scholarly journals Synthesis, characterization and photophysical studies of cyclometalated Au(III) complexes

2015 ◽  
Author(s):  
◽  
Lakshmi Nilakantan
Keyword(s):  
Emission Spectrum ◽  
Room Temperature ◽  
Stokes Shift ◽  
Energy Difference ◽  
Single Step ◽  
Reductive Coupling ◽  
Tin Compounds ◽  
Synthetic Strategy ◽  
Dithiocarbamate Ligand ◽  
Phosphorescence At Room Temperature

We report here a series of room temperature emissive biphenyl cyclometalated gold (III) diethyl dithiocarbamate complexes (DEDT) having H, CF3, OMe and tBu substitutions on the biphenyl moiety. Synthesis of these complexes was accomplished by a single step reaction of the appropriate dilithiobiphenyl reagent with Au(DEDT)Cl2. The Au(DEDT)Cl2 complex played an important role in the success of our reaction, where the chelating sulfur ligand stabilizes the Au(III) center and keeps it intact without reducing to Au(I) or colloidal gold during the course of its reaction with the lithium compound. In comparison with other literature reported procedures for analogous Au(III) complexes, this methodology gave better yields with lesser number of reaction steps as well as without using toxic chemicals such as sodium cyanide or tin compounds. All of these complexes exhibit phosphorescence at room temperature as well as in low temperature glasses. While substitution on the biphenyl moiety by electron donating OMe and tBu groups red shifted the emission band when compared with hydrogen counterparts, the electron withdrawing CF3 groups made no difference. The emission from these complexes is mainly governed by the metal perturbed 3??* transitions of biphenyl and this assignment is well supported by the observed photo physical properties such as vibronic structured emission, lifetime in microseconds, large stokes shift, solvent independent emission spectrum as well as the oxygen quenching of the emission spectrum. Further DFT studies on these complexes also showed that the transition from LUMO+2 to HOMO. (3pi-pi*) is responsible for the emission. This is in contrast with lowest energy absorption which is mainly from HOMO-L+1 (LLCT). This is rationalized by the existence of a relaxed 3pi-pi* (-3.31 eV) state in lower energy when compared with the relaxed 3LLCT state (-1.61 eV) as well as the large energy difference between singlet and triplet pi-pi* states. We also hereby report the synthesis of a bis(diethyldithiocarbamate(DEDT) -S,S)-(naphthyl-1,8) digold(II) complex with a formal Au-Au bond. Our synthetic strategy involved reductive coupling via lithiation of dibromonaphthalene precursor followed by reaction with Au(DEDT)Cl2. This digold complex is unique when compared with known digold(II) complexes, which are traditionally synthesized by oxidative addition of halogen to digold(I) complexes. The digold complex has been characterized by NMR, XRD, UV-Vis and elemental analysis. DFT reasoned the UV-Vis absorption of complex 3 at 379 nm to the transition from sigmaAu-Au) orbital into sigma*(Au-Au) orbital with some contributions from the dithiocarbamate ligand (LMCT). However this complex shows no emission at 298 or 77 K. The lack of emission could possibly be due to low-lying non-emissive d-d states.

Generation of Phosphoranyl Radicals via Photoredox Catalysis Enables Voltage–Independent Activation of Strong C–O Bonds

2018 ◽  
Author(s):  
Erin Stache ◽  
Alyssa B. Ertel ◽  
Tomislav Rovis ◽  
Abigail G. Doyle
Keyword(s):  
Carboxylic Acids ◽  
Functional Groups ◽  
Single Step ◽  
Direct Access ◽  
Photoredox Catalysis ◽  
Acyl Radical ◽  
Synthetic Strategy ◽  
Acyl Radicals ◽  
Benzyl Radicals ◽  
Aliphatic Carboxylic Acids

Alcohols and carboxylic acids are ubiquitous functional groups found in organic molecules that could serve as radical precursors, but C–O bonds remain difficult to activate. We report a synthetic strategy for direct access to both alkyl and acyl radicals from these ubiquitous functional groups via photoredox catalysis. This method exploits the unique reactivity of phosphoranyl radicals, generated from a polar/SET crossover between a phosphine radical cation and an oxygen centered nucleophile. We first show the desired reactivity in the reduction of benzylic alcohols to the corresponding benzyl radicals with terminal H-atom trapping to afford the deoxygenated product. Using the same method, we demonstrate access to synthetically versatile acyl radicals which enables the reduction of aromatic and aliphatic carboxylic acids to the corresponding aldehydes with exceptional chemoselectivity. This protocol also transforms carboxylic acids to heterocycles and cyclic ketones via intramolecular acyl radical cyclizations to forge new C–O, C–N and C–C bonds in a single step.

