Photophysical properties and computational investigations of tricarbonylrhenium(I)[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]L and tricarbonylrhenium(I)[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]L derivatives (X=N–CH3, O, or S; L=Cl−, pyridine)

Azo-oximate metal-carbonyl to metallocarboxylic acid via the intermediate Ir(III) radical congener: quest for co-ligand driven stability of open- and closed-shell complexes

The redox non-innocent behavior of the diaryl-azo-oxime ligand L^NOH1 has been accentuated via the synthesis of metastable anion radical complexes of type trans-[Ir(L^NO˙-)Cl(CO)(PPh₃)₂] 2 (CO is trans to azo group of the ligand) by the oxidative coordination reaction of 1 with Vaska's complex. The stereochemical role of co-ligands vis-à-vis the interplay of π-bonding has been found to be decisive in controlling the aptitude of the coordinated redox non-innocent ligand to accept or reject an electron. This has been clarified via the isolation of quite a few complexes as well as the failure to synthesize some others. The oxidized analogues of type trans-[Ir(L^NO-)Cl(CO)(PPh₃)₂]⁺2+ (CO and azo group of the ligand are trans) as well as its cis isomer cis-[Ir(L^NO-)Cl(CO)(PPh₃)₂]⁺3+ (CO and azo group of the ligand are cis) have been structurally characterized but the radical anion congener of the latter could not be synthesized. Furthermore, the closed shell complexes [Ir(L^NO-)Cl₂(PPh₃)₂] 4 and [Ir(L^NO-)₂Cl(PPh₃)] 5 have been well characterized by diffraction as well as spectral techniques but their corresponding azo anion radical complexes could not be isolated and this is attributed to the trans influence of ancillary ligands. The anion radical complexes trans-[Ir(L^NO˙-)Cl(CO)(PPh₃)₂] 2 may be rapidly transformed to the metallocarboxylic acids trans-[Ir(L^NO-)Cl(CO₂H)(PPh₃)₂] 6via a proton-coupled electron transfer (PCET) process, thereby demonstrating the role of odd electron over the coordinated ligand framework to trigger metal-mediated carbonyl to carboxylic acid functionalization. Complexes 6 are further stabilized via intramolecular -CO₂H⋯ON- (carboxylic acid⋯oximato) H-bonding. The optoelectronic properties as well as the origin of transitions in the complexes were analyzed by TD-DFT and theoretical analysis, which further disclose that the odd electron in trans-[Ir(L^NO˙-)Cl(CO)(PPh₃)₂] 2 is primarily azo-oxime centric with very low contribution from the iridium center.

Neutral Re(I) Complex Platform for Live Intracellular Imaging

Luminescent metal complexes are a valuable platform for the generation of cell imaging agents. However, many metal complexes are cationic, a factor that can dominate the intracellular accumulation to specific organelles. Neutral Re(I) complexes offer a more attractive platform for the development of bioconjugated imaging agents, where charge cannot influence their intracellular distribution. Herein, we report the synthesis of a neutral complex (ReAlkyne), which was used as a platform for the generation of four carbohydrate-conjugated imaging agents via Cu(I)-catalyzed azide-alkyne cycloaddition. A comprehensive evaluation of the physical and optical properties of each complex is provided, together with a determination of their utility as live cell imaging agents in H9c2 cardiomyoblasts. Unlike their cationic counterparts, many of which localize within mitochondria, these neutral complexes have localized within the endosomal/lysosomal network, a result consistent with examples of dinuclear carbohydrate-appended neutral Re(I) complexes that have been reported. This further demonstrates the utility of these neutral Re(I) complex imaging platforms as viable imaging platforms for the development of bioconjugated cell imaging agents.

Coligand driven diverse organometallation in benzothiazolyl-hydrazone derivatized pyrene: ortho vs. peri C–H activation

Divergent aromatic C–H activation at both ortho and peri positions in polyaromatic hydrocarbons has been successfully accomplished by suitable variation of the coligand.

Polyaromatic hydrocarbon derivatized azo-oximes of cobalt(iii) for the ligand-redox controlled electrocatalytic oxygen reduction reaction

Two new polyaromatic hydrocarbon (PAH) derivatized cobalt(iii) azo-oxime complexes were synthesized and their activity in electrocatalytic oxygen reduction reaction (ORR) were explored.

