Coinage metal complexes for near infrared emission and energy transfer photocatalysis

Abstract

Herein I present comprehensive studies on synthesis, structure, and photophysical behavior of a series of luminescent CuI phosphide (-PPh2) complexes supported by various mono- and bidentate phosphines displaying TADF behaviour. Depending upon the stoichiometry used two heteroleptic dimers and four heteroleptic polynuclear CuI clusters could be isolated from the self-assembly reaction of CuI-phosphide and phosphine ligand. These complexes are green-to-red (1-2 & 4-6) and NIR (3) photo-emitters with emission maxima varying over the range λmax = 515 to 890 nm. Moderate to high photoluminescence quantum yield (Ф = 20-44% ), with a relatively high radiative rate constant of up to 3 × 10^6 s^-1, and short lifetimes τ = 0.1-34 μs were observed. Compounds 2 and 5 exhibit pronounced thermochromism and evidence of dual TADF behaviour originating from two different types of excited states. I also report a new sterically demanding, electrophilic [2.2]isoindolinophanyl-based carbene (iPC) that bears a [2.2]paracyclophane moiety. The iPC ligand is a very potent π-chromophore, which participates in low energy IL-“through-space”-CT transitions in [Au(iPC)2]OTf (8) in the visible. The steric demand of the iPC leads to a high stability of 8 against air, moisture, or solvent attack, and ultralong-lived green phosphorescence with a lifetime of 185 μs is observed in solution. The beneficial photophysical and electronic properties of the iPC ligand, including a large accessible π surface area, were exploited by employing highly efficient energy transfer (EnT) photocatalysis in a [2+2] styrene cycloaddition reaction using 8, which outperformed other established photocatalysts in comparison. In addition I also describe a series of linear copper(I) carbene carbazolate complexes (9-12) bearing the [2.2]isoindolino-phanyl-based carbene (iPC) ligand as a potent excited state π-acceptor. The compounds show efficient TADF from ligand-to-ligand charge transfer (1/3LLCT) states with quantum yields of up to 0.8 and exceptional kr of 0.8-1.9×10^6 s^-1 that are among the fastest for CuI emitters, outcompeting traditional triplet emitters based on Ir^III and Pt^II.