Intramolecular Ferromagnetic Radical–Cu^II Coupling in a Cu^II Complex Ligated with Pyridyl-Substituted Triarylmethyl Radicals

Novel metal complexes M­(hfac)₂(PyBTM)₂ [M = Cu^II, Zn^II; hfac = hexafluoroacetylacetonato; PyBTM = (3,5-dichloro-4-pyridyl)­bis­(2,4,6-trichlorophenyl)­methyl radical] were prepared. Both hexacoordinated complexes had elongated octahedral geometry, in which two PyBTM molecules coordinated at the equatorial positions in Cu^II(hfac)₂(PyBTM)₂ but at the axial positions in Zn^II(hfac)₂(PyBTM)₂. Magnetic studies revealed an intramolecular ferromagnetic exchange interaction between the spins on PyBTM and Cu^II (<i>J</i>_Cu–R/<i>k</i>_B = 47 K) based on the orthogonality of the two spin orbitals

Structures and Optical Properties of Tris(trimethylsilyl)silylated Oligothiophene Derivatives

The structures and optical properties of tris­(trimethylsilyl)­silylated oligothiophenes were examined by spectroscopies, theoretical calculations, and single-crystal X-ray measurements. Bathochromic shift from the original oligothiophenes was observed in the tris­(trimethylsilyl)­silylated ones, confirming the σ–π conjugation between Si–Si σ bonds and π-orbital. 5,5′-Bis­(tris­(trimethylsilyl)­silyl)-2,2′-bithiophene (<b>Si-T</b>_<b>2</b>) showed the highest fluorescence quantum yield (Φ_F) both in solution (0.67, excited at 350 nm) and the solid state (0.74, excited at 371 nm). The introduction of tris­(trimethylsilyl)­silyl groups led to the small nonradiative rate constant of <b>Si-T</b>_<b>2</b>, resulting in the high Φ_F in the solution state. <b>Si-T</b>_<b>2</b> also exhibited effective σ–π conjugation and poor molecular interaction, which reflected its high Φ_F in the solid state. On the contrary, lower Φ_F (0.13, excited at 331 nm) in the solid state was observed in the longest oligothiophene examined, 5,5‴-bis­(1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)­trisilan-2-yl)-2,2′:5′,2″:5″,2‴-quaterthiophene (<b>Si-T</b>_<b>4</b>). Single-crystal X-ray measurement clarified that this compound adopted a zigzag packing structure and a rare <i>syn-anti-syn</i> conformation, which led to the poor σ–π conjugation and the decrease of π-orbital overlap in the solid state

Regulation of the Rate of Dinucleation of a Monocopper(I) Complex Containing Bipyrimidine Rotary Units by Restricted Double Pyrimidine Rotation

New copper­(I) complexes with coordinated 2-(4′-methyl)­pyrimidinyl moieties were fabricated, and the isomerism of their pyrimidine ring linkage was investigated. The ligands bis­[2-(diphenylphosphino)­phenyl] ether (DPEPhos) and 4,4′-dimethyl-2,2′-bipyrimidine (dmbpm) were used to synthesize a heteroleptic copper­(I) complex, [Cu^I(DPEPhos)­(dmbpm)]·BF₄ (<b>1</b>·BF₄), and a dinuclear copper­(I) complex, [(Cu^I)₂(DPEPhos)₂(μ-dmbmp)]­(BF₄)₂ [<b>2</b>·(BF₄)₂]. The X-ray crystallographic structures, UV–vis absorption spectra, and luminescence properties of the complexes were analyzed. The thermodynamic and kinetic aspects of the isomerism of <b>1</b>·BF₄ were examined by variable-temperature NMR. Double pyrimidine ring rotation was found to be restricted sterically by the bulky DPEPhos ligands. This limited the number of the possible isomers: <b>1</b>·BF₄ showed only isomers with either one (<i>io</i> isomer) or both (<i>oo</i> isomer) of the two methyl groups positioned away from the copper center, while dinuclear <b>2</b>·(BF₄)₂ was only found as a symmetric (<i>io</i>–<i>io</i>) isomer, with each of the two methyl groups positioned toward different copper centers. The addition of [Cu­(MeCN)₂(DPEPhos)] (<b>3</b>·BF₄) allowed both isomers of <b>1</b>·BF₄ to form <b>2</b>·(BF₄)₂, although at different rates and via different pathways, which were analyzed using time-dependent UV–vis spectroscopy. The <i>io</i> isomer dinucleated more quickly than the <i>oo</i> isomer owing to it being able to form <b>2</b>·(BF₄)₂ (i) without bond dissociation and (ii) without a sterically congested <i>ii</i> configuration around the copper center. In contrast, <i>oo</i>-<b>1</b>·BF₄ required (i) recombination of the bipyrimidine coordination bonds or (ii) formation of a product with higher thermodynamic energy, unsymmetric (<i>ii</i>–<i>oo</i>) <b>2</b>·(BF₄)₂. These findings are interpreted as demonstrating a novel kinetic property: a conversion rate determined by pyrimidine ring inversion