Ruthenocycles of benzothiazolyl and pyridyl hydrazones with ancillary PAHs: synthesis, structure, electrochemistry and antimicrobial activity

The antimicrobial activity of ruthenocycles of pyridyl and benzothiazolyl hydrazones has been investigated. The study established that such activity is comparatively higher for the complex containing benzothiazolyl hydrazone.

A smart molecular probe for selective recognition of nitric oxide in 100% aqueous solution with cell imaging application and DFT studies

A simple, least-cytotoxic as well as an efficient fluorescent sensor HqEN480 recognizes NO in 100% aqueous solution with cell imaging application.

Experimental and theoretical investigation of a metalloreceptor bearing a [Re(CO)3]+ core incorporating a multifunctional ligand: selective reactivity towards Zn2+ and CN− ions

Novel Re(i) complex containing multifunctional ligand HL shows selective reactivity towards Zn²⁺ and CN⁻.

Dansyl-appended CuII-complex-based nitroxyl (HNO) sensing with living cell imaging application and DFT studies

We introduce herein, a novel copper complex-based fluorescent probe[Cu^II(DQ₄₆₈)Cl]⁺that exhibits a significant fluorescence turn-on response towards nitroxyl with high selectivity over other biological reactive oxygen, nitrogen and sulfur species, including nitric oxide.

Syntheses, characterization, and electrochemical behavior of alkylated 2-(2′-quinolylbenzimidazole) complexes of rhenium (I)

A series of ClRe(CO)3-containing complexes with 1-methyl-1H-benzo[d]imidazol-2-yl)quinoline (Me-QuBIm), 1-benzyl-1H-benzo[d]imidazol-2-yl)quinoline (Bn-QuBIm), and 2-(1-(4-methoxybenzyl)-1H-benzo[d]imidazol-2-yl)quinoline (OMeBn-QuBIm) ligands were prepared and characterized. Each complex was characterized using 1H and 13C NMR, infrared, UV–vis, and fluorescence spectroscopies, and cyclic voltammetry. The physical properties of each complex are similar to the parent ClRe(CO)3(2-(1H-benzo[d]imidazol-2-yl)quinoline) complex. However, the electrochemical behavior is distinct from the parent, showing reversible voltammograms and poor CO2 reduction activity. Addition of K+ or Mg2+ as Lewis acids modestly increases catalytic currents, but at large overpotentials. The work presented here is consistent with a mechanism that involves rhenium reduction and deprotonation of imidazole and benzimidazole prior to CO2 reduction electrocatalysis.

A hydrazone based probe for selective sensing of Al(iii) and Al(iii)-probe complex mediated secondary sensing of PPi: framing of molecular logic circuit and memory device and computational studies

A hydrazone-based conjugate acts as a dual channel sensor towards Al³⁺and PPi in H₂O–MeOH with excellent sensing capability in live cells.

A novel chemosensor based on rhodamine and azobenzene moieties for selective detection of Al3+ ions

Both rhodamine and azobenzene moieties have been conjugated to prepare a novel chemosensor for the detection of Al³⁺ through CHEF-PET and the spirolactam ring opening mechanism.

Electrochemical CO2 Reduction at Glassy Carbon Electrodes Functionalized by MnI and ReI Organometallic Complexes

The catalytic activities towards electrochemical CO₂ reduction of two new rhenium and manganese complexes, namely fac-Mn(apbpy)(CO)₃ Br (1) and fac-Re(apbpy)(CO)₃ Cl (2) (apbpy=4-(4-aminophenyl)-2,2'-bipyridine), in both homogeneous and heterogeneous phases are compared. A glassy carbon electrode (GCE) surface has been functionalized with complexes 1 and 2 by two approaches: a) direct electrochemical oxidation of the amino group with formation of C-N bonds, and b) electrochemical reduction of the corresponding diazonium salts with formation of C-C bonds. The chemically modified GCEs show efficient conversion of CO₂ into CO, with turnover numbers (TONs) about 60 times higher than those of the corresponding catalysts in homogeneous solutions, and in a much shorter time.