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

New Potential Biologically Active Compounds: Synthesis and Characterization of Urea and Thiourea Derivativpes Bearing 1,2,4-oxadiazole Ring

2020 ◽  
Vol 17 (7) ◽  
pp. 525-534 ◽  
Author(s):  
Nevin Arıkan Ölmez ◽  
Faryal Waseer
Keyword(s):  
Microwave Irradiation ◽  
Room Temperature ◽  
Antimicrobial Activities ◽  
Phenyl Isocyanate ◽  
Single Step ◽  
Biologically Active Compounds ◽  
Biologically Active ◽  
Active Compounds ◽  
Thiourea Derivatives ◽  
Acyl Chlorides

Background: Urea, thiourea, and 1,2,4-oxadiazole compounds are of great interest due to their different activities such as anti-inflammatory, antiviral, analgesic, fungicidal, herbicidal, diuretic, antihelminthic and antitumor along with antimicrobial activities. Objective: In this work, we provide a new series of potential biologically active compounds containing both 1,2,4-oxadiazole and urea/thiouprea moiety. Materials and Methods: Firstly, 5-chloromethyl-3-aryl-1,2,4-oxadiazoles (3a-j) were synthesized from the reaction of different substituted amidoximes (2a-j) and chloroacetyl chloride in the presence of pyridine by conventional and microwave-assisted methods. In the conventional method, 1,2,4-oxadiazoles were obtained in two steps. O-acylamidoximes obtained in the first step at room temperature were heated in toluene for an average of one hour to obtain 1,2,4-oxadiazoles. The yields varied from 70 to 96 %. 1,2,4-oxadiazoles were obtained under microwave irradiation in a single step in a 90-98 % yield at 160 °C in five minutes. 5-aminomethyl-3-aryl-1,2,4- oxadiazoles (5a-j) were obtained by Gabriel amine synthesis in two steps from corresponding 5-chloromethyl-3- aryl-1,2,4-oxadiazoles. Finally, twenty new urea (6a-j) and thiourea (7a-j) compounds bearing oxadiazole ring were synthesized by reacting 5-aminomethyl-3-aryl-1,2,4-oxadiazoles with phenyl isocyanate and isothiocyanate in tetrahydrofuran (THF) at room temperature with average yields (40-70%). Results and Discussions: An efficient and rapid method for the synthesis of 1,2,4-oxadiazoles from the reaction of amidoximes and acyl halides without using any coupling reagent under microwave irradiation has been developed, and twenty new urea/thiourea compounds bearing 1,2,4-oxadiazole ring have been synthesized and characterized. Conclusion: We have synthesized a new series of urea/thiourea derivatives bearing 1,2,4-oxadiazole ring. Also facile synthesis of 3,5-disubstituted 1,2,4-oxadiazoles from amidoximes and acyl chlorides under microwave irradiation was reported. The compounds were characterized using FTIR, 1H NMR, 13C NMR, and elemental analysis techniques.

Crystal Structures of and Polarized Absorption-Spectroscopy in Racemic and Resolved [Ru(bpy)3] (ClO4)2 and [Zn(bpy)3] (ClO4)2Bpy=2,2'-Bipyridine

1995 ◽  
Vol 48 (5) ◽  
pp. 929 ◽  
Author(s):  
E Krausz ◽  
H Riesen ◽  
AD Rae
Keyword(s):  
Room Temperature ◽  
Energy Difference ◽  
Temperature Structure ◽  
Asymmetric Unit ◽  
Threefold Axis ◽  
Crystal Forms ◽  
The Third ◽  
Racemic Form ◽  
Ligand Charge Transfer ◽  
Dominant Influence

