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  1. Abstract Photoredox catalysis has proven to be a powerful tool in synthetic organic chemistry. The rational design of photosensitizers with improved photocatalytic performance constitutes a major advancement in photoredox organic transformations. This review summarizes the fundamental ground-state and excited-state photophysical and electrochemical attributes of molecular photosensitizers, which are important determinants of their photocatalytic reactivity.
    Free, publicly-accessible full text available January 1, 2023
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  4. In this Perspective, we highlight many examples of photoluminescent metal complexes supported by isocyanides, with an emphasis on recent developments including several from our own group. Work in this field has shown that the isocyanide can play important structural roles, both as a terminal ligand and as a bridging ligand for polynuclear structures, and can influence the excited-state character and excited-state dynamics. In addition, there are many examples of isocyanide-supported complexes where the isocyanide serves as a chromophoric ligand, meaning the low-energy excited states that are important in the photochemistry are partially or completely localized on the isocyanide. Finally, anmore »emerging trend in the design of luminescent compounds is to use the isocyanide as an electrophilic precursor, converted to an acyclic carbene by nucleophilic addition which imparts certain photophysical advantages. This Perspective aims to show the diverse roles played by isocyanides in the design of luminescent compounds, showcasing the recent developments that have led to a substantial growth in fundamental knowledge, function, and applications related to photoluminescence.« less
    Free, publicly-accessible full text available December 14, 2022
  5. A series of bis-cyclometalated iridium complexes were prepared which combine triazole or NHC-based cyclometalating ligands with substituted β-diketiminate (NacNac) ancillary ligands. The HOMO is localized on the NacNac ligand and its energy and associated redox potential are determined by the NacNac substitution pattern. The effect of the cyclometalating ligand, relative to the more common 2-phenylpyridine derivatives, is to destabilize the LUMO and increase the triplet excited-state energy ( E T1 ). These results are supported by DFT calculations, which show HOMOs and LUMOs that are respectively localized on the NacNac and cyclometalating ligands. With this new design, we observe moremore »negative excited-state reduction potentials, E (Ir IV /*Ir III ), with two members of the series standing out as the most potent visible-light iridium photoreductants ever reported. Stern–Volmer quenching experiments with ketone acceptors (benzophenone and acetophenone) show that the increased thermodynamic driving force for photoinduced electron-transfer correlates with faster rates relative to fac -Ir(ppy) 3 and previous generations of NacNac-supported iridium complexes. A small selection of photoredox transformations is shown, demonstrating that these new photoreductants are capable of activating challenging organohalide substrates, albeit with modest conversion.« less
  6. The design of molecular phosphors with near-unity photoluminescence quantum yields in the low-energy regions of the spectrum, red to near-infrared, is a long-standing challenge. Because of the energy gap law and the quantum mechanical dependence of radiative decay rate on the excited-state energy, compounds which luminesce in this region of the spectrum typically suffer from low quantum yields. In this article, we highlight our group's advances in the design of top-performing cyclometalated iridium complexes which phosphoresce in red to near-infrared regions. The compounds we have introduced in this body of work have the general formula Ir(C^N) 2 (L^X), where C^Nmore »is a cyclometalating ligand that controls the photoluminescence color and L^X is a monoanionic chelating ancillary ligand. The Ir(C^N) 2 (L^X) structure type is among the most widely studied and technologically successful classes of molecular phosphors, particularly when L^X = acetylacetonate (acac). In our work we have pioneered the use of electron-rich, nitrogen containing ancillary (L^X) ligands as a means of controlling the excited-state dynamics and optimizing them to give record-breaking phosphorescence quantum yields. This paper progresses through our work in three distinct regions of the spectrum – red, deep-red, and near-infrared – and summarizes the many insights we have gained on the relationships between molecular structure, frontier orbital energies, and excited-state dynamics.« less
  7. Photoredox catalysis has emerged as a powerful strategy in synthetic organic chemistry, but substrates that are difficult to reduce either require complex reaction conditions or are not amenable at all to photoredox transformations. In this work, we show that strong bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands enable high-yielding photoredox transformations of challenging substrates with very simple reaction conditions that require only a single sacrificial reagent. Using blue or green visible-light activation we demonstrate a variety of reactions, which include hydrodehalogenation, cyclization, intramolecular radical addition, and prenylation via radical-mediated pathways, with optimized conditions that only require the photocatalystmore »and a sacrificial reductant/hydrogen atom donor. Many of these reactions involve organobromide and organochloride substrates which in the past have had limited utility in photoredox catalysis. This work paves the way for the continued expansion of the substrate scope in photoredox catalysis.« less
  8. Five new near-infrared (NIR) phosphorescent bis-cyclometalated iridium( iii ) complexes, partnering highly conjugated cyclometalating ligands with quinoline-derived ancillary ligands, have been developed. These complexes have peak NIR luminescence wavelengths from 711 to 729 nm, with photoluminescence quantum yields ranging from 0.042 to 0.36.