High-Throughput Preparation of New Photoactive Nanocomposites

New low-cost photoactive hybrid materials based on organic luminescent molecules inserted into hydrotalcite (layered double hydroxides; LDH) were produced, which exploit the high-throughput liquid-assisted grinding (LAG) method. These materials are conceived for applications in dye-sensitized solar cells (DSSCs) as a co-absorbers and in silicon photovoltaic (PV) panels to improve their efficiency as they are able to emit where PV modules show the maximum efficiency. A molecule that shows a large Stokes' shift was designed, synthesized, and intercalated into LDH. Two dyes already used in DSSCs were also intercalated to produce two new nanocomposites. LDH intercalation allows the stability of organic dyes to be improved and their direct use in polymer melt blending. The prepared nanocomposites absorb sunlight from UV to visible and emit from blue to near-IR and thus can be exploited for light-energy management. Finally one nanocomposite was dispersed by melt blending into a poly(methyl methacrylate)-block-poly(n-butyl acrylate) copolymer to obtain a photoactive film.

A novel 8-hydroxyquinoline-pyrazole based highly sensitive and selective Al(iii) sensor in a purely aqueous medium with intracellular application: experimental and computational studies

A new 8-hydroxyquinoline-pyrazole based probe senses Al³⁺ and hence Al³⁺–8Q-NH-Pyz complex mediated F⁻ in a purely aqueous medium.

ESIPT blocked CHEF based differential dual sensor for Zn2+ and Al3+in a pseudo-aqueous medium with intracellular bio-imaging applications and computational studies

A novel H3SAL-NH probe exhibits ESIPT from the phenolic OH group to the azomethine N atom in the excited state. This is blocked in the presence of Zn²⁺ and Al³⁺ giving turn on fluorescence which is useful for imaging in live HepG2 cells.

Synthesis and evaluation of new salicylaldehyde-2-picolinylhydrazone Schiff base compounds of Ru(II), Rh(III) and Ir(III) as in vitro antitumor, antibacterial and fluorescence imaging agents

Reaction of salicylaldehyde-2-picolinylhydrazone (HL) Schiff base ligand with precursor compounds [{(p-cymene)RuCl2}2] 1, [{(C6H6)RuCl2}2] 2, [{Cp*RhCl2}2] 3 and [{Cp*IrCl2}2] 4 yielded the corresponding neutral mononuclear compounds 5-8, respectively. The in vitro antitumor evaluation of the compounds 1-8 against Dalton's ascites lymphoma (DL) cells by fluorescence-based apoptosis study and by their half-maximal inhibitory concentration (IC50) values revealed the high antitumor activity of compounds 3, 4, 5 and 6. Compounds 1-8 render comparatively lower apoptotic effect than that of cisplatin on model non-tumor cells, i.e., peripheral blood mononuclear cells (PBMC). The antibacterial evaluation of compounds 5-8 by agar well-diffusion method revealed that compound 6 is significantly effective against all the eight bacterial species considered with zone of inhibition up to 35 mm. Fluorescence imaging study of compounds 5-8 with plasmid circular DNA (pcDNA) and HeLa RNA demonstrated their fluorescence imaging property upon binding with nucleic acids. The docking study with some key enzymes associated with the propagation of cancer such as ribonucleotide reductase, thymidylate synthase, thymidylate phosphorylase and topoisomerase II revealed strong interactions between proteins and compounds 5-8. Conformational analysis by density functional theory (DFT) study has corroborated our experimental observation of the N, N binding mode of ligand. Compounds 5-8 exhibited a HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) energy gap 2.99-3.04 eV. Half-sandwich ruthenium, rhodium and iridium compounds were obtained by treatment of metal precursors with salicylaldehyde-2-picolinylhydrazone (HL) by in situ metal-mediated deprotonation of the ligand. Compounds under investigation have shown potential antitumor, antibacterial and fluorescence imaging properties. Arene ruthenium compounds exhibited higher activity compared to that of Cp*Rh/Cp*Ir in inhibiting the cancer cells growth and pathogenic bacteria. At a concentration 100 µg/mL, the apoptosis activity of arene ruthenium compounds, 5 and 6 (~30 %) is double to that of Cp*Rh/Cp*Ir compounds, 7 and 8 (~12 %). Among the four new compounds 5-8, the benzene ruthenium compound, i.e., compound 6 is significantly effective against the pathogenic bacteria under investigation.

Development of a multifunctional biomimicking l-cysteine based oxovanadium(iv) complex: synthesis, DFT calculations, bromo-peroxidation and nuclease activity

An oxovanadium complex [VO(sal-l-cys)(phen)] (sal-l-cys = Schiff base derived from salicylaldehyde and l-cysteine; phen = 1,10-phenanthroline) has been synthesized and characterized by spectroscopic studies (IR, UV-vis, ESI-MS and EPR studies).

