Diversity of Copper(I) Complexes Showing Thermally Activated Delayed Fluorescence: Basic Photophysical Analysis

A comparison of three copper­(I) compounds [<b>1</b>, Cu­(dppb)­(pz₂Bph₂); <b>2</b>, Cu­(pop)­(pz₂Bph₂); <b>3</b>, Cu­(dmp)­(phanephos)⁺] that show pronounced thermally activated delayed fluorescence (TADF) at ambient temperature demonstrates a wide diversity of emission behavior. In this study, we focus on compound <b>1</b>. A computational density functional theory (DFT)/time-dependent DFT approach allows us to predict detailed photophysical properties, while experimental emission studies over a wide temperature range down to <i>T</i> = 1.5 K lead to better insight into the electronic structures even with respect to spin–orbit coupling efficiencies, radiative rates, and zero-field splitting of the triplet state. All three compounds, with emission quantum yields higher than ϕ_PL = 70%, are potentially well suited as emitters for organic light-emitting diodes (OLEDs) based on the singlet-harvesting mechanism. Interestingly, compound <b>1</b> is by far the most attractive one because of a very small energy separation between the lowest excited singlet S₁ and triplet T₁ state of Δ<i>E</i>(S₁–T₁) = 370 cm^–1 (46 meV). Such a small value has not been reported so far. It is responsible for the very short decay time of τ­(TADF, 300 K) = 3.3 μs. Hence, if focused on the requirements of a short TADF decay time for reduction of the saturation effects in OLEDs, copper­(I) complexes are well comparable or even slightly better than the best purely organic TADF emitters

[Copper(phenanthroline)(bisisonitrile)]⁺‑Complexes for the Visible-Light-Mediated Atom Transfer Radical Addition and Allylation Reactions

A series of heteroleptic [Cu­(phenantroline)­(bisisonitrile)]⁺-complexes was synthesized, and their structural, spectroscopic, and electrochemical properties were investigated. The new copper­(I) complexes were employed as photoredox-catalysts in the visible-light-mediated atom transfer radical addition (ATRA). Especially, [Cu­(dpp)­(binc)]­BF₄ (<b>6a-BF</b>_<b>4</b>)­(dpp = 2,9-diphenyl-1,10-phenanthroline; binc = bis­(2-isocyanophenyl) phenylphosphonate) proved to be highly active owing to an enhanced excited-state lifetime compared to the commonly employed [Cu­(dap)₂]Cl (<b>1-Cl</b>)­(dap = 2,9-di­(<i>p</i>-anisyl)-1,10-phenanthroline). Furthermore, the catalyst could be applied to allylation reactions with trimethylallylsilane under mild visible-light photoredox conditions

Synthesis, Structure, and Spectroelectrochemistry of Ferrocenyl–Meldrum’s Acid Donor–Acceptor Systems

The synthesis of two new donor–acceptor ferrocenyl derivatives with Meldrum’s acid based nonplanar acceptor substituents is presented. Both compounds are obtained in high yields in a simple reaction protocol under mild conditions using either 1-acetyl- or 1,1′-diacetylferrocene and Meldrum’s acid. Both products have been characterized spectroscopically, by single-crystal X-ray structure analysis, by electrochemical and UV/vis/IR spectroelectrochemical measurements, and by (TD)-DFT calculations. The spectroelectrochemical measurements disclose that the 2,2-dimethyl-1,3-dioxane-4,6-dione moiety is a moderately strong electron acceptor

Synthesis, Structure, and Spectroelectrochemistry of Ferrocenyl–Meldrum’s Acid Donor–Acceptor Systems

The synthesis of two new donor–acceptor ferrocenyl derivatives with Meldrum’s acid based nonplanar acceptor substituents is presented. Both compounds are obtained in high yields in a simple reaction protocol under mild conditions using either 1-acetyl- or 1,1′-diacetylferrocene and Meldrum’s acid. Both products have been characterized spectroscopically, by single-crystal X-ray structure analysis, by electrochemical and UV/vis/IR spectroelectrochemical measurements, and by (TD)-DFT calculations. The spectroelectrochemical measurements disclose that the 2,2-dimethyl-1,3-dioxane-4,6-dione moiety is a moderately strong electron acceptor

Photophysical Properties of Cyclometalated Pt(II) Complexes: Counterintuitive Blue Shift in Emission with an Expanded Ligand π System

