A series of four-coordinate heteroleptic copper(I) complexes with diimine and β-diketiminate ligands

Long Excited-State Lifetimes in Three-Coordinate Copper(I) Complexes via Triplet–Triplet Energy Transfer to Pyrene-Decorated Isocyanides

“…The synthetic procedure for three new heteroleptic Cu(I) complexes (Cu1−Cu3) is outlined in Scheme 1, following a procedure similar to the synthesis of four-coordinate copper(I) complexes previously presented by our group. 17 All three complexes were prepared by stirring equimolar amounts of CuO t Bu and the protonated CyNacNac Me (H) proligand for 1 h at room temperature first. Subsequently, 0.7 equiv of the respective isocyanide ligand was added and the mixture was stirred for 2−4 h at room temperature.…”

“…We investigated this strategy in a series of four-coordinate heteroleptic copper(I) complexes bearing diimine ligands and β-diketiminate (NacNac) ligands, which have superior visible absorption compared to typical copper(I) photosensitizers, dominated by low-energy charge-transfer bands that cover a wide range of the visible and even the near-IR regions. 17,18 However, even with sterically crowding alkyl substituents on one or both ligands, these chromophores only have excitedstate lifetimes of 2 ns or less. 19 Additionally, in the tetrahedral four-coordinate environment, the HOMO on the NacNac and the LUMO on the diimine are in perpendicular orientations, which results in a symmetry-forbidden HOMO → LUMO excitation, reducing the oscillator strength of the chargetransfer transition.…”

“…The most actively investigated classes of copper­(I) photosensitizers are homoleptic four-coordinate complexes with the general formula [Cu­(N^N) 2 ] + , with N^N representing a diimine ligand, and the heteroleptic [Cu­(N^N)­(P^P)] + versions pairing one diimine with one diphosphine ligand. − A common strategy for improving excited-state lifetimes in copper­(I) bis-chelate photosensitizers involves sterically crowded ligand designs, which inhibit excited-state (pseudo) Jahn–Teller distortions that lead to rapid nonradiative decay. We investigated this strategy in a series of four-coordinate heteroleptic copper­(I) complexes bearing diimine ligands and β-diketiminate (NacNac) ligands, which have superior visible absorption compared to typical copper­(I) photosensitizers, dominated by low-energy charge-transfer bands that cover a wide range of the visible and even the near-IR regions. , However, even with sterically crowding alkyl substituents on one or both ligands, these chromophores only have excited-state lifetimes of 2 ns or less . Additionally, in the tetrahedral four-coordinate environment, the HOMO on the NacNac and the LUMO on the diimine are in perpendicular orientations, which results in a symmetry-forbidden HOMO → LUMO excitation, reducing the oscillator strength of the charge-transfer transition.…”

Sterically Encumbered Aryl Isocyanides Extend Excited-State Lifetimes and Improve the Photocatalytic Performance of Three-Coordinate Copper(I) β-Diketiminate Charge-Transfer Chromophores

“…The development of effective molecular photosensitizers is crucial for various applications in energy-related fields − as well as synthetic organic chemistry. − While precious heavy transition metal-based coordination compounds featuring iridium­(III), , ruthenium­(II), , and platinum­(II) , have traditionally been favored due to their higher efficiency in photocatalysis, there is growing interest in exploring cheaper alternatives such as first-row transition metal-based coordination compounds − and metal-free organic chromophores. − Among the first-row transition metals, copper­(I) complexes have garnered significant attention due to their relatively longer metal-to-ligand charge transfer (MLCT) excited-state lifetimes, attributed to the absence of deleterious metal-centered (MC) states. The majority of copper­(I) complexes that have been studied so far are homoleptic or heteroleptic four-coordinate structures using phenanthroline derivatives or diphosphine ligands. − Another series of four-coordinate structures bearing β-diketiminate (NacNac) ligands has been prepared by our group. − The electron-rich nature of β-diketiminate ligands destabilizes the HOMO energy level, resulting in a smaller HOMO–LUMO gap and broad absorption across the visible region, which is crucial for solar harvesting. However, a series of complexes gave no photocatalytic activity, which we attribute to their short excited-state lifetimes that maximize at ∼2 ns …”