Understanding the Influence of Interfacial Chemistry in Core, Core/Shell and Core/Shell/Shell Quantum Dots on their Fluorescence Properties

Colloidal semiconductor nanocrystals (quantum dots) have received a great deal of attention due to their superior size tunable properties and promising applications in many areas. Some of the most practical areas of their applications include light emitting diodes (LED), photovoltaic and biological studies. Synthetic methods of these crystals is becoming more established with new strategies being reported every now and then. However, quantitative studies connecting the processes at the interface, namely core-ligand, core-shell and shell-shells, to the overall quantum dots fluorescence properties are not well understood. Specifically for cores, relating surface-atoms interactions, solvents, ligands nature, density and functional groups on quantum yields have not been exhaustively carried out. Furthermore, for the core/shell counterparts, the connection between the qualities of the starting core on its resulting core/shell quality have been left trivial without experimental back up. Here, we summarize the reports of experiments that have systematically investigated these effects on the properties of quantum dots. Combining systematic synthetic approach with characterization tools such as FTIR, X-ray photoelectron and diffraction together with time resolved visible spectroscopies, we observed that the density, nature and the orientation of the ligand functional groups play significant roles in determining the charge carrier dynamics that results on the various quantum yields and quality of the quantum dots. The experimental results also contradicted the trivial belief that starting with a high quality core material should result into high quality core/shell quantum dots. We further extended these studies by controlling both lattice mismatch and exciton confinement potential to design small, biologically friendly and highly stable core/shell/shell material. Blinking studies confirmed an interplay of both lattice strain and exciton confinement as the major factors responsible for the blinking dynamics of these core/shell/shell quantum dots. Therefore, by controlling these parameters, we were able to observe reduced blinking quantum dots with relatively moderate shell thickness. These observations will provide a useful insight while designing these particles and enhance their future applications

Bis(dicyclo­hexyl­phenyl­phosphine)iodido­silver(I) pyridine monosolvate

The structure of the title compound, [AgI(C18H27P)2]·C5H5N, shows a trigonal-planar coordinated AgI atom within a distorted IAgP2 donor set. The pyridine solvent mol­ecule is only associated with the complex via very weak inter­molecular C—H⋯N inter­actions

Dichlorido{N-[2-(diphenyl­phosphan­yl)benzyl­idene]isopropyl­amine-κ2 N,P}palladium(II) dimethyl sulfoxide monosolvate

In the title PdII complex, [PdCl2(C22H22NP)]·(CH3)2SO, the PdII atom is coordinated in an NPCl2 coordination sphere by the N(imino) and P(phosphane) atoms of the ligand and by two Cl− ions in a slightly distorted square-planar geometry [r.m.s. deviation = 0.081 (3) Å, plane defined by the four atoms around the Pd atom]. The dimethyl sulfoxide solvent mol­ecules form centrosymmetric dimers due to an inter­molecular C—H⋯O inter­action. The crystal structure is further stabilized through two inter­molecular C—H⋯π inter­actions

The influence of weak interactions on phase transformations and polymorphism in distributed n-aryl -formamides and -thioamides

