3-Polythiophene Acetic Acid Nanosphere Anchored Few-Layer Graphene Nanocomposites for Label-Free Electrochemical Immunosensing of Liver Cancer Biomarker.

This study devised a label-free electrochemical immunosensor for the quantitative detection of alpha-fetoprotein (AFP). 3-Polythiophene acetic acid (3-PTAA) nanoparticles were anchored onto a few-layer graphene (FLG) nanosheet, and the resulting nanocomposite was utilized as the immunosensor platform. The AFP antibody (anti-AFP) was immobilized on 3-PTAA@FLG via a covalent interaction between the amine group of anti-AFP and the carboxylic group of 3-PTAA via ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling. FLG is largely responsible for providing electrochemical signals, whereas 3-PTAA nanoparticles are well-known for their ability to be compatible with biological molecules in neutral aqueous solutions. Moreover, the carboxyl group present in 3-PTAA effectively binds anti-AFP through EDC/NHS conjugation. Owing to good dispersibility and higher surface area of 3-PTAA, it is very convenient for casting the polymer directly on the electrode substrate followed by immobilization of anti-AFP. Thus, it is feasible to regulate the activity of AFP proteins and control the spatial distribution of the immobilized anti-AFP proteins. The electrochemical sensing performance was assessed via cyclic voltammetry and electrochemical impedance spectroscopy. For an increase in the bioconjugate concentration, the results demonstrated a surge in charge-transfer resistance and a consequent decline in the current response. This approach effectively detected AFP at an extended dynamic range of 0.0001-250 ng/mL with a detection limit of 0.047 pg/mL. Furthermore, the sensing capacity of the immunosensor for AFP detection has been demonstrated to be steady in real human serum cultures. Our approach exhibits good electrochemical performance in terms of reproducibility, selectivity, and stability, which would surely impart budding applications in the clinical diagnosis of several other tumor markers.

Asymmetric fabrication and in vivo evaluation of the wound healing potency of electrospun biomimetic nanofibrous scaffolds based on collagen crosslinked modified-chitosan and graphene oxide quantum dot nanocomposites.

Asymmetric scaffolds were developed through electrospinning by utilizing biocompatible materials for effective wound healing applications. First of all, the chitosan surface was modified with decanoyl chloride and crosslinked with collagen to synthesize collagen crosslinked modified-chitosan (CG-cross-CS-g-Dc). Then, the asymmetric scaffolds were fabricated through electrospinning, where the top layer was a monoaxial nanofiber of the PCL/graphene oxide quantum dot (GOQD) nanocomposite and the bottom layer was a coaxial nanofiber having PCL in the core and the CG-cross-CS-g-Dc/GOQD nanocomposite in the shell layer. The formation of monoaxial (∼130 ± 50 nm) and coaxial (∼320 ± 40 nm) nanofibers was confirmed by transmission electron microscopy (TEM). The presence of GOQDs contributed to antioxidant and antimicrobial efficacy. These scaffolds showed substantial antibacterial activity against the common wound pathogens Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The scaffolds exhibited excellent cytocompatibility (MTT assay) and anti-inflammatory behaviour as analysed via the cytokine assay and biochemical analysis. The in vivo wound healing potential of the nanofibrous scaffolds was assessed with full-thickness excisional wounds in a rat model. The scaffolds accelerated the re-epithelialization as well as the collagen deposition, thereby facilitating the wound healing process in a very short span of time (10 days). Both in vitro and in vivo analyses thus provide a compelling argument for the use of these scaffolds as therapeutic biomaterials and their suitability for application in rapid wound regeneration and repair.

Transition metal dichalcogenides nanomaterials based piezocatalytic activity: recent progresses and outlook.

Piezoelectric materials have drawn significant attention from researchers in the recent past as the piezo-potential, induced by applied external stress, generates an electric field, which paves the way for the creation and transfer of electrons and holes. After the theoretical prediction of the existence of the piezoelectric effect in transition metal dichalcogenides (TMDCs) semiconductors, intense research efforts have been made by various researchers to demonstrate the effect experimentally. In addition 2D TMDCs exhibit layer-dependent tunable electronic structure, strongly bound excitons, enhanced catalytic activity at their edges, and novel spin/pseudospin degrees of freedom. The edge sites and activated basal planes of 2D TMDCs are shown to be highly active toward catalysis of the hydrogen evolution reaction (HER). However, as compared to electrocatalytic or even photocatalytic performances, TMDC materials exhibit poorer piezocatalytic activity, in general. Therefore, a numbers of research strategies have been made to intensify the piezoelectric effect by synthesizing different types of TMDC nanostructures, by coupling the piezoelectric effect with the photocatalytic effect, by doping with other materials, etc. This review discusses various techniques of synthesis of TMDCs nanostructures and the recent progresses in applications of TMDC nanomaterials in piezocatalysis. In the present article, the piezocatalytic dye degradation performances and HER activity using different TMDCs have been reviewed in detail. Different methods of increasing the piezocatalytic activity of various TMDCs nanostructures have been illustrated. Here, it has also been attempted to systematically summarize and provide an outlook of the charge transfer behaviour and catalytic mechanisms in large varieties of TMDC piezocatalysts and piezo-photocatalysts. In addition, advanced applications of TMDC piezocatalytic materials as piezoelectric nanogenerator, piezocatalytic dye degradation, piezo-phototronic dye degradation and HER studies have been highlighted.