Spin-Reconstructed Proton-Coupled Electron Transfer in a Ferrocene–Nickeladithiolene Hybrid

A proton–electron dual-responsive system based on a hybrid of ferrocene and metalladithiolene (<b>1</b>) was developed. The formation of the dithiafulvenium moiety was driven by protonation of the metalladithiolene unit of <b>1</b> and by oxidation. The change in the electronic structure caused by the protonation was combined with the redox properties of the two components of <b>1</b>, generating two radical species with different spin density distributions (3d spin and π spin). Furthermore, a spin-reconstructed proton-coupled electron transfer, i.e., the transformation from 3d spin to π spin accompanied by deprotonation, was achieved by a temperature change, the third external stimulus

Structural Modification on Copper(I)-pyridylpyrimidine Complexes for Modulation of Rotational Dynamics, Redox Properties, and Phototriggered Isomerization

The redox properties of copper pyridylpyrimidine complexes, which undergo linkage isomerism based on pyrimidine ring rotation, were compared under different coordination environments. A newly synthesized compound, [Cu­(Mepypm)­(L_Mes)]­BF₄ (<b>1</b>·BF₄, Mepypm = 4-methyl-2-(2′-pyridyl)­pyrimidine, L_Mes = 2,9-dimesityl-1,10-phenanthroline) was compared with previously reported complexes of [Cu­(MepmMepy)­(L_Mes)]­BF₄ (<b>2</b>·BF₄, MepmMepy = 4-methyl-2-(6′-methyl-2′-pyridyl)­pyrimidine), Cu­(Mepypm)­(DPEphos)]­BF₄ (<b>3</b>·BF₄, DPEphos = bis­[2-(diphenylphosphino)­phenyl]­ether), [Cu­(Mepypm)­(L_Anth)]­BF₄ (<b>4</b>·BF₄, L_Anth = 2,9-bis­(9-anthryl)-1,10-phenanthroline), and [Cu­(Mepypm)­(L_Macro)]­BF₄ (<b>5</b>·BF₄). Isomer ratios, isomerization dynamics, redox properties, and photoelectron conversion functions varied with the coordination structure. Methyl substituents on the 6-position of the pyridine moiety increased steric repulsion and contributed to quicker rotation, enhanced photoluminescence, and increased photodriven rotational isomerization

Structural Modification on Copper(I)-pyridylpyrimidine Complexes for Modulation of Rotational Dynamics, Redox Properties, and Phototriggered Isomerization