A detailed examination was performed on photophysical properties of phosphorescent cyclometalated (C^∧N)­Pt­(O^∧O) complexes (ppy)­Pt­(dpm) (<b>1</b>), (ppy)­Pt­(acac) (<b>1</b>′), and (bzq)­Pt­(dpm) (<b>2</b>) and newly synthesized (dbq)­Pt­(dpm) (<b>3</b>) (C^∧N = 2-phenylpyridine (ppy), benzo­[<i>h</i>]­quinoline (bzq), dibenzo­[<i>f</i>,<i>h</i>]­quinoline (dbq); O^∧O = dipivolylmethanoate (dpm), acetylacetonate (acac)). Compounds <b>1</b>, <b>1</b>′, <b>2</b>, and <b>3</b> were further characterized by single crystal X-ray diffraction. Structural changes brought about by cyclometalation were determined by comparison with X-ray data from model C^∧N ligand precursors. The compounds emit from metal-perturbed, ligand-centered triplet states (<i>E</i>_0–0 = 479 nm, <b>1</b>; <i>E</i>_0–0 = 495 nm, <b>2</b>; <i>E</i>_0–0 = 470 nm, <b>3</b>) with disparate radiative rate constants (<i>k</i>_r = 1.4 × 10⁵ s^–1, <b>1</b>; <i>k</i>_r = 0.10 × 10⁵ s^–1, <b>2</b>; <i>k</i>_r = 2.6 × 10⁵ s^–1, <b>3</b>). Zero-field splittings of the triplet states (Δ<i>E</i>_III–I = 11.5 cm^–1, <b>1</b>′; Δ<i>E</i>_III–I < 2 cm^–1, <b>2</b>; Δ<i>E</i>_III–I = 46.5 cm^–1, <b>3</b>) were determined using high resolution spectra recorded in Shpol’skii matrices. The fact that the <i>E</i>_0–0 energies do not correspond to the extent of π-conjugation in the aromatic C^∧N ligand is rationalized on the basis of structural distortions that occur upon cyclometalation using data from single crystal X-ray analyses of the complexes and ligand precursors along with the triplet state properties evaluated using theoretical calculations. The wide variation in the radiative rate constants and zero-field splittings is also explained on the basis of how changes in the electronic spin density in the C^∧N ligands in the triplet state alter the spin–orbit coupling in the complexes

Photophysical Properties of Cyclometalated Pt(II) Complexes: Counterintuitive Blue Shift in Emission with an Expanded Ligand π System

A detailed examination was performed on photophysical properties of phosphorescent cyclometalated (C^∧N)­Pt­(O^∧O) complexes (ppy)­Pt­(dpm) (<b>1</b>), (ppy)­Pt­(acac) (<b>1</b>′), and (bzq)­Pt­(dpm) (<b>2</b>) and newly synthesized (dbq)­Pt­(dpm) (<b>3</b>) (C^∧N = 2-phenylpyridine (ppy), benzo­[<i>h</i>]­quinoline (bzq), dibenzo­[<i>f</i>,<i>h</i>]­quinoline (dbq); O^∧O = dipivolylmethanoate (dpm), acetylacetonate (acac)). Compounds <b>1</b>, <b>1</b>′, <b>2</b>, and <b>3</b> were further characterized by single crystal X-ray diffraction. Structural changes brought about by cyclometalation were determined by comparison with X-ray data from model C^∧N ligand precursors. The compounds emit from metal-perturbed, ligand-centered triplet states (<i>E</i>_0–0 = 479 nm, <b>1</b>; <i>E</i>_0–0 = 495 nm, <b>2</b>; <i>E</i>_0–0 = 470 nm, <b>3</b>) with disparate radiative rate constants (<i>k</i>_r = 1.4 × 10⁵ s^–1, <b>1</b>; <i>k</i>_r = 0.10 × 10⁵ s^–1, <b>2</b>; <i>k</i>_r = 2.6 × 10⁵ s^–1, <b>3</b>). Zero-field splittings of the triplet states (Δ<i>E</i>_III–I = 11.5 cm^–1, <b>1</b>′; Δ<i>E</i>_III–I < 2 cm^–1, <b>2</b>; Δ<i>E</i>_III–I = 46.5 cm^–1, <b>3</b>) were determined using high resolution spectra recorded in Shpol’skii matrices. The fact that the <i>E</i>_0–0 energies do not correspond to the extent of π-conjugation in the aromatic C^∧N ligand is rationalized on the basis of structural distortions that occur upon cyclometalation using data from single crystal X-ray analyses of the complexes and ligand precursors along with the triplet state properties evaluated using theoretical calculations. The wide variation in the radiative rate constants and zero-field splittings is also explained on the basis of how changes in the electronic spin density in the C^∧N ligands in the triplet state alter the spin–orbit coupling in the complexes