Catalytic dye degradation by novel phytofabricated silver/zinc oxide composites.

Phytofabrication of the nanoparticles with exotic shape and size is an attractive area where nanostructures with noteworthy physicochemical and optoelectronic properties that can be significantly employed for photocatalytic dye degradation. In this study a medicinal plant, Plumbago auriculata leaf extract (PALE) was used to synthesize zinc oxide particles (ZnOPs) and silver mixed zinc oxide particles (ZnOAg1Ps, ZnOAg10Ps, ZnO10Ag1Ps) by varying the concentration of the metal precursor salts, i.e. zinc acetate and silver nitrate. The PALE showed significantly high concentrations of polyphenols, flavonoids, reducing sugar, starch, citric acid and plumbagin up to 314.3 ± 0.33, 960.0 ± 2.88, 121.3 ± 4.60, 150.3 ± 3.17, 109.4 ± 2.36, and 260.4 ± 8.90 µg/ml, respectively which might play an important role for green synthesis and capping of the phytogenic nanoparticles. The resulting particles were polydispersed which were mostly irregular, spherical, hexagonal and rod like in shape. The pristine ZnOPs exhibited a UV absorption band at 352 nm which shifted around 370 in the Ag mixed ZnOPs with concomitant appearance of peaks at 560 and 635 nm in ZnO10Ag1Ps and ZnOAg1Ps, respectively. The majority of the ZnOPs, ZnOAg1Ps, ZnOAg10Ps, and ZnO10Ag1Ps were 407, 98, 231, and 90 nm in size, respectively. Energy dispersive spectra confirmed the elemental composition of the particles while Fourier transform infrared spectra showed the involvement of the peptide and methyl functional groups in the synthesis and capping of the particles. The composites exhibited superior photocatalytic degradation of methylene blue dye, maximum being 95.7% by the ZnOAg10Ps with a rate constant of 0.0463 s-1 following a first order kinetic model. The present result clearly highlights that Ag mixed ZnOPs synthesized using Plumbago auriculata leaf extract (PALE) can play a critical role in removal of hazardous dyes from effluents of textile and dye industries. Further expanding the application of these phytofabricated composites will promote a significant complementary and alternative strategy for treating refractory pollutants from wastewater.

Leucophyllum frutescens mediated synthesis of silver and gold nanoparticles for catalytic dye degradation.

The application of nanotechnology is gaining worldwide attention due to attractive physico-chemical and opto-electronic properties of nanoparticles that can be also employed for catalytic dye degradation. This study reports a phytogenic approach for fabrication of silver (AgNPs) and gold nanoparticles (AuNPs) using Leucophyllum frutescens (Berl.) I. M. Johnst (Scrophulariaceae) leaf extract (LFLE). Development of intense dark brown and purple color indicated the synthesis of AgNPs and AuNPs, respectively. Further characterization using UV-visible spectroscopy revealed sharp peak at 460 nm and 540 nm for AgNPs and AuNPs, respectively that were associated to their surface plasmon resonance. High resolution transmission electron microscope (HRTEM) revealed the spherical shape of the AgNPs, whereas anisotropic AuNPs were spherical, triangular and blunt ended hexagons. The majority of the spherical AgNPs and AuNPs were ∼50 ± 15 nm and ∼22 ± 20 nm, respectively. Various reaction parameters such as, metal salt concentration, temperature and concentration of the leaf extract were optimized. Maximum synthesis of AgNPs was obtained when 5 mM for AgNO3 reacted with 10% LFLE for 48 h at 50°C. Likewise, AuNPs synthesis was highest when 2 mM HAuCl4 reacted with 10% LFLE for 5 h at 30°C. Energy dispersive spectroscopy (EDS) showed phase purity of both the nanoparticles and confirmed elemental silver and gold in AgNPs and AuNPs, respectively. The average hydrodynamic particles size of AgNPs was 34.8 nm while AuNPs was 140.8 nm as revealed using dynamic light scattering (DLS) that might be due to agglomeration of smaller nanoparticles into larger clusters. ZETA potential of AgNPs and AuNPs were 0.67 mV and 5.70 mV, respectively. X-ray diffraction (XRD) analysis confirmed the crystallinity of the nanoparticles. Fourier transform infrared spectroscopy (FTIR) confirmed that various functional groups from the phytochemicals present in LFLE played a significant role in reduction and stabilization during the biogenic synthesis of the nanoparticles. The bioreduced AgNPs and AuNPs catalytically degraded Rhodamine B dye (RhB) in presence of UV-light with degradation rate constants of 0.0231 s-1 and 0.00831 s-1, respectively. RhB degradation followed a first order rate kinetics with 23.1 % and 31.7% degradation by AgNPs and AuNPs, respectively.