The redox properties of copper pyridylpyrimidine complexes, which undergo linkage isomerism based on pyrimidine ring rotation, were compared under different coordination environments. A newly synthesized compound, [Cu­(Mepypm)­(L_Mes)]­BF₄ (<b>1</b>·BF₄, Mepypm = 4-methyl-2-(2′-pyridyl)­pyrimidine, L_Mes = 2,9-dimesityl-1,10-phenanthroline) was compared with previously reported complexes of [Cu­(MepmMepy)­(L_Mes)]­BF₄ (<b>2</b>·BF₄, MepmMepy = 4-methyl-2-(6′-methyl-2′-pyridyl)­pyrimidine), Cu­(Mepypm)­(DPEphos)]­BF₄ (<b>3</b>·BF₄, DPEphos = bis­[2-(diphenylphosphino)­phenyl]­ether), [Cu­(Mepypm)­(L_Anth)]­BF₄ (<b>4</b>·BF₄, L_Anth = 2,9-bis­(9-anthryl)-1,10-phenanthroline), and [Cu­(Mepypm)­(L_Macro)]­BF₄ (<b>5</b>·BF₄). Isomer ratios, isomerization dynamics, redox properties, and photoelectron conversion functions varied with the coordination structure. Methyl substituents on the 6-position of the pyridine moiety increased steric repulsion and contributed to quicker rotation, enhanced photoluminescence, and increased photodriven rotational isomerization

Bis(dipyrrinato)zinc(II) Complexes: Emission in the Solid State

This Communication reports the first observation of solid-state photoluminescence in bis­(dipyrrinato)­zinc­(II) complexes with various substituents. The report discusses the effect of their substituents on their crystal structures and spectroscopic properties. Their <i>meso</i>-aryl groups are revealed to play important roles in the spectroscopic properties in the solid state

Bis(dipyrrinato)zinc(II) Complexes: Emission in the Solid State

This Communication reports the first observation of solid-state photoluminescence in bis­(dipyrrinato)­zinc­(II) complexes with various substituents. The report discusses the effect of their substituents on their crystal structures and spectroscopic properties. Their <i>meso</i>-aryl groups are revealed to play important roles in the spectroscopic properties in the solid state

Bis(dipyrrinato)zinc(II) Complexes: Emission in the Solid State

This Communication reports the first observation of solid-state photoluminescence in bis­(dipyrrinato)­zinc­(II) complexes with various substituents. The report discusses the effect of their substituents on their crystal structures and spectroscopic properties. Their <i>meso</i>-aryl groups are revealed to play important roles in the spectroscopic properties in the solid state

Solvent-Controlled Doublet Emission of an Organometallic Gold(I) Complex with a Polychlorinated Diphenyl(4-pyridyl)methyl Radical Ligand: Dual Fluorescence and Enhanced Emission Efficiency

A paramagnetic, luminescent organometallic gold­(I) complex Au^I(C₆F₅)­(PyBTM), where PyBTM is a photostable fluorescent polychlorinated diphenyl­(4-pyridyl)­methyl radical, was prepared, and its crystal and electronic structures and magnetic and optical properties were investigated. Magnetic studies using electron spin resonance spectroscopy and a superconducting quantum interference device magnetometer indicated the existence of <i>S</i> = ¹/₂ spin per molecule, with the spin density distributed mainly on the PyBTM ligand. The complex exhibited fluorescence in CHCl₃ with emission peak wavelength (λ_em) of 619 nm and the absolute fluorescence quantum yield (ϕ_em) of 0.04, confirming that Au^I(C₆F₅)­(PyBTM) is the first luminescent organometallic complex with a coordinated luminescent radical. Solvent-dependent unique luminescent characteristics were observed in halogenated solvents (CCl₄, CHCl₃, CH₂Cl₂, and ClCH₂CH₂Cl). ϕ_em decreased, and λ_em shifted to longer wavelengths as the polarity (dielectric constant) of the solvent increased. Notably, the complex in CCl₄ displayed fluorescence with ϕ_em = 0.23, which was quite high in radicals, while showed dual fluorescence in CH₂Cl₂ and ClCH₂CH₂Cl with lifetimes of around 1 and 7 ns for two emissive components. Density functional theory (DFT) and time-dependent (TD)-DFT calculations indicated that the fluorescence occurred from an interligand charge transfer (CT) excited state in CCl₄, in which the C₆F₅ and PyBTM moieties acted as electron donor and acceptor, respectively, while the fluorescence was centered at the PyBTM ligand in the other three solvents. This method