Deuterated dimethyl sulfoxide as a good NMR solvent for the characterization of alkali metal cyclopentadienides, amides, alkoxides and phenoxides

Potassium Hexamethyldisilazide (KHMDS): Solvent-Dependent Solution Structures

Solution structures of potassium hexamethyldisilazide [KHMDS] and labeled [15N]KHMDS were examined using a number of analytical methods including 29Si NMR spectroscopy and density functional theory computations. A combination of 15N-29Si couplings, 29Si chemical shifts, and the method of continuous variations reveals dimers, monomers, and ion pairs. Weakly coordinating monofunctional ligands such as toluene, N,N-dimethylethylamine, and Et3N afford exclusively dimers. 1,3-Dioxolane, THF, dimethoxyethane, hexamethylphosphoramide, and diglyme provide dimers at low ligand concentrations and monomers at high ligand concentrations. N,N,N',N'-Tetramethylethylenediamine and N,N,N',N'-tetramethylcyclohexanediamine provide exclusively dimers at all ligand concentrations at ambient temperatures and significant monomer at -80 °C. Studies of 12-crown-4 ran into technical problems. Equimolar 15-crown-5 forms a dimer, whereas excess 15-crown-5 affords a putative ion pair. Whereas equimolar 18-crown-6 also affords a dimer, an excess provides a monomer rather than a solvent-separated ion pair. [2.2.2]cryptand affords what is believed to be a contact-ion-paired cryptate. Solvation was probed using largely density functional theory (DFT) computations. Thermally corrected energies are consistent with lower aggregates and higher solvates at low temperatures, but the magnitudes of the computed temperature dependencies were substantially larger than the experimentally derived data.

Novel planar and star-shaped molecules: synthesis, electrochemical and photophysical properties

Three novel planar and star-shaped molecules containing thiophene-functionalized group and acetylenic spacers, 4-((5″-iodo-[2,2':5',2″-terthiophen]-5-yl)ethynyl)aniline (I3TEA), 4,4'-([2,2':5',2″-terthiophene]-5,5″-diylbis(ethyne-2,1-diyl))dianiline (3TDDA), 1,3,5-tris((5-((trimethylsilyl)ethynyl)thiophen-2-yl)ethynyl)benzene (TETEB) were synthesized through Sonogashira coupling reaction. Their photophysical and electrochemical properties were explored by UV-vis, photoluminescence (PL) emission and DFT calculation. Three compounds possess unusual phenomena of PL, with the concentration of gradually decreased, the intensity of PL firstly increased and then decreased, this may be due to the aggregate-enhanced emission (AEE) effect and aggregation-caused quenching (ACQ) effect. Their spectroscopic data demonstrate that D-π-A-π-D structured organic dye 3TDDA based on NH2 as donor units and 3T as acceptor units with acetylenic spacers π-conjugated chain between them exhibits good luminescent properties. Dye I3TEA with donor(D)-acceptor(A) structure shows good charge transfer because of amino functional group and iodine atom. Octupolar organic π-conjugated star-shaped molecule TETEB possesses excellent luminescent properties because of its unique structure applied in the optoelectronic field. The redox curves and results of DFT calculations suggest that three compounds have low ionization potential and low Eoxd. All the good properties demonstrate three compounds could be promising candidates for photovoltaic materials.