Syntheses of flower and tube-like MoSe2 nanostructures for ultrafast piezocatalytic degradation of organic dyes on cotton fabrics.

The synthesis of few-layered transition metal dichalcogenides (TMDCs) with abundant exposure of the active site, viz., is an important key to achieve excellent dye degradation performance. Here, we have reported synthesis and ultrafast dye degradation performance of flowers-like MoSe2 nanostructure (FMN) with ~230 nm in diameter and its transformation to tube-like MoSe2 microstructure (~1 µm in length) by tuning the solvothermal reaction time. The piezoelectric devices are developed using the FMNs delivers the highest open-circuit voltage of ~ 2.12 V, which is ~21 times higher than that of the developed device with the tube-like MoSe2 microstructure. The piezoelectric property of the synthesized samples has been judiciously utilized further for ultrafast degradation of organic dyes within 60-120 s only under the low-frequency (40 kHz) ultrasonication vibration in the dark. The estimated dye degradation efficiencies of the FMNs-based piezocatalyst are found to be ∼86% and 85% for degradation of Rhodamine B (RhB) and methylene blue (MB) dye within the 60 s, respectively. Also, the FMN has exhibited an excellent piezocatalytic dye degradation capability for RhB-MB dye mixture and dye loaded on a cotton fabric with an efficiency of ~98% (60 s) and 84% (120 s), respectively. The piezocatalytic dye degradation mechanism of FMNs has also been explained theoretically.

Antimicrobial Synergy of Silver-Platinum Nanohybrids With Antibiotics.

Various bacterial pathogens are responsible for nosocomial infections resulting in critical pathophysiological conditions, mortality, and morbidity. Most of the bacterial infections are associated with biofilm formation, which is resistant to the available antimicrobial drugs. As a result, novel bactericidal agents need to be fabricated, which can effectively combat the biofilm-associated bacterial infections. Herein, for the first time we report the antimicrobial and antibiofilm properties of silver-platinum nanohybrids (AgPtNHs), silver nanoparticles (AgNPs), and platinum nanoparticles (PtNPs) against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. The AgPtNHs were synthesized by a green route using Dioscorea bulbifera tuber extract at 100°C for 5 h. The AgPtNHs ranged in size from 20 to 80 nm, with an average of ∼59 nm. AgNPs, PtNPs, and AgPtNHs showed a zeta potential of -14.46, -1.09, and -11.39 mV, respectively. High antimicrobial activity was observed against P. aeruginosa and S. aureus and AgPtNHs exhibited potent antimicrobial synergy in combination with antibiotics such as streptomycin, rifampicin, chloramphenicol, novobiocin, and ampicillin up to variable degrees. Interestingly, AgPtNHs could inhibit bacterial biofilm formation significantly. Hence, co-administration of AgPtNHs and antibiotics may serve as a powerful strategy to treat bacterial infections.

Homo- and Heterobimetallic Ruthenium(II) and Osmium(II) Complexes Based on a Pyrene-Biimidazolate Spacer as Efficient DNA-Binding Probes in the Near-Infrared Domain.

