Influence of Ancillary Ligand on the Photosensitization and Photophysical Properties of Red Luminescent Tri-fluorinated Β-diketonate Eu(III) Complexes.

Highly emissive ternary Eu(III) complexes were synthesized with a tri-fluorinated ß-diketone as principal ligand and heterocyclic aromatic compounds as ancillary ligands to assess their utility as an illuminating material for display devices and other optoelectronics. The general characterizations, regarding the coordinating facets of complexes were accomplished via various spectroscopic techniques. Thermal stability was investigated via TGA/DTA. Photophysical analysis was accomplished by PL studies, Band gap value, color parameters and J-O analysis. DFT calculations were performed adopting geometrically optimized structure of complexes. Superb thermal stability has been achieved in complexes, which decides their concrete candidature for display devices. The bright red luminescence of complexes is ascribed to 5D0 → 7F2 transition of Eu(III) ion. Colorimetric parameters unlocked the applicability of complexes as warm light source and J-O parameters adequately summarized the coordinating surrounding around the metal ion. Various radiative properties were also evaluated which suggested the prospective use of complexes in lasers and other optoelectronic devices. The band gap and Urbach band tail, procured from absorption spectra, revealed the semiconducting behavior of synthesized complexes. DFT studies rendered the energies of FMO and various other molecular parameters. It can be summarized from the photophysical and optical analysis of synthesized complexes that these complexes are virtuous luminescent materials and possess potentiality to be used in diverse domain of display devices.

Exploration of Optical and Radiative Properties of Fluorinated ß-keto Carboxylate Tb3+ Complexes Emanating Cool Green Light.

Tb3+ complexes with ß-ketocarboxylic acid as main ligand and heterocyclic systems as auxiliary ligand were synthesized and analyzed to assess their prospective relevance as green light emitting material. The complexes were characterized via various spectroscopic techniques and were found to be stable up to ≈ 200 ℃. Photoluminescent (PL) investigation was performed to assess the emissive nature of complexes. Longest luminescence time of decay (1.34 ms) and highest intrinsic quantum efficiency (63.05%) were fetched for complex T5. Color purity of complexes was found to be in range 97.1 - 99.8% which demonstrated the aptness of these complexes in green color display devices. NIR Absorption spectra were employed to evaluate Judd-Ofelt parameters to appraise the luminous performance and environment encircling Tb3+ ions. The JO parameters were found to follow the order: Ω2 > Ω4 > Ω6 and suggested the higher covalence character in complexes. Theoretical branching ratio in the range 65.32 - 72.68%, large stimulated emission cross section and narrow FWHM for 5D4 → 7F5 transition unlocked the relevance of these complexes as a green color laser media. Band gap and Urbach analysis were consummated via enforcing nonlinear curve fit function on absorption data. Two band gaps with values in between 2.02 - 2.93 eV established the prospective use of complexes in photovoltaic devices. Energies of HOMO and LUMO were estimated employing geometrically optimized structures of complexes. Investigation of biological properties accomplished via antioxidant and antimicrobial assays which communicated their applicability in biomedical domain.

Study of Judd-Ofelt, Urbach energy and photosensitization process in luminescent Sm(III) complexes with heterocyclic ligands.

Six samarium (III) complexes were synthesised by employing the ß-ketocarboxylic acid as main ligand and five N-donor systems as ancillary ligands through the environmentally safe liquid-assisted grinding method. Various characterisation techniques were employed to determine the structure of the complexes i.e. NMR, IR, XRD and SEM. Photoluminescent studies were carried out in solid as well as in solution form. In solid and solution form emission spectra show maximum intensity peak at 604 and 602 nm, respectively, assigned to 4G5/2 → 6H7/2 transition which explains orange emission on UV excitation in complexes. CCT, CP, colorimetric parameters and quantum yield (relative and intrinsic) of the synthesized complexes were calculated. With the help of reflectance spectra, band gap and Urbach energy were determined. Lasing parameters were also calculated by employing FWHM values obtained from Gaussian fitting. Energy transfer study revealed the efficacious energy transfer from ligand to metal's emissive level. Further antimicrobial studies revealed higher activity in case of complexes in comparison to ligand.

Computational analysis, Urbach energy and Judd-Ofelt parameter of warm Sm3+ complexes having applications in photovoltaic and display devices.

