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 through thermally activated delayed fluorescence (TADF) from an interligand charge transfer (ICT) process. A series of cMa derivatives was prepared to examine the variables that 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 efficiencies (Φ PL > 0.95) and fast radiative rates (k r = 4 × 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 the increased separation between the hole and electron in the ICT excited state. Analysis of temperature-dependent luminescence data and theoretical calculations indicate that the hole−electron separation exerts a primary effect on the energy gap between the lowest-energy singlet and triplet states (ΔE ST ) while keeping the radiative rate for the singlet state relatively unchanged. This interpretation provides guidelines for the design of new cMa derivatives with even faster radiative rates in addition to those with slower radiative rates and thus extended excited state lifetimes.Article pubs.acs.org/JACS

Generating 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 that can be used as sensitizers to promote the light-driven reduction of water to hydrogen. The cMa complexes studied here absorb visible photons (εvis > 103 M–1 cm–1), maintain long excited-state lifetimes (τ ∼ 0.2–1 μs), and perform stable photoinduced 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 the two-coordinate complexes herein can perform photodriven 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 fuel photosensitizers that offer exceptional tunability and photoredox properties.

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Generating sustainable fuel from sunlight plays an important role in meeting the energy demands of the modern age. Here we report the synthesis of new two-coordinate, molecular Cu(I) and Au(I) complexes that were designed to absorb visible photons (vis > 103 M-1cm-1), maintain long excited state lifetimes (~1-0.1s), and perform stable photo-induced charge transfer to a target substrate with remarkably potent photoreducing capabilities (E+/* up to 2.33 V vs. Fc+/0). The photoredox performance was evaluated in a variety of solvents, and we were able to understand the influence of ligand design and metal center on the photophysical properties. Interestingly, we found that the Cu(I) systems have competitive figures of merit with widely used scarce metal photosensitizers such as Ru(bpy)32+ and Ir(ppy)3. This work illuminates two-coordinate coinage metal complexes as promising, abundant metal, solar fuels photosensitizers that offer exceptional tunability and photoredox properties.