We report in this work a new family of homo- and heterobimetallic complexes of the type [(bpy)2M(Py-Biimz)M'(II)(bpy)2](2+) (M = M' = Ru(II) or Os(II); M = Ru(II) and M' = Os(II)) derived from a pyrenyl-biimidazole-based bridge, 2-imidazolylpyreno[4,5-d]imidazole (Py-BiimzH2). The homobimetallic Ru(II) and Os(II) complexes were found to crystallize in monoclinic form with space group P21/n. All the complexes exhibit strong absorptions throughout the entire UV-vis region and also exhibit luminescence at room temperature. For osmium-containing complexes (2 and 3) both the absorption and emission band stretched up to the NIR region and thus afford more biofriendly conditions for probable applications in infrared imaging and phototherapeutic studies. Detailed luminescence studies indicate that the emission originates from the respective (3)MLCT excited state mainly centered in the [M(bpy)2](2+) moiety of the complexes and is only slightly affected by the pyrene moiety. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations in the positive potential window and several reduction processes in the negative potential window. An efficient intramolecular electronic energy transfer is found to occur from the Ru center to the Os-based component in the heterometallic dyad. The binding studies of the complexes with DNA were thoroughly studied through different spectroscopic techniques such as UV-vis absorption, steady-state and time-resolved emission, circular dichroism, and relative DNA binding study using ethidium bromide. The intercalative mode of binding was suggested to be operative in all cases. Finally, computational studies employing DFT and TD-DFT were also carried out to interpret the experimentally observed absorption and emission bands of the complexes.

Design of Multichannel Osmium-Based Metalloreceptor for Anions and Cations by Taking Profit from Metal-Ligand Interaction and Construction of Molecular Keypad Lock and Memory Device.

A polypyridylimidazole-based bifunctional Os(II) complex of the type [(bpy)2Os(tpy-Hbzim-dipy)](ClO4)2 (1), where tpy-Hbzim-dipy = 4'-[4-(4,5-dipyridin-2-yl-1H-imidazol-2-yl)-phenyl]-2,2';6',2″-terpyridine and bpy = 2,2'-bipyridine, has been synthesized and structurally characterized for the construction of multifunctional logic devices. After coordination of an [Os(bpy)2](2+) unit to one of the two bidentate chelating sites, the complex offers a terpyridine motif for binding with cationic guests and an imidazole moiety for interacting with selective anionic species. Consequently, the anion- and cation-binding aspects of the metallorecptor were examined in solution and in the solid state by different spectroscopic and electrochemical methods. The complex behaves as a bifunctional sensor for F(-), AcO(-), CN(-), Fe(2+), and Cu(2+) ions in acetonitrile, whereas it is a highly selective chromogenic chemosensor for only CN(-) and Fe(2+) ions in water. Based on various output signals with a particular set of anionic and cationic inputs, the complex mimics the functions of two-input INHIBIT, OR, NOR, and XNOR logic gates, as well as three-input NOR logic behavior. More importantly, the complicated functions of a keypad lock and memory device were also nicely demonstrated by the complex. Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations also provide a rationale for properly understanding and interpreting the experimentally observed results.

Pyrene-biimidazole based Ru(II) and Os(II) complexes as highly efficient probes for the visible and near-infrared detection of cyanide in aqueous media.

Two pyrenyl-biimidazole based mononuclear Ru(II) and Os(II) complexes of the type [(bpy)2M(Py-BiimzH2)](2+) (M = Ru(II) and Os(II)), where Py-BiimzH2 = 10-(1-H-imidazole-2-yl)-9H-pyreno[4,5-d]imidazole and bpy = 2,2'-bipyridine, have been synthesized and thoroughly characterized in this work using various analytical tools and spectroscopic techniques. These complexes were designed to recognize and sense cyanide ions in pure aqueous media. The single crystal X-ray structure of the Ru(II) complex shows that the compound is crystallized in a monoclinic system with the P2(1)/c space group. Both complexes show intense absorptions throughout the entire UV-vis region and also exhibit luminescence at room temperature. In case of Os(II), both the absorption and emission bands stretched up to the NIR region and thus a more bio-friendly condition for the detection of the anions is provided. Both steady state and time-resolved studies suggest that the emission originates predominantly from the (3)MLCT excited state mainly centered in the [M(bpy)2](2+) moiety of the complexes which is only slightly affected by the pyrene moiety. The electrochemical properties of the complexes are characterized using one reversible metal-centered oxidation and several ligand-centered reduction processes. The anion sensing properties of the complexes in both acetonitrile and pure aqueous media were thoroughly examined through different channels such as absorption, steady state and time-resolved emission spectroscopic methods and cyclic and square wave voltammetric measurements. Both complexes possess a very high selectivity towards cyanide ions in aqueous media in the presence of an excess of other anions. Moreover, the complexes display a visual detection of cyanide ions with a very low detection limit of the order of 10(-8) M. Finally, theoretical calculations employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were carried out to elucidate the details of the electronic structure and transitions involved in the complexes and their cyanide adducts.

Pyrene and imidazole functionalized luminescent bimetallic Ru(II) terpyridine complexes as efficient optical chemosensors for cyanide in aqueous, organic and solid media.