In this work, six reddish orange Sm3+ complexes were synthesized using organic ligand (L) and secondary ligands having hetero atoms by a one-step significant liquid-assisted grinding method and were characterized by spectroscopic techniques. The Urbach energy and band gap energy of the complexes were inspected by a linear fit. Using a least square fitting method, the Judd-Ofelt parameter and radiative properties were also determined. Thermal analysis, colorimetric analysis, luminescence decay time and anti-microbial properties of complexes were studied. The luminescence emission spectra of binary and ternary complexes displayed three characteristic peaks at 565, 603 and 650 nm in the powder form and four peaks at 563, 605, 646 and 703 nm in a solution phase due to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 transitions respectively. The most intense transition in the solid phase (4G5/2 → 6H7/2) is accountable for orange color, and in the solution form, the highly luminescent peak (4G5/2 → 6H9/2) is responsible for reddish orange color of Sm3+ complexes. PXRD and SEM analyses suggested that the complexes possess a nanoparticle grain size with crystalline nature. The decent optoelectrical properties of title complexes in the orangish-red visible domain indicated possible applications in the manufacturing of display and optoelectronic devices.

Photophysical, optical and lasing analysis of fluorinatedß-keto carboxylate europium(III) complexes.

Six luminescent, bright red Eu(III) complexes with aß-keto-carboxylic acid as prime ligand and N-donor aromatic systems as auxillary ligand were synthesised via ecologically efficient grinding method. The distinctive red peak (5D0 â†’ 7F2) of Eu(III) ion is exhibited in emission spectra of all complexes. The luminescent properties of complexes were analysed through decay time, color coordinates, luminescence efficiency and Judd Ofelt parameters. The value of Ω2is found to be higher than Ω4which indicated hypersensitive nature of5D0 â†’ 7F2transition. The results established the complexes as a strong contender for red light emitting display devices. The fluorescence branching ratios, stimulated emission cross section, gain band width and optical gain showed the good lasing strength of5D0 â†’ 7F2transition of complexes. The complexes exhibited decent thermal stability and have optical energy band gap value in semiconductor range, thus can have relevance in optoelectronic devices. Energy transfer mechanism was investigated for complexes which affirmed the efficacious transfer of energy from ligands to Eu(III) ion. The synthesised complexes were also assayed for antimicrobial and antioxidant properties. All complexes are reported to show better antioxidant behaviour than the prime ligand and also exhibited upstanding antibacterial activities.

Augmentation of photophysical features and Judd-Ofelt analysis of extensively green glowing terbium (III) complexes with nitrogen donor ancillary ligands.

Six green glowing terbium (III) complexes were fabricated via grinding method utilizing a prime organic ligand (L) and nitrogen donor ancillary ligands. Characterization of synthesized complexes was accomplished through various spectroscopic techniques. The significant thermal stability was determined by thermogravimetric analysis while the energy bandgap and Urbach energy were investigated through diffused reflectance spectra of these complexes. The peak observed at 548 nm in emission spectra is responsible for the virescent color of these complexes. Color purity, decay time, quantum yield, and emission intensities of ternary complexes were significantly improved as compared to binary ones due to the synergistic effect of ancillary ligands. Judd-Ofelt parameters were determined by the NIR absorption spectrum, which claims the asymmetric environment around the terbium (III) ion. CCT values advocate the applicability of these complexes in green light-emitting materials as a cool light source. The biological assignments reveal the significance of these complexes as potent antioxidants and antimicrobial agents. The energy transfer process highlights the enhancement of luminescence in these complexes via the synergic effect of ligands. Our investigation portrays that these complexes can be employed in laser technology, display devices, semiconductors, biological fields, and optoelectronic devices.

Applicability of Reddish-Orange Light Emitting Samarium (III) Complexes for Biomedical and Multifunctional Optoelectronic Devices.

Six crimson samarium (III) complexes based on ß-ketone carboxylic acid and ancillary ligands were synthesized by adopting the grinding technique. All synthesized complexes were investigated via elemental analysis, infrared, UV-Vis, NMR, TG/DTG and photoluminescence studies. Optical properties of these photostimulated samarium (III) complexes exhibit reddish-orange luminescence due to 4G5/2 → 6H7/2 electronic transition at 606 nm of samarium (III) ions. Further, energy bandgap, color purity, CIE color coordinates, CCT and quantum yield of all complexes were determined accurately. Replacement of water molecules by ancillary ligands enriched these complexes (S2-S6) with decay time, quantum yield, luminescence, energy bandgap and biological properties than parent complex (S1). Interestingly, these efficient properties of complexes may find their applications in optoelectronics and lighting systems. In addition to these, the antioxidant and antimicrobial assays were also investigated to explore the applications in biological assays.

The Sesamum indicum Rhizosphere Associated Bacterium: A Source of Antifungal Compound.

