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  1. A series of bimetallic carbene-metal-amide (cMa) complexes have been prepared with bridging biscarbene ligands to serve as a model for the design of luminescent materials with large oscillator strengths and small energy differences between the singlet and triplet states (dE ST). The complexes have a general structure (R2N)Au(:carbene—carbene:)Au(NR2). The bimetallic complexes show solvation-dependent absorption and emission that is analyzed in detail. It is found that the molar absorptivity of the bimetallic complexes is correlated with the energy barrier to rotation of the metal-ligand bond. The bimetallic cMa complexes also exhibit short emission lifetimes (t = 200-300 ns) with high photoluminescence efficiencies (PL >95%). The radiative rates of bimetallic cMa complexes are 3 to 4 times faster than that of the corresponding monometallic complexes. Analysis of temperature-dependent luminescence data indicates that the lifetime for the singlet state (τ_(S_1 )) of bimetallic cMa complexes are near 12 ns with a dE ST of 40 50 meV. The presented compounds provide a general design for cMa complexes to achieve small values for dE ST while retaining high radiative rates. Solution processed OLEDs made using two of the complexes as luminescent dopants show high efficiency and low roll-off at high luminance. 
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    Free, publicly-accessible full text available September 13, 2024
  2. Temperature dependent luminescence studies were performed on one-dimensional organic–inorganic lead halide hybrid materials to obtain activation energies for non-radiative decay.

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    Free, publicly-accessible full text available August 23, 2024
  3. This study presents the synthesis and characterization of two spirobifluorenyl derivatives substituted with either triphenylmethyl (SB-C) or triphenylsilyl (SB-Si) moieties for use as host materials in phosphorescent organic light-emitting diodes (PHOLED). Both molecules have similar high triplet energies and large energy gaps. Blue Ir(tpz)3 and green Ir(ppy)3 phosphorescent devices were fabricated using these materials as hosts. Surprisingly, SB-Si demonstrated superior charge-transporting ability compared to SB-C, despite having similar energies for their valence orbitals. In particular, SB-Si proved to be a highly effective host for both blue and green devices, resulting in maximum efficiencies of 12.6% for the Ir(tpz)3 device and 9.6% for the Ir(ppy)3 device. These results highlight the benefits of appending the triphenylsilyl moiety onto host materials and underscore the importance of considering the morphology of hosts in the design of efficient PHOLEDs.

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    Free, publicly-accessible full text available July 1, 2024
  4. Generating a sustainable fuel from sunlight plays an important role in meeting the energy demands of the modern age. Herein we report two-coordinate carbene-metal-amide (cMa, M = Cu(I) and Au(I)) complexes can be used as sensitizers to promote the light driven reduction of water to hydrogen. The cMa complexes studied here absorb visible photons (vis > 103 M-1cm-1), maintain long excited state lifetimes (~ 0.2-1 s) and perform stable photo-induced charge transfer to a target substrate with high photoreducing potential (E+/* up to 2.33 V vs. Fc+/0 based on a Rehm-Weller analysis). We pair these coinage metal complexes with a cobalt-glyoxime electrocatalyst to photocatalytically generate hydrogen and compare the performance of the copper- and gold-based cMa complexes. We also find that these two-coordinate complexes presented can perform photo-driven hydrogen production from water without the addition of the cobalt-glyoxime electrocatalyst. In this “catalyst free” system the cMa sensitizer partially decomposes to give metal nanoparticles that catalyze water reduction. This work identifies two-coordinate coinage metal complexes as promising abundant metal, solar fuels photosensitizers that offer exceptional tunability and photoredox properties. 
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    Free, publicly-accessible full text available June 28, 2024
  5. Two-coordinate carbene-MI-amide (cMa, MI = Cu, Ag, Au) complexes have emerged as highly efficient luminescent materials for use in a variety of photonic applications, due to their extremely fast radiative rates via thermally activated delayed fluorescence (TADF) from an interligand charge transfer (ICT) process. A series of cMa derivatives were prepared to examine the variables which affect the radiative rate with the goal of understanding the parameters that control the radiative TADF process in these materials. We find that blue emissive complexes with high photoluminescence efficiency (PL > 0.95) and fast radiative rates (kr = 4 x 106 s-1) can be achieved by selectively extending the -system of the carbene and amide ligands. Of note is the role played by increasing the separation between the hole and electron in the ICT excited state. Analysis of temperature dependent luminescence data along with theoretical calculations indicate that the hole-electron separation alters the energy gap between the lowest energy singlet and triplet states (dE ST) while keeping the radiative rate for the singlet state unchanged. This interpretation provides guidelines for the design of new cMa derivatives with even faster radiative rates as well as those with slower radiative rates and thus extended excited state lifetimes. 
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  6. A series of twelve two-coordinate coinage metal, Cu, Ag and Au, complexes with carbene-metal-amide structures were prepared. The complexes all display thermal assisted delayed fluorescence (TADF) emission at room temperature from interligand charge transfer (ICT) excited state with short lifetimes (less than 2 μs) and photoluminescent quantum yields that reach near unity. Owing to the involvement of the substituents in the emissive transitions and different metal ion volume, the natural transition orbital (NTO) overlap of the emissive state can be adjusted in a wide range from 0.21 to 0.41. Investigations on the relationship between the NTO overlap of the emissive state and key TADF photophysical properties demonstrated that both singlet–triplet energy gap and radiative decay rate of S 1 state increase along with the NTO overlap exponentially. Consequently, the overall TADF radiative decay rate leads to a maximum when plotted against the NTO overlap, giving the ideal zone from 0.25 to 0.30 for high TADF radiative decay rate in this class of two-coordinate coinage metal complex luminophores. 
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  7. The dynamic photoluminescence properties, and potential quenching mechanisms, ofanti-B18H22, 4,4′-Br2-anti-B18H20, and 4,4′-I2-anti-B18H20are investigated in solution and polymer films.

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