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Cu(I) 4H-imidazolate complexes are rare examples of Cu(I) complexes with chelating anionic ligands and are potent photosensitizers with unique absorption and photoredox properties. In this contribution, five novel heteroleptic Cu(I) complexes with monodentate triphenylphosphine co-ligands are investigated. As a consequence of the anionic 4H-imidazolate ligand and in contrast to comparable complexes with neutral ligands, these complexes are more stable than their homoleptic bis(4H-imidazolato)Cu(I) congeners. Here, the ligand exchange reactivity was studied by 31 P-, 19 F-, and variable temperature NMR and the ground state structural and electronic properties by X-ray diffraction, absorption spectroscopy, and cyclic voltammetry. The excited-state dynamics were investigated by femto- and nanosecond transient absorption spectroscopy. The observed differences, with respect to chelating bisphosphine bearing congeners, are often due to the increased geometric flexibility of the triphenylphosphines. These observations render the investigated complexes interesting candidates for photo(redox)reactions not accessible with chelating bisphosphine ligands., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

In this paper, the photophysical behavior of four panchromatically absorbing, homoleptic bis(4H-imidazolato)Cu I complexes, with a systematic variation in the electron-withdrawing properties of the imidazolate ligand, were studied by wavelength-dependent time-resolved femtosecond transient absorption spectroscopy. Excitation at 400, 480, and 630 nm populates metal-to-ligand charge transfer, intraligand charge transfer, and mixed-character singlet states. The pump wavelength-dependent transient absorption data were analyzed by a recently established 2D correlation approach. Data analysis revealed that all excitation conditions yield similar excited-state dynamics. Key to the excited-state relaxation is fast, sub-picosecond pseudo-Jahn-Teller distortion, which is accompanied by the relocalization of electron density onto a single ligand from the initially delocalized state at Franck-Condon geometry. Subsequent intersystem crossing to the triplet manifold is followed by a sub-100 ps decay to the ground state. The fast, nonradiative decay is rationalized by the low triplet-state energy as found by DFT calculations, which suggest perspective treatment at the strong coupling limit of the energy gap law., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The intense absorption of light to covering a large part of the visible spectrum is highly desirable for solar energy conversion schemes. To this end, we have developed novel anionic bis(4H-imidazolato)Cu(I) complexes (cuprates), which feature intense, panchromatic light absorption properties throughout the visible spectrum and into the NIR region with extinction coefficients up to 28,000 M -1  cm -1 . Steady-state absorption, (spectro)electrochemical and theoretical investigations reveal low energy (Vis to NIR) metal-to-ligand charge-transfer absorption bands, which are a consequence of destabilized copper-based donor states. These high-lying copper-based states are induced by the σ-donation of the chelating anionic ligands, which also feature low energy acceptor states. The optical properties are reflected in very low, copper-based oxidation potentials and three ligand-based reduction events. These electronic features reveal a new route to panchromatically absorbing Cu(I) complexes., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)