We report in this work the anion recognition and sensing aspect of a new family of bimetallic Ru(ii) complexes derived from a symmetrical bridging 5,11-bis(4-([2,2':6',2''-terpyridine]-4'-yl)phenyl)-4,12-dihydropyreno[4,5-d:9,10-d']diimidazole (tpy-H2PhImzPy-tpy) terpyridine ligand in solution as well as in the solid sate through different channels such as absorption, steady state and time-resolved emission, and (1)H NMR spectroscopic techniques. Interestingly, the complexes exhibit luminescence in the red region with moderately long lifetimes compared with the related terpyridine complexes of Ru(ii). In DMSO, complexes 1 and 2 act as sensors for F(-) and to a lesser extent for AcO(-), CN(-) and H2PO4(-), whereas 3 acts as a sensor for F(-), AcO(-), CN(-) and to some extent for H2PO4(-). In contrast to DMSO, all the complexes exhibit very high selectivity towards cyanide ions in the presence of an excess of other anions in aqueous medium. The complexes display visual detection of cyanide with the detection limit lying in the range of 1.01 × 10(-7) to 9.79 × 10(-8) M. Equilibrium constants for the interaction of the complexes with the anions were evaluated from absorption and emission titration profiles and were found to lie in six orders of magnitude. It is observed that the excited-state lifetimes of the complexes were modulated to a significant extent by the selected anions in all the three media proving the utility of such complexes to act as lifetime-based sensors for anions. The fact that all the complexes can selectively sense cyanide in the presence of other anions with their detection limits lying in the range of 10(-7) M-10(-8) M in aqueous solution is particularly important for their practical applicability. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) studies were performed to understand the nature of the ground and excited states of the complexes with detailed assignments of the orbitals involved in absorption transitions. In particular, the red-shifts of the absorption and emission bands in the presence of selective anions have been well reproduced by computations.

An imidazolyl-pyreno-imidazole conjugate as a cyanide sensor and a set-reset memorized sequential logic device.

In this work a pyrenyl-bisimidazole receptor has been synthesized and fully characterized by standard analytical tools and spectroscopic techniques including single crystal X-ray crystallography. Crystal structure analysis shows the occurrence of strong π-π and CH-π interactions among the adjacent Py-BiimzH2 units. Moreover, each NH proton on the imidazole ring is involved in strong intermolecular hydrogen bonding interactions with N atoms of the neighboring unit forming infinite chains. The absorption and both steady state and time-resolved emission properties of the compound were found to be modulated to a significant extent by selective inorganic anions and transition metal cations in solution. Theoretical calculations employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were carried out and good correlation between the experimental and the TD-DFT calculated results led to the accurate assignment of the main absorption and emission bands of the original compound as well as its anionic and metal complexes. More importantly, the compound can act as an efficient ratiometric optical chemosensor for CN(-) in H2O-DMSO (9 : 1) media. The anion sensing properties of the receptor was thoroughly investigated in both neat DMSO as well as mixed H2O-DMSO (9 : 1) media through different channels. From the response profiles in terms of absorption or emission intensity and wavelength towards inorganic ions (Cu(2+) and CN(-)), we developed a molecular system which can mimic sequential Boolean logic functions of XOR, OR, XNOR and NOR logic gates. Moreover, we were able to construct a memory device which nicely demonstrates the "Write-Read-Erase-Read" behavior.

pH-Induced processes in wire-like multichromophoric homo- and heterotrimetallic complexes of Fe(II), Ru(II), and Os(II).

In this work we studied the influence of pH on the absorption, steady state and time-resolved emission spectroscopic behaviors of recently reported multichromophoric trimetallic complexes of the forms [(bpy)2M(phen-Hbzim-tpy)M'(tpy-Hbzim-phen)M(bpy)2](6+) (M = Ru(II) or Os(II), and M' = Fe(II), Ru(II), and Os(II)) derived from a heteroditopic phenanthroline-terpyridine bridge, 2-(4-(2,6-di(pyridin-2-yl)pyridine-4-yl)phenyl)-1H-imidazole[4,5-f][1,10]phenanthroline (tpy-Hbzim-phen) and 2,2'-bipyridine (bpy) as the auxiliary ligand. For purposes of comparison, the UV-vis absorption and emission titrations of three monometallic model compounds [(bpy)2Ru(phen-Hbzim-tpy)](ClO4)2 (1), [(bpy)2Os(phen-Hbzim-tpy)] (ClO4)2 (2) and [(tpy-PhCH3)Ru(tpy-Hbzim-phen)](ClO4)2 (3), where tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine) were studied under the same experimental conditions. The absorption titration data were used to determine the ground state pKa values, whereas the luminescence and lifetime data were utilized for the determination of excited state pKa* values of the complexes. The evolving factor analyses of the set of absorption spectra of the complexes obtained by varying the pH of the solution confirm that only three absorbing species exist in the pH window of 2-12. Moreover, the modulation of the rate of the intramolecular energy transfer among the components in the homo- and heterotrimetallic complexes as a function of pH of the solution was also demonstrated.