Photophysical property vs. medium: mononuclear, dinuclear and trinuclear Zn(ii) complexes

Mononuclear, acetato bridged dinuclear and phenoxo bridged trinuclear Zn(ii) complexes have been synthesized. Their photophysical properties were characterized spectroscopically and with TDDFT and attributed to intra ligand (π → π*) charge transfer.

Synthesis, characterization and DFT study of oxorhenium(v) complexes incorporating quinoline based tridentate ligands

Two mononuclear Re(v) complexes were synthesized using two different O, N, N coordinating Schiff base ligands. The X-ray structure and catalytic properties of the complexes are investigated and the electronic structure and absorption spectra were also calculated.

The reasons for ligand-dependent quantum yields and spectroscopic properties of platinum(II) complexes based on tetradentate O^N^C^N ligands: a DFT and TD-DFT study

DFT and TD-DFT methods have been employed to theoretically investigate the properties of three recently synthesized green-emitting platinum(II) complexes (1-3) bearing tetradentate O^N^C^N ligands (O^C^N^C = 2-(4-(3,5-di-tert-butylphenyl)-6-(3-(pyridin-2-yl)phenyl)-pyridin-2-yl)phenolate and its derivatives) that have been testified to be good emitters in organic light-emitting diodes (OLEDs), especially for complex 3. The effect of the variation of the substituents on the electronic and optical properties is emphatically explored. Our calculation results reveal that the introduction of an electron-releasing group on one phenyl ring of the O^C^N^C ligand (complex 2) does not result in a distinct alteration of the spectra. However, the incorporation of the norbornane group to the O^C^N^C ligand (complex 3) leads to a blue-shift in the absorption and emission spectra as compared with 1. In addition, how the absorption and emission spectra are affected by the solvent polarity is studied. Both the absorption and the emission spectra display red-shifts of various degrees with the decrease of the solvent polarity. The different phosphorescent quantum yields of the three complexes are compared. It is reasonable to believe that the high (3)MLCT (metal-to-ligand charge transfer) contribution and high percentage of the metallic character (M(c), %) in the emission process, as well as the largest vertical transition energy for 3, result in the highest quantum efficiency.

A novel pyrene-2-(pyridin-2-ylmethylsulfanyl)ethylamine based turn-on dual sensor for Al3+: experimental and computational studies

A pyrene based pyrene-2-(pyridin-2-ylmethylsulfanyl)-ethylamine (PP) is found to exhibit a turn-on chemo- and fluorogenic dual sensing of Al³⁺ through PET blocking and CHEF effect.

Molecular and electronic structure of nonradical homoleptic pyridyl-azo-oxime complexes of cobalt(iii) and the azo-oxime anion radical congener: an experimental and theoretical investigation

Synthesis and optoelectronic study of Co(iii)–pyridyl-azo-oxime complexes and isolation of Co(iii)-bound azo-oxime anion radical.

Copper(ii) induced oxidative modification and complexation of a schiff base ligand: synthesis, crystal structure, catalytic oxidation of aromatic hydrocarbons and DFT calculation

A mononuclear square planar complex [Cu^II(L^2f)], formed from a Schiff baseH2Laand Cu²⁺with the concomitant oxidation of two –CH₂OH groups to aldehyde, displayed catalytic oxidation of aromatic hydrocarbons.

A light harvesting mononuclear manganese(ii) complex: synthesis, characterization, DFT and TDDFT calculations and photophysical profile

A new manganese(ii) [Mn^II(DEMP)(NCS)(H₂O)] (DEMP = Schiff base derived from salicylaldehyde and 2-diethylaminoethylamine) complex has been synthesized and characterized. The complex absorbs light ranging from 200–850 nm. Thus, the molecule is capable of harvesting the entire range of sunlight falling on earth.