BACKGROUND: The impact of fungal infections on human health has increased considerably within a past few decades. Although drugs with antifungal properties are available, but they are less effective and are associated with side effects. OBJECTIVE AND METHOD: To screen the bacterial isolates from Sesamum indicum and to investigate the antifungal activity of the screened bacterial isolates against Aspergillus sp. Co-culture assay and agar overlay were used to scrutinize the anti-Aspergillus activity. Furthermore, optimization of media and growth conditions to enhance the production of anti-Aspergillus compound. RESULTS: Several bacterial cultures were isolated from Sesamum indicum rhizosphere collected from Mandi (H.P.) India. These bacterial cultures were assayed for antifungal activity against Aspergillus species i.e. A. fumigatus and A. niger. Two most potent strains were chosen for more detailed analyses. The biochemical characterization and 16S ribosomal RNA sequencing revealed that Burkholderia sp. strain RC1 and Acinetobacter pittii strain RC2 exhibit strong similarity (100%) with Burkholderia sp. SR2-07 and Acinetobacter sp. strain 3-59. Additionally, it was also validated that RC1 and RC2 showed significant difference in the production of anti-Aspergillusactivity under altered growth conditions. CONCLUSION: Results from this study recommend that plant rhizosphere remains a rich hotspot for delivering a novel antifungal compounds.

Coumarin Derivatives as Adjuvants: From In Silico Physicochemical Characterization to In Vitro Evaluation against Gram Positive Bacteria.

AIMS: A series of acylated coumarin derivatives have been evaluated for their in silico ADMET properties and in vitro antibacterial activities. METHODS AND RESULTS: In silico analysis confirmed their physicochemical properties in conformation with various layout filters and further their ADMET properties were predicted. Antibacterial activities were evaluated by Resazurin based microbroth dilution assay against standard Gram positive bacteria: Staphylococcus aureus (MTCC No. 3160) and Bacillus cereus (MTCC No. 10085). When used alone, these derivatives showed higher MIC values. However, in combination with standard drugs they exhibited synergistic effects according to fractional inhibitory concentration index. The synergistic effect was further confirmed by time kill curves. Their cytotoxity was evaluated by haemolytic assay and they were found to be non-toxic upto a concentrations of 500 µg ml-1. CONCLUSION: The data support the potential use of acylated coumarin derivatives as next generation adjuvants as evaluated by their in silico ADMET analysis and in vitro antibacterial and cytotoxicity evaluation. Further research involving these combinations is warranted. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests that acylated coumarin derivatives act as antibacterial adjuvants in combination with standard drugs and have potential to be used in pharmaceutical preparations.

Perspectives on Phytochemicals as Antibacterial Agents: An Outstanding Contribution to Modern Therapeutics.

Despite the considerable advancements in the development of antimicrobial agents, incidents of epidemics due to multi drug resistance in microorganisms have created a massive hazard to mankind. Due to increased resistance against conventional antibiotics, researchers and pharmaceutical industries are more concerned about novel therapeutic agents for the prevention of bacterial infections. Enormous wealth of traditional system of medicine gains importance in health therapies over again. With ancient credentials of potent medicinal plants, various herbal remedies came forward for the management of bacterial infections. The Ayurvedic approach facilitates the development of new therapeutic agents due to structural and functional diversity among phytochemicals. The abundance and diversity is responsible for the characterization of new lead structures from medicinal plants. Industrial interest has increased due to recent research advancements viz. synergistic and high-throughput screening approach for the evaluation of vast variety of phytochemicals. The review certainly emphasizes on the traditional medicines as alternatives to conventional chemotherapeutic drugs. The review briefly describes mode of action of various antibiotics and resistance mechanisms. This review focuses on the chemical diversity and various mechanisms of action of phytochemicals against bacterial pathogens.

Combination therapy: the propitious rationale for drug development.

Therapeutic options for many infections are extremely limited and at crisis point. We run the risk of entering a second pre-antibiotic era. There had been no miracle drug for the patients infected by resistant microbial pathogens. Most of the very few new drugs under development have problems with their toxicity, or pharmacokinetics and pharmacodynamics. We are already decades behind in the discovery, characterization and development of new antimicrobials. In that scenario, we could not imagine surviving without newer and effective antimicrobial agents. Bacteria have been the champions of evolution and are still evolving continuously, where they pose serious challenges for humans. Along with the crisis of evolving resistance, the condition is made worst by the meager drug pipeline for new antimicrobials. Despite ongoing efforts only 2 new antibiotics (Telavancin in 2009 and Ceftaroline fosamil in 2010) have been approved since 2009 pipeline status report of Infectious Disease Society of America (IDSA). Recent approval of new combination based antiviral drugs such as Stribild (combination of four drugs for HIV treatment) and Menhibrix (combination vaccine to prevent meningococcal disease and Haemophilus influenzae type b in children) proves that combination therapy is still the most promising approach to combat the ever evolving pathogens. Combination therapy involves the drug repurposing and regrouping of the existing antimicrobial agents to provide a synergistic approach for management of infectious diseases. This review article is an effort to highlight the challenges in new drug development and potential of combination drug therapy to deal with them.