Engineering topics

Schaab, Jonas

Publications and source records attributed to Schaab, Jonas.

3 records

DOE OSTI2023

Luminescent Bimetallic Two-Coordinate Gold(I) Complexes Utilizing Janus Carbenes

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 (ΔE ST ). The complexes have a general structure (R 2 N)Au(:carbene—carbene:)Au(NR 2 ). 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 (τ = 200–300 ns) with high photoluminescence efficiencies (Φ PL > 95%). The radiative rates of bimetallic cMa complexes are 3–4 times faster than that of the corresponding monometallic complexes. Analysis of temperature-dependent luminescence data indicates that the lifetime for the singlet state (τS 1 ) of bimetallic cMa complexes is near 12 ns with a ΔE ST of 40–50 meV. Here the presented compounds provide a general design for cMa complexes to achieve small values for ΔE ST while retaining high radiative rates. Solution-processed organic light-emitting devices (OLEDs) made using two of the complexes as luminescent dopants show high efficiency and low roll-off at high luminance.

14 SOLAR ENERGY↗

DOE OSTI2023

Two-Coordinate Coinage Metal Complexes as Solar Photosensitizers

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 (ε vis > 10 3 M -1 cm -1 ), maintain long excited state lifetimes (τ ~ 0.2-1 μs) and perform stable photo-induced charge transfer to a target substrate with high photoreducing potential (E +/* up to 2.33 V vs. Fc +/o 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. Furthermore, this work identifies two-coordinate coinage metal complexes as promising abundant metal, solar fuels photosensitizers that offer exceptional tunability and photoredox properties.

14 SOLAR ENERGY↗

DOE OSTI2022

π-Extended Ligands in Two-Coordinate Coinage Metal Complexes

Two-coordinate carbene-M I -amide (cMa, M I = 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 (Φ PL > 0.95) and fast radiative rates (k r = 4 x 10 6 s -1 ) can be achieved by selectively extending the π-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 (ΔE ST ) while keeping the radiative rate for the singlet state unchanged. As a result, 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.

14 SOLAR ENERGY↗