A novel copper(II) complex as a nitric oxide turn-on fluorosensor: intracellular applications and DFT calculation

We report, herein, the development of an easily synthesizable novel dansyl-based turn-on NO sensor L2. The UV-Vis titration data of L2 with Cu(2+) display a gradual increase in absorbance at 418 nm with [Cu(2+)], which were analyzed by using a non-linear least-squares computer-fit program yielding K = (1.16 ± 0.36) × 10(6) M(-1) and n = (1.28 ± 0.03) indicating a 1 : 1 complexation. The ground state geometries of L2 as well as its complex [Cu(L2)Cl](+) (1) were optimized by DFT calculations which showed that in complex 1 the central metal ion is in distorted tetrahedral geometry with bond distances very close to those found in analogous Cu(2+) complexes. The fluorescence of L2 was dramatically quenched (∼60-fold) through complexation with paramagnetic Cu(2+) to form [Cu(L2)Cl](+) in MeCN-H2O (9 : 1, v/v) at pH 7.2 in HEPES buffer, which on further treatment with Angeli's salt (Na2N2O3) restores its fluorescence property by ∼15-fold due to the reduction of Cu(2+) to Cu(+) by NO generated in solution from Na2N2O3. The lifetime measurements displayed a substantial decrease in the lifetime of free ligand L2 (τ0 = 12 ns) on complexation with Cu(2+) (τ0 = 2.1 ns). The detection limit of NO calculated by the 3σ method gives a value of 1.6 nM. The NO induced fluorescence enhancement of [Cu(II)(L2)Cl](+) was due to the reduction of [Cu(II)(L2)Cl](+) (1) to [Cu(I)(L2)](+) (2) and is supported by the disappearance of the d-d transition band at 850 nm as well as the X-band EPR signal of 1. The selective "turn on" fluorogenic behavior of L2 was examined on HeLa cells of human cervical cancer origin by fluorescence microscopy which showed very intense intracellular fluorescence that was strongly suppressed by the addition of Cu(2+) but it regains its fluorescence property on further incubation with Angeli's salt (Na2N2O3). The existence of [Cu(II)(L2)Cl](+) and [Cu(I)(L2)](+) in solution was confirmed by ESI-MS(+) (m/z) analysis. The effect of different biologically relevant cations and anions on the fluorescence property of L2 indicates that it was only the [Cu(II)(L2)Cl](+) which displayed high selectivity for NO, indicating its suitability for intracellular application without much worry about its cytotoxicity in a specified dose.

DENSITY FUNCTIONAL THEORY/TIME-DEPENDENT DENSITY FUNCTIONAL THEORY STUDY ON THE STRUCTURES AND SOLVENT EFFECTS ON THE ELECTRONIC SPECTRA OF Ru(II) POLYPYRIDYL COMPLEXES: [Ru(bpy)2(L)]2+ (L = CNOIP, HPIP, DPPZ, TAPIP)

The structures and solvent dependence of electronic spectra of four Ru ( II ) polypyridyl complexes: [ Ru ( bpy )2 CNOIP ]2+, bpy = 2,2-bipyridine and CNOIP = 2-(2-chloro-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline (Ru-1); [ Ru ( bpy )2 HPIP ]2+, HPIP = 2-(2-hydroxyphenyl) imidazo[4,5-f][1,10]phenanthroline ( Ru -2); [ Ru ( bpy )2 DPPZ ]2+, DPPZ = dipyrido[3,2:a-2′,3′:c]-phenazine ( Ru -3); [ Ru ( bpy )2 TAPIP ]2+, TAPTP = 4,5,9,18-tetraazaphenanthreno-[9,10-b]triphenylene ( Ru -4) have been carried out by density functional theory/time-dependent density functional theory in vacuum and nine solvents are described by the conductor-like polarized continuum model. The calculated results show that the solvent has a strong effect on the electron distribution of molecular orbitals and character of charge transfer. In water, the simulated absorption spectra (λmax) are in accordance with experimental data. The computational results also indicate the electronic spectra of Ru ( II ) polypyridyl complexes: [ Ru ( bpy )2( L )]2+ is very sensitive to the intercalative ligands L = CNOIP, HPIP, DPPZ, TAPIP in the presence of solvent. It was noted that the trend of transition intensity of complexes strongly depends on the polarity of solvents. In the present polar solvents, the transition intensity trend of Ru -4 > Ru -1 > Ru -2 > Ru -3 was obtained, but in the case of nonpolar solvents, the transition intensity trend is Ru -4 > Ru -3 > Ru -1 > Ru -2. Among the four polypyridyl complexes, [ Ru ( bpy )2 TAPIP ]2+( Ru -4) exhibits the strongest oscillator strength in all nine solvents.