Organic LEDs promise highly efficient lighting and display technologies. We introduce a new class of linear donor-bridge-acceptor light-emitting molecules, which enable solution-processed LEDs with near-100% internal quantum efficiency at high brightness. Key to this performance is their rapid and efficient utilization of triplet states. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs within 350 ns at ambient temperature, after reverse intersystem crossing to singlets. We find that molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, such that rapid interconversion is possible. Calculations indicate that exchange energy is tuned by relative rotation of donor and acceptor moieties about the bridge. Unlike other low exchange energy systems, substantial oscillator strength is sustained at the singlet-triplet degeneracy point

We have performed a comprehensive theoretical investigation of the structural principles of semiconducting clathrate frameworks composed of the Group 14 elements carbon, silicon, germanium, and tin. We have investigated the basic clathrate frameworks, together with their polytypes, intergrowth clathrate frameworks, and extended frameworks based on larger icosahedral building blocks. Quantum chemical calculations with the PBE0 hybrid density functional method provided a clear overview of the structural trends and electronic properties among the various clathrate frameworks. In agreement with previous experimental and theoretical studies, the clathrate II framework proved to be the energetically most favorable, but novel hexagonal polytypes of clathrate II also proved to be energetically very favorable. In the case of silicon, several of the studied clathrate frameworks possess direct and wide band gaps. The band structure diagrams and simulated powder X-ray patterns of the studied frameworks are provided and systematic preliminary evaluation of guest-occupied frameworks is conducted to shed light on the characteristics of novel, experimentally feasible clathrate compositions.

Conformationally flexible “Carbene–Metal–Amide” (CMA) complexes of copper and gold show photoemissions across the visible spectrum, including mechanochromic behavior which led to the first CMA-based white light-emitting OLED.

The composition of methylalumoxane (MAO) and its interaction with trimethylaluminum (TMA) have been investigated by a combination of chemical, spectroscopic, neutron scattering, and computational methods. The interactions of MAO with donor molecules such as THF, pyridine, and PPh 3 as a means of quantifying the content of "free" and "bound" TMA have been evaluated, as well as the ability of MAO to produce [Me 2 AlL 2 ] + cations, a measure of the electrophilic component likely to be involved in the activation of single-site catalysts. THF, pyridine, and diphenylphosphinopropane (dppp) give the corresponding TMA−donor ligand complexes accompanied by the formation of [Me 2 AlL 2 ] + cations. The results suggest that MAO contains not only Lewis acid sites but also structures capable of acting as sources of [AlMe 2 ] + cations. Another unique, but still unresolved, structural aspect of MAO is the nature of "bound" and "free" TMA. The addition of the donors OPPh 3 , PMe 3 , and PCy 3 leads to the precipitation of polymeric MAO and shows that about one-fourth of the total TMA content is bound to the MAO polymers. This conclusion was independently confirmed by pulsed field gradient spin echo (PFG-SE) NMR measurements, which show fast and slow diffusion processes resulting from free and MAO-bound TMA, respectively. The hydrodynamic radius R h of polymeric MAO in toluene solutions was found to be 12 ± 0.3 Å, leading to an estimate for the average size of MAO polymers of about 50−60 Al atoms. Small-angle neutron scattering (SANS) resulted in the radius R S = 12.0 ± 0.3 Å for the MAO polymer, in excellent agreement with PFG-SE NMR experiments, a molecular weight of 1800 ± 100, and about 30 Al atoms per MAO polymer. The MAO structures capable of releasing [AlMe 2 ] + on reaction with a base were studied by quantum chemical calculations on the MAO models (OAlMe) n (TMA) m for up to n = 8 and m = 5. Both −O−AlMe 2 −O− and −O−AlMe 2 −μ-Me− four-membered rings are about equally likely to lead to dissociation of [AlMe 2 ] + cations. The resulting MAO anions rearrange, with structures containing separated Al 2 O 2 4-rings being particularly favorable. The results support the notion that catalyst activation by MAO can occur by both Lewis acidic cluster sites and [AlMe 2 ] + cation formation.