[Zn( bpy )3] (ClO4)2 and [ Ru ( bpy )3] (ClO4)2 are isomorphous in both their racemic and resolved crystal forms. The resolved materials are monohydrates and have a C 2, Z = 8, structure with two independent formula units on general sites in the asymmetric unit. The cations have the same chirality. The inherent threefold axis of each cation lies approximately parallel to the c axis. The unrelated racemic form has a C2/c, Z = 4, structure which is a commensurate modulation of a P3c1, Z = 2, parent structure, typified by the room-temperature structure of [ Ru ( bpy )3] (PF6)2. A primary, secondary and tertiary axis of P3c1 become the c, b and a axes respectively of C2/c, retaining a third of the symmetry elements of P3c1. The crystals grow as multiply contacted twins. This structure bas just one spectroscopic site with the cation lying on a twofold axis that passes through the metal and one of the bidendate ligands and relates the other two ligands to each other. This feature is particularly useful in the study of the optical spectroscopy of the metal-to- ligand charge transfer excitations of [ Ru ( bpy )3]2+ and related systems. A comparison of structural and spectral data indicates that the positions of the anions have a dominant influence on the relative energies of the metal-to- ligand excitations. An energy difference between excitations involving the two (lower-energy) equivalent ligands and the third ligand of the order of 800 cm-1 is indicated in both singlet and triplet regions for the racemic perchlorate. The absorption spectra of [ Ru ( bpy )3]2+and [Os( bpy )3]2+ in a number of crystalline hosts are compared and discussed.

scholarly journals Green Chemical Synthesis of N-Cholyl-L-Cysteine Encapsulated Gold Nanoclusters For Fluorometric Detection of Mercury Ions

2021 ◽  
Author(s):  
Kasthuri Jayapalan ◽  
Sivasamy Arumugam ◽  
Rajendiran Nagappan
Keyword(s):  
Uv Light ◽  
Stokes Shift ◽  
Gold Nanoclusters ◽  
Green Emission ◽  
Fluorescence Analysis ◽  
Cost Effective ◽  
Single Step ◽  
Fluorometric Detection ◽  
Transmission Electron ◽  
Green Chemical Synthesis

Abstract Here we report a simple, single-step, cost-effective, environmentally friendly, and biocompatible approach using sodium salt of N-cholyl-L-cysteine (NaCysC) capped gold nanoclusters (AuNCs) with green emission properties at above the CMC in aqueous medium under UV-light irradiation. The primary and secondary CMC of NaCysC was found to be 4.6 and 10.7 mM respectively using pyrene as fluorescent probe. The synthesized AuNCs exhibit strong emission maxima at 520 nm upon excitation of 375 nm with a large Stokes shift of 145 nm. The surface functionality and morphology of NCs are studied by Fourier transform infrared spectroscopy, dymanic light scattering studies and transmission electron microscopy. The formation of AuNCs was completed within 5 h and exhibit high stability for more than 6 months. The NaCysC templated AuNCs selectively quenches the Hg2+ ions with higher sensitivity in aqueous solution over the other metal ions. The fluorescence analysis of Hg2+ showed a wide linear range from 15 to 120 µM and a detection limit was found to be 15 nM.

scholarly journals Spectral Properties of Hybrid of Rhodamine (6G) Dyes Doped Epoxy Resin Dissolved in Chloroform

2019 ◽  
Vol 16 (3(Suppl.)) ◽  
pp. 0764 ◽  
Author(s):  
Al-Hamdani Et al.
Keyword(s):  
Epoxy Resin ◽  
Quantum Efficiency ◽  
Fluorescence Spectra ◽  
Room Temperature ◽  
Rhodamine 6G ◽  
Energy Gap ◽  
Radiative Lifetime ◽  
Stokes Shift ◽  
Fluorescence Emission ◽  
Absorption And Fluorescence Spectra

            The research is dealing with the absorption and fluorescence spectra for the hybrid of  an Epoxy Resin doped with organic dye Rhodamine (R6G) of different concentrations (5*10-6, 5*10-5, 1*10-5, 1*10-4, 5*10-4) Mol/ℓ at room temperature. The Quantum efficiency Qfm, the rate of fluorescence emission Kfm (s-1), the non-radiative lifetime τfm (s), fluorescence lifetime τf and the Stokes shift were calculated. Also the energy gap (Eg) for each dye concentration was evaluated. The results showed that the maximum quantum efficiency 62 % and maximum stokes shift 96 nm was obtained in dye concentration 5*10-6 and 1*10-4. The energy gap ranges between 1.066 eV to 1.128 eV depending proportionally on the dye concentrations.