A series of arylformamides and arylthioamides has been synthesized and analyzed using nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), powder and single crystal X-ray diffraction. The work involved the study of hydrogen bonding, weak intermolecular interactions, phase changes and co-crystallization in aryl - formamides and -thioamides resulting in the structure determination of twenty four crystals. Three sets of isomorphic compounds were identified from the 24 solid state structures: set one; 2,6-difluorophenylformamide (1a), 2,6- dichlorophenylformamide (2a) and 2-chloro-6-methylphenylformamide (4a); set two; 2,6-dimethylphenylthioamide (17) and 2-chloro-6- methylphenylthioamide (18) and set three; 2,6-diisopropylphenylformamide (6) and 2,6-diisopropylphenylthioamide (20). In the first two sets, 1a, 2a and 4a, and 17 and 18, there are similar regions of halogen interactions and hydrocarbon interactions with disorder in the chloro-methyl substituents in structures 4a and 18. As for compounds 6 and 20, both the chemical and geometrical effects (size and volume of the isopropyl substituents) play a role in their isomorphism. A mixture of 2,6-dichlorophenylformamide (2a) and 2,6- dimethylphenylformamide (3) yielded a co-crystal 22 in which there was one molecule in the asymmetric unit, same as co-crystal 23 [derived from 2,6- dichlorophenylthioamide (17) and 2,6-dimethylphenylthioamide (18)]. The molecules of the two co-crystals displayed disorder in the substituents on the 2 and 6 positions of the aryl ring as a result of the occurrence of chlorine and methyl groups in the same crystallographic sites. Co-crystal 22 adopted the structure of 2,6-dichlorophenylformamide 2a. Co-crystal 23 also had a ii structure similar to that of 2a and co-crystal 22. Co-crystal 24 derived from a mixture of 2,6-diisopropylphenylformamide (6) and 2,6-diisopropylphenylthioamide (20), and also had one molecule in the asymmetric unit which showed disorder in the position occupied by oxygen and sulfur atoms. The 24 structures studied exhibited a variety of motifs formed from weak intermolecular interactions. Investigation of these weak intermolecular interactions revealed four different categories1 for the arylformamides and only one category for the arylthioamides. The categories were different in their formation of N-H…O/S hydrogen bonds (in which adjacent molecules are related by 21-screw axes, glide planes or by translation) forming chains (as in category 1, 2 and 5), sheets (as in Category 3) or dimers and tetramers (as in category 4). The chains in categories 1, 2 and 5 are in the for form of spirals (molecules along the chain are related by 21-screw axes or glide planes) or stacks (molecules along the chains are related by translation). Compounds from the different categories had certain interactions that contributed most to the stabilizations of their crystals. Apart from the N-H…O/ S hydrogen bonds, π…π, C-H…π, C-F…π, C-H…F, C-H…Cl, C-H…O, Cl…Cl, Br…Br, Cl…O and Br…O interactions also had a role to play in the stabilization of the different structures. Lattice energies and the energies relating to different molecular arrangements were calculated using Gavezzottis’ OPIX program suit. This showed that the N-H…O/S hydrogen bonds and π…π interactions were the most important interactions amongst the 24 structures discussed in this work. The crystal structures, thermal behaviour and phase transformations of all arylformamides and arylthioamides have shown that a phase transformation was only observed when a halogen atom was one of the substituents and only for some of the formamides. 2,6-dichlorophenylformamide 2a and 2-chloro-6-methylphenylformamide 4a transform to a hightemperature form at 155 and 106 °C, respectively. The high-temperature forms 2b and 4b (grown by sublimation) are both monoclinic but not isomorphous, with one short axis of about 4.3 A°, and consist of chains of N– H…O hydrogen-bonded molecules stacked along the short axis, related by translation. 1a and 1b are related to the above polymorphs in their formation of N-H…O hydrogen bonding patterns. Finally, this contribution has analyzed the role of weak interactions on the structural and thermal properties of the compounds studied. In addition, a mechanism for the phase change in 2,6-dichlorophenylformamide has been proposed and rationalized through the examination of the structures themselves together with lattice energy calculations. (1. Category = different types of hydrogen bonding patterns formed by disubstituted phenyl -formamides and -thioamides discussed in this thesis)

[Bis(pyridin-2-ylmethyl) ether]- trichloridorhodium(III) dichloromethane monosolvate : unusual hydrolysis of the methylene bridge in (pyrazolylmethyl)- pyridine

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Synthesis, Physical and Antimicrobial Studies of Ferrocenyl-N-(pyridinylmethylene)anilines and Ferrocenyl-N-(pyridinylmethyl)anilines