Ruthenium(II) and osmium(II) mixed chelates based on pyrenyl-pyridylimidazole and 2,2'-bipyridine ligands as efficient DNA intercalators and anion sensors.

We report herein the synthesis and characterization of two monometallic ruthenium(II) and osmium(II) complexes of composition [(bpy)2M(HImzPPy)] (ClO4)2 derived from pyrenylimidazole-10-pyridin-2-yl-9H-9,11-diazacyclopenta[e]pyrene (HImzPPy) and 2,2'-bipyridine (bpy) ligands. X-ray crystallographic study shows that both crystals belong to the triclinic system having space group P1̅. The photophysical properties of 1 and 2 in acetonitrile indicate that the metal-to-ligand charge-transfer excited state is mainly centered in the [M(bpy)2](2+) moiety of the complexes and slightly affected by the extended conjugation of the pyrenylimidazole moiety. Both complexes display one-electron reversible metal-centered oxidative processes and a number of quasi-reversible reductive processes. The binding affinities of the complexes toward calf-thymus DNA (CT-DNA) were thoroughly studied through different methods such as absorption, emission, excited-state lifetime, circular dichroism, and thermal denaturation of DNA and a relative DNA binding study using ethidium bromide. All of these experiments account for the intercalative nature of both 1 and 2 toward CT-DNA as well as their light-switch behavior. The anion recognition study through different spectroscopic techniques reveals that both complexes act as "turn-on" luminescence sensors for H2PO4(-) and "turn-off" sensors toward F(-) and AcO(-). The imidazole N-H proton of the receptors gets deprotonated with the excessive addition of F(-) and AcO(-), while it interacts with H2PO4(-) through hydrogen-bonding interaction. Theoretical calculations (DFT and TD-DFT) were also performed to understand the photophysical properties of the metalloreceptors.

Multichromophoric bimetallic Ru(II) terpyridine complexes based on pyrenyl-bis-phenylimidazole spacer: synthesis, photophysics, spectroelectrochemistry, and TD-DFT calculations.

A symmetrical bridging ligand, 5,11-bis(4-([2,2':6',2″-terpyridine]-4'-yl)phenyl)-4,12-dihydropyreno[4,5-d:9,10-d']diimidazole (tpy-H2PhImzPy-tpy), containing terpyridyl coordinating units connected via a pyrenyl-bis-phenylimidazole spacer have been designed to synthesize a new class of light harvesting bimetallic Ru(II) complexes. The electronic properties of this complexes can be fine-tuned by varying tridentate terminal ligands. Full characterization of the compounds has been done with the help of (1)H NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis. Geometry optimization of the complexes was also carried out with density functional theory (DFT). Electronic absorption spectra exhibit a number of very intense π-π* and n-π* transitions in the UV and moderately intense MLCT and ILCT transitions in the visible region. Interestingly, the present bimetallic complexes exhibit moderately strong luminescence in the range between 657 and 703 nm and lifetimes (long component) between 5.8 and 67.0 ns at room temperature showing the dependence of the emission characteristics upon the type of terminal ligand and solvent. Detailed temperature-dependent emission measurements showed that an overall enhancement of photoluminescence intensity and lifetime occur in all three cases upon lowering of temperature. The redox behavior of the compounds is characterized by a single reversible anodic wave corresponding to two closely spaced one-electron processes. The appearance of intervalence charge transfer transition (IVCT) bands in the NIR region on electrochemical generation of Ru(II)Ru(II)/Ru(II)Ru(III) species indicates the presence of substantial electronic communication among the two ruthenium centers in the bimetallic complexes. DFT and TDDFT calculations were also done for better understanding of the absorption and emission spectral characteristics of the complexes.

Demonstration of multiple logic operations in a heteroditopic pyrene-phenylimidazole-terpyridine conjugate based on optical responses by selective anions and cations: an experimental and theoretical investigation.