The effect of imidazole on the enhancement of gadolinium-porphyrin phosphorescence at room temperature

2016 ◽  
Vol 45 (42) ◽  
pp. 16889-16895 ◽  
Author(s):  
Lixin Zang ◽  
Huimin Zhao ◽  
Jianyu Hua ◽  
Feng Qin ◽  
Yangdong Zheng ◽  
...  
Keyword(s):  
Room Temperature ◽  
Phosphorescence At Room Temperature

The mechanism for the 40-fold enhancement in Gd-HMME RTP intensity by adding imidazole and Gd3+ is revealed.

Preliminary Study of WO3 Nanostructures Produced via Facile Hydrothermal Synthesis Process for CO2 Sensing

2013 ◽  
Vol 431 ◽  
pp. 37-41 ◽  
Author(s):  
Amirul Abd Rashid ◽  
Nor Hayati Saad ◽  
Chia Sheng Daniel Bien ◽  
Wai Yee Lee ◽  
M.A.S.M. Haniff
Keyword(s):  
Room Temperature ◽  
Gas Sensing ◽  
Hydrothermal Reaction ◽  
Hydrothermal Process ◽  
Single Step ◽  
Synthesis Process ◽  
Sensor Element ◽  
Response Measurement ◽  
Sensor Fabrication ◽  
Preliminary Study

Tungsten trioxide (WO3) nanostructure with aspect ratio of 20 (length/diameter) have been successfully synthesized by single step hydrothermal reaction at moderate temperature of 180 °C. The crystal structure and morphology evolution are characterized by SEM and Raman while the carbon dioxide (CO2) sensing capability was tested by simple sensor fabrication .It was observed that the nanorods were initially coalesce in bundles before breaking up loosely towards the end of the hydrothermal process. A response measurement reveals that the sensor was able to detect CO2 at room temperature with the sensitivity around 13ohm/100 ppm. The detection performance of such nanostructure provides a positive indication that it can be a competitive sensor element candidate not only for CO2 applications in particular but can be expanded to other gas sensing application such as O2, C2H4 and NO2.

Alternative technology concepts for low-cost and high-speed 2D and 3D interconnect manufacturing

2013 ◽  
Vol 2013 (1) ◽  
pp. 000001-000006
Author(s):  
F. Roozeboom ◽  
M. Smets ◽  
B. Kniknie ◽  
M. Hoppenbrouwers ◽  
G. Dingemans ◽  
...  
Keyword(s):  
High Speed ◽  
Room Temperature ◽  
Microelectromechanical Systems ◽  
Low Cost ◽  
Industrial Process ◽  
Atomic Layer ◽  
Single Step ◽  
Thermal Mode ◽  
Different Types ◽  
Sidewall Passivation

The current industrial process of choice for Deep Reactive Ion Etching (DRIE) of 3D features, e.g. Through-Silicon Vias (TSVs), Microelectromechanical Systems (MEMS), etc., is the Bosch process, which uses alternative SF6 etch cycles and C4F8-based sidewall passivation cycles in a time-sequenced mode. An alternative, potentially faster and more accurate process is to have wafers pass under spatially-divided reaction zones, which are individually separated by so-called N2-gas bearings ‘curtains’ of heights down to 10–20 μm. In addition, the feature sidewalls can be protected by replacing the C4F8-based sidewall passivation cycles by cycles forming chemisorbed and highly uniform passivation layers of Al2O3 or SiO2 deposited by Atomic Layer Deposition (ALD), also in a spatially-divided mode. ALD is performed either in thermal mode, or plasma-assisted mode in order to achieve near room-temperature processing. For metal filling of 3D-etched TSVs, or for deposition of 2D metal conductor lines one can use Laser-Induced Forward Transfer (LIFT) of metals. LIFT is a maskless, ‘solvent’-free deposition method, utilizing different types of pulsed lasers to deposit thin material (e.g. Cu, Au, Al, Cr) layers with μm-range resolution from a transparent carrier (ribbon) onto a close-by acceptor substrate. It is a dry, single-step, room temperature process in air, suitable for different types of interconnect fabrication, e.g. TSV filling and redistribution layers (RDL), without the use of wet chemistry.

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