thymus DNA (CT DNA) was revealed by spectroscopic and viscometric studies. The DNA (pUC19 and pBR322 DNA) cleavage ability of these complexes evaluated by an agarose gel electrophoresis method confirmed significant DNA cleavage activity. Further, the interaction of the complexes with bovine serum albumin (BSA) was investigated using spectroscopic methods, which disclosed that the complexes could bind strongly with BSA. A hemolysis study with human erythrocytes revealed blood biocompatibility of the complexes. The in vitro anticancer activity of the compounds (HL1, HL2, 1, and 2*) was screened against two cancer cell lines (A549 and HepG-2) and one normal cell line (L929). Interestingly, the binuclear complex 2* showed superior activity with IC 50 = 11.5 μM, which was lower than that of cisplatin against the A549 cancer cell line. The activity of the same complex (IC 50 = 35.3 μM) was inferior to that of cisplatin in the HepG-2 cancer cell line. Further, the apoptosis mode of cell death in the cancer cell line was confirmed by using confocal microscopy and DNA fragmentation analysis.

Two cobalt(III) Schiff base complexes, trans-[Co(salen)(DA) 2 ](ClO 4 ) ( 1 ) and trans-[Co(salophen)(DA) 2 ](ClO 4 ) ( 2 ) (where salen: N,N’-bis(salicylidene)ethylenediamine, salopen: N,N’-bis(salicylidene)-1,2-phenylenediamine, DA: dodecylamine) were synthesised and characterised using various spectroscopic and analytical techniques. The binding affinity of both the complexes with CT-DNA was explored adopting UV-visible, fluorescence, circular dichroism spectroscopy and cyclic voltammetry techniques. The results revealed that both the complexes interacted with DNA via intercalation as well as notable groove binding. Protein (BSA) binding ability of these complexes was investigated by absorption and emission spectroscopy which indicate that these complexes engage in strong hydrophobic interaction with BSA. The mode of interaction between these complexes and CT-DNA/BSA was studied by molecular docking analysis. The in vitro cytotoxic property of the complexes was evaluated in A549 (human small cell lung carcinoma) and VERO (African green monkey kidney cells). The results revealed that the complexes affect viability of the cells. AO and EB staining and cell cycle analysis revealed that the mode of cell death is apoptosis. Both the complexes showed profound inhibition of angiogenesis as revealed in in-vivo chicken chorioallantoic membrane (CAM) assay. Of the two complexes, the complex 2 proved to be much more efficient in affecting the viability of lung cancer cells than complex 1 . These results indicate that the cobalt(III) Schiff base complexes in this study can be potentially used for cancer chemotherapy and as inhibitor of angiogenesis, in general, and lung cancer in particular, for which there is need for substantiation at the level of signalling mechanisms and gene expressions.

Lithium and hydrogen bonded complexes of LiF and HF with H2CO, H2CS, and H2CSe have been investigated using higher level ab initio calculations. Extensive searches of the potential energy surfaces for equilibrium structures have been done at the Hartree−Fock level, and post Hartree−Fock calculations at MP2, MP4 levels and DFT calculations with B3LYP functional have been performed on the stable forms. 6-311++G(d,p) and 6-31++G(d,p) basis sets on H, C, O, and S and 6-311++G(d,p) basis set on Se have been employed throughout. NBO analysis of the wave functions have been done to trace the origin of various interactions that stabilize the complexes. Harmonic frequencies computed at Hartree−Fock level show that, of the 10 proposed structures, LiF and HF complexes have three and one stable forms, respectively. Potential energy surface features, structure, and stability of LiF complexes are completely different from those of HF complexes. Though it is commonly observed that lithium and hydrogen bonding interactions stabilize the complexes, the origin and nature of them is found to be different in each form and in each complex. This is well reflected in complex geometries and energetics.

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Hypercoordination in silicon has long been reviewed. Dihalogenated perhalocyclohexasilane inverse sandwich complexes (ISCs) are the only group of hypercoordinate Si complexes with anion donors that contact six neutral silicon atoms; opening prospective applications in Si self-assembled nanostructures. Hypercoordinate bonds in 16 such ISCs were studied and their anion ring interactions have been understood with respect to halides. μ(6) mode of coordination was confirmed by the presence of 6 equivalent (3,-1) bond critical points through Bader's QTAIM perspective. The presence of Lewis acid sites above and below the flat Si rings were examined through a reduced density gradient (RDG) analysis, and the ability of halide anions (X' = F, Cl, Br, I) to hypercoordinate has been understood. Role of the ring halides (X) in tuning size and acidity of Lewis sites has been addressed. While the total interaction between the two anions and the ring is quantified through EDA, each SiX' hypercoordinate bond was identified as either purely ionic or transient through QTAIM computations. CDA shows that these complexes are of donor-acceptor type with significant back-donation. The analysis shows that BrF' and IF' were found to reach maximum covalency within the group. Hence in future, tuning these ISCs for construction of nanocrystalline Si structures for optoelectronic properties can essentially utilize the collective, weak yet hypercoordinate Si in these complexes.