Ferrocenyl-N-(pyridinylmethylene)anilines Schiff bases were synthesized by reaction of 3- or 4-ferrocenylaniline with either 2-, 3-, or 4-pyridinecarboxaldehyde under solvent-free conditions via mechanochemistry technique. Products were obtained in excellent yields within 10 min of grinding. The reactions afforded a melt orgummysemi-solid that solidified to the desired Schiff bases within a short time. These Schiff bases were reduced to their corresponding amines, ferrocenyl-N-(pyridinylmethyl)anilines, with NaBH4 over neutral Al2O3 solid support via grinding. Amines were obtained in excellent yields after intermittent grinding for approximately 1 h. Herein, five novel ferrocenyl-N-(pyridinylmethylene)anilines (compounds 3, 4, 6–8) and six ferrocenyl-N-(pyridinylmethyl)anilines (compounds 9–14) are reported. Compounds were characterized through FT-IR, 1H-NMR, 13C-NMR,HRMSand SC-XRDtechniques. These compounds show visible solvatochromism, whenUV-Vis absorption was measured in polar and nonpolar solvents. In changing solvent from polar to non-polar, the Schiff bases exhibited a blue shift while the amines portrayed a red shift. Electrochemical studies on these compounds reveal that redox behaviour of the iron centre is influenced by the position imine or amine groups. Antimicrobial properties of these compounds were studied for Escherichia coli, Staphylococcus aureus, Salmonella typhimirium and Candida albicans. Highest activity was recorded against Gram-positive bacteria and fungi.KEYWORDS Ferrocenyl-N-(pyridinylmethylene)anilines, ferrocenyl-N-(pyridinylmethyl)anilines, mechanochemistry technique, solventfree synthesis, antimicrobial activity

1-(Ferrocen-1-ylmeth­yl)-3-methyl­imidazol-3-ium hexa­fluorido­phosphate

The crystal structure of the title compound, [Fe(C5H5)(C10H12N2)]PF6, consists of a ferrocene-1-methyl-(3-methyl­imidazolium) cation and a hexa­fluorido­phosphate anion. The ferrocenyl rings are skewed by 6.7 (4)° from the ideal eclipsed conformation. The inter­planar angle between the plane of the substituted cyclo­penta­dienyl ring and that of the imidazole ring is 89.9 (4)°. The crystal packing is stabilized by C—H⋯F hydrogen bonds

Triethyl­ammonium hexa-μ2-acetato-κ12 O:O′-diacetato-κ2 O-aqua-μ3-oxido-triferrate(III) toluene monosolvate

The title compound, (C6H16N)[Fe3(CH3CO2)8O(H2O)]·C7H8, was serendipitously crystallized from a reaction of disilanol with iron(II) acetate. The trinuclear acetatoferrate(III) anion has a triethyl­ammonium cation as the counterion. The three Fe atoms lie on the vertices of a regular triangle and are octa­hedrally coordinated. The complete coordination of the anion includes shared ligands among the three metal ions: a central tribridging O atom and six bidentate bridging acetyl groups. The six-coordinations of two of the metal ions are completed by a monodentate acetate ligand, whereas that of the third metal ion is completed by a water mol­ecule. The uncoordinated triethyl­ammonium cation is involved in N—H⋯O hydrogen bonding to a singly coordinated acetyl group. The coordinated aqua mol­ecule is involved in bifurcated O—H⋯O hydrogen bonding. C—H⋯O inter­actions are also observed. The toluene solvent molecule is disordered over two sets of sites in a 0.609 (11):0.391 (11) ratio

trans-Carbonylchloridobis[tris(4-chlorophenyl) phosphane]rhodium(I) acetone monosolvate

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2,6-Bis(tosyl­oxymeth­yl)pyridine

The title compound, C21H21NO6S2, is organized around a twofold axis parallel to the crystallographic c axis and containing the N atom and a C atom of the pyridine ring. The tosyl moiety and the pyridine ring are both essentially planar [maximum deviations 0.028 (2) and 0.020 (3) Å, respectively]; their mean planes form a dihedral angle of 33.0 (2)°