Combined experimental and density functional theory (DFT) and time-dependent density functional theory (TD-DFT) studies were carried out to investigate the structural and electronic properties of a terpyridyl-phenylimidazole system covalently linked to pyrene, 10-(4-[2,2':6',2"-terpyridine]terpyridin-4'-yl-phenyl)-9H-9,11-diazacyclopenta[e]pyrene (tpy-HImzPy). X-ray crystal structure determination shows that the compound crystallized in monoclinic form with the space group P21/c. The anion and cation sensing properties of tpy-HImzPy were thoroughly studied in dimethyl sulfoxide and in mixed dimethyl sulfoxide-water medium through different channels such as absorption, steady-state and time-resolved emission, and (1)H NMR spectroscopic methods. In this work, by grafting the pyrene moiety into the terpyridyl chelating unit, an intraligand-charge-transfer sensitive chromophore has been developed whose absorption and emission behaviors are highly sensitive to selective anions and cations, and the response profiles in terms of absorption or emission intensity and wavelength toward the tested ions varied quite a lot. On the basis of these observations, we developed a unique molecular system capable of performing multiple logic functions such as INHIBIT, OR, XOR, NOR, and XNOR by simply varying the combination and level of various ionic inputs in a systematic manner. In this work, we will also be particularly interested to see the effect of selective anion and cation on the optical properties of receptor by means of computational studies and correlate them with the experimentally observed data.

Light harvesting and directional energy transfer in long-lived homo- and heterotrimetallic complexes of Fe(II), Ru(II), and Os(II).

A new family of trimetallic complexes of the form [(bpy)2 M(phen-Hbzim-tpy)M'(tpy-Hbzim-phen)M(bpy)2](6+) (M=Ru(II), Os; M'=Fe(II), Ru(II), Os; bpy=2,2'-bipyridine) derived from heteroditopic phenanthroline-terpyridine bridge 2-{4-[2,6-di(pyridin-2-yl) pyridine-4-yl]phenyl}-1H-imidazole[4,5-f][1,10]phenanthroline (phen-Hbzim-tpy) were prepared and fully characterized. Zn(2+) was used to prepare mixed-metal trimetallic complexes in situ by coordinating with the free tpy site of the monometallic precursors. The complexes show intense absorptions throughout the UV/Vis region and also exhibit luminescence at room temperature. The redox behavior of the compounds is characterized by several metal-centered reversible oxidation and ligand-centered reduction processes. Steady-state and time-resolved luminescence data show that the potentially luminescent Ru(II)- and Os(II)-based triplet metal-to-ligand charge-transfer ((3)MLCT) excited states in the triads are quantitatively quenched, most likely by intercomponent energy transfer to the lower lying (3)MLCT (for Ru and Os) or triplet metal-centered ((3)MC) excited states of the Fe(II) subunit (nonluminescent). Interestingly, iron did not adversely affect the photophysics of the respective systems. This suggests that the multicomponent molecular-wire-like complexes investigated here can behave as efficient light-harvesting antennas, because all the light absorbed by the various subunits is efficiently channeled to the subunit(s) in which the lowest-energy excited states are located.

Synthesis, structural characterization, and multichannel anion and cation sensing studies of a bifunctional Ru(II) polypyridyl-imidazole based receptor.

A mixed-ligand monometallic ruthenium(ii) complex of composition [(bipy)2Ru(tpy-Hbzim-dipy)](ClO4)2 (), where tpy-Hbzim-dipy = 4'-[4-(4,5-di-pyridin-2-yl-1H-imidazol-2-yl)-phenyl]-[2,2';6',2'']terpyridine and bipy = 2,2'-bipyridine has been synthesized and characterized using standard analytical and spectroscopic techniques including X-ray crystallography. The complex displays very intense, ligand centered absorption bands in the UV and moderately intense MLCT bands in the visible region. On excitation at the MLCT bands, the complex exhibits strong luminescence at room temperature with lifetimes in the range of 116-257 ns, depending upon the nature of the solvents. The complex is found to undergo one reversible oxidation in the positive potential window (0 to +1.8 V) and two successive quasi-reversible reductions in the negative potential window (0 to -2.0 V). Both anion and cation binding properties of the receptor were thoroughly investigated in acetonitrile solution using (1)H NMR, absorption, steady state and time-resolved emission spectral studies and by cyclic voltammetry. The anion sensing studies revealed that the receptor acts as a "turn on" luminescence sensor for H2PO4(-) and HSO4(-) ions, and as a "turn off" sensor for F(-) and AcO(-) ions. It is evident that in the presence of excess F(-) and AcO(-) ions, deprotonation of the imidazole N-H fragment of the receptor occurs, an event which is signaled by the change of color from orange yellow to red visible to the naked eye. On the other hand, the probable mode of interaction of the receptors with H2PO4(-) and HSO4(-) ions is through hydrogen bonding interaction. The cation-sensing properties showed that the receptor was found to exhibit a colorimetric sensing ability that was highly selective for Fe(2+), as evidenced by the distinct color change from yellow orange to deep red-violet to the naked eye over the other cations studied (Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+)).

A combined experimental and DFT/TD-DFT investigation of structural, electronic, and cation-induced switching of photophysical properties of bimetallic Ru(II) and Os(II) complexes derived from imidazole-4,5-dicarboxylic acid and 2,2'-bipyridine.

Experimental results coupled with computational studies were utilized to investigate the structural and electronic properties of mixed-ligand bimetallic ruthenium(II) and osmium(II) complexes of composition [(bpy)2M(Imdc)M(bpy)2](+) [M = Ru(II) (1) and M = Os(II) (2)], where H3Imdc = imidazole-4,5-dicarboxylic acid and bpy = 2,2'-bipyridine. The X-ray crystal structures of both the bimetallic complexes were determined which showed that compound 1 crystallizes in monoclinic form with space group P2(1)/c, while 2 is obtained in orthorhombic form with the space group Pca2(1). The optimized geometrical parameters for the complexes computed both in the gas phase and in solution are reported and compared with the single-crystal X-ray data. The absorption spectra, redox behaviors, and luminescence properties of the complexes were thoroughly investigated. The complexes display very intense, ligand-centered absorption bands in the UV and moderately intense MLCT bands in the visible regions. While the Ru(II) complex displays moderately strong luminescence, the corresponding Os(II) complex does not luminesce at room temperature. Both the bimetallic complexes show two successive one-electron reversible metal-centered oxidations. The effect of alkali, alkaline earth, and transition metal cations on the absorption and emission spectral behavior of the complexes has also been studied in detail. As compared to the luminescence intensities and the quantum yields of the free complexes, those of the complexes were enhanced substantially in the presence of selective cations showing cation-induced molecular switching behaviors. Density functional theory (DFT) and time-dependent DFT (TD-DFT) studies provide insight into the nature of the ground and excited states with resulting detailed assignments of the orbitals involved in absorption and emission transitions. In particular, the blue-shifts of the absorption and emission bands in the presence of cations are also reproduced by our calculations.

Photoinduced electron and energy transfer and pH-induced modulation of the photophysical properties in homo- and heterobimetallic complexes of ruthenium(II) and rhodium(III) based on a heteroditopic phenanthroline-terpyridine bridge.

Homo- and heterobimetallic complexes of compositions [(bpy)2Ru(II)(phen-Hbzim-tpy)Ru(II)(tpy/tpy-PhCH3/H2pbbzim)](4+) and [(bpy)2Ru(II)(phen-Hbzim-tpy)Rh(III)(tpy-PhCH3/H2pbbzim)](5+), where phen-Hbzim-tpy = 2-[4-(2,6-dipyridin-2-ylpyridin-4-yl)phenyl]-1H-imidazole[4,5-f][1,10]phenanthroline, bpy = 2,2'-bipyridine, tpy = 2,2':6',2"-terpyridine, tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2"-terpyridine, and H2pbbzim = 2,6-bis(benzimidazol-2-yl)pyridine, have been synthesized and characterized by elemental analyses, electrospray ionization mass spectrometry, and (1)H NMR spectroscopy. The absorption spectra, redox behavior, and luminescence properties of these bimetallic complexes have been thoroughly investigated and compared with those of monometallic [(bpy)2Ru(II)(phen-Hbzim-tpy)](2+) and [(tpy-PhCH3)Rh(III)(tpy-Hbzim-phen)](3+) model compounds. The electrochemistry of the complexes shows a reversible Ru(II/III) oxidation in the anodic region and an irreversible Rh(III/I) reduction and several ligand-based reductions in the cathodic region. Steady-state and time-resolved luminescence data at room temperature show that an efficient intramolecular electronic energy transfer from the metal-to-ligand charge-transfer (MLCT) excited state of the [(bpy)2Ru(II)(phen-Hbzim-tpy)] chromophore to the MLCT state of the tpy-containing chromophore [(phen-Hbzim-tpy)Ru(II)(tpy/tpy-PhCH3/H2pbbzim)] occurs in all three unsymmetrical homobimetallic complexes. On the other hand, for both heterometallic dyads, an efficient intramolecular photoinduced electron transfer from the excited ruthenium moiety to the rhodium-based unit takes place. The rate constants for the energy- and electron-transfer processes have been determined by time-resolved emission spectroscopy. The influence of the pH on the absorption, steady-state, and time-resolved emission properties of complexes has been thoroughly investigated. The absorption titration data were used to determine the ground-state pK values, whereas the luminescence data were utilized for determination of the excited-state acid dissociation constants. In effect, deprotonation of the azole NH moieties of the complexes leads to a substantial lowering of the MLCT absorption and emission band energies.