Table of Contents EntryCopper and gold complexes stabilized by cyclic (alkyl)(amino)carbene ligands ( R L)MX, where X = halide, pseudo-halide, amide or aryloxide represent a large class of photoluminescent materials, with emission lifetimes ranging from nanosecond to microsecond regimes.

on mononuclear silver. [7] Indeed, OLED devices based on 2nd row metals in general are remarkably rare and characterized by low efficiency. [8] Here, we report silver complexes with sub-microsecond radiative triplet lifetimes and high performance in both solution and vacuum-deposited OLED devices.Complexes 1 and 2 were readily obtained from ( Ad L)AgCl [3] and carbazole/NaO t Bu as off-white (1) or yellow (2) solids (Figure 1). The compounds are stable for long periods of time both in air and in solution in nonprotic organic solvents. Unlike many silver complexes, they are not sensitive to ambient light. Thermogravimetric analysis gives decomposition temperatures (5% weight loss) of 264.8 (1) and 263.6 °C (2). The observation of the 13 C(carbene) NMR signal (δ C 263) as two sharp 13 C 109 Ag and 13 C 107 Ag coupled doublets (J AgC = 219 and 189 Hz, respectively) confirmed that the complexes do not undergo carbene ligand exchange. [9] Single crystal X-ray diffraction of 1 and 2 confirmed the mononuclear two-coordinate geometry and the absence of significant intermolecular contacts. The C1(CAAC)···N2(Cz) distance is of prime importance since it is directly related to the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) overlap, which impacts on the radiative rate and exchange energy of (carbene)metal amides; this distance is slightly longer for 1 (4.152 Å) than for 2 (4.125 Å).Both 1 and 2 show a quasi-reversible one-electron metalcentered reduction process (tetrahydrofuran (THF) solution, [ n Bu 4 N]PF 6 as supporting electrolyte; Figures S2 and S3 and Table S1, Supporting Information). The estimated LUMO energies (1: −2.86 eV; 2: −2.83 eV) compare well with those for the Au (−2.79 eV) and Cu analogs (−2.66 eV) [5] and are only marginally affected by the nature of the metal. The peak-to-peak separation ΔE p is smaller for 2 (124 mV) than for 1 (185 mV), indicating higher stability of the reduced species of 2, potentially making it a more robust emitter under electrical excitation. The HOMO levels based on the onset of the first oxidation potentials are at −5.51 and −5.29 eV for 1 and 2, respectively. These values guide the identification of host materials for OLED fabrication. [10] The electronic structure of 1 and 2 has been evaluated using density-functional theory (DFT) for the ground state and timedependent DFT (TD-DFT) [11] calculations for the excited states using the MN15 functional by Truhlar and co-workers [12] in combination with def2-TZVP basis set by Ahlrichs and Carbene metal amides are a new class of highly efficient light-emitting molecules based on a linear donor-metal-acceptor geometry. Here the synthesis, structure, and photo-and electroluminescence of carbene silver carbazolato complexes, ( Ad L)Ag(Cz) [ Ad L = adamantyl-substituted cyclic (alkyl)(amino) carbene; Cz = carbazolate (1) and 3,6-t Bu 2 Cz (2)], are reported. They display green emission with photoluminescence quantum yields of up to 74%. Efficient mixing of triplet and singlet excited states is o...

Quantum chemical calculations demonstrate the spherical aromaticity and high thermodynamic stability of Au(72), a predicted I-symmetric golden fullerene.

Electrospray-ionization mass spectrometric studies of poly(methylaluminoxane) (MAO) in the presence of [Cp2 ZrMe2 ], [Cp2 ZrMe(Cl)], and [Cp2 ZrCl2 ] in fluorobenzene (PhF) solution are reported. The results demonstrate that alkylation and ionization are separate events that occur at competitive rates in a polar solvent. Furthermore, there are significant differences in ion-pair speciation that result from the use of metallocene dichloride complexes in comparison to alkylated precursors at otherwise identical Al/Zr ratios. Finally, the counter anions that form are dependent on the choice of precursor and Al/Zr ratio; halogenated aluminoxane anions [(MeAlO)x (Me3 Al)y-z (Me2 AlCl)z Me](-) (z=1, 2, 3…︁) are observed using metal chloride complexes and under some conditions may predominate over their non-halogenated precursors [(MeAlO)x (Me3 Al)y Me](-) . Specifically, this halogenation process appears selective for the anions that form in comparison to the neutral components of MAO. Only at very high Al/Zr ratios is the same "native" anion distribution observed when using [Cp2 ZrCl2 ] when compared with [Cp2 ZrMe2 ]. Together, the results suggest that the need for a large excess of MAO when using metallocene dichloride complexes is a reflection of competitive alkylation vs. ionization, the persistence of unreactive, homodinuclear ion pairs in the case of [Cp2 ZrCl2 ], as well as a change in ion pairing resulting from modification of the anions formed at lower Al/Zr ratios. Models for neutral precursors and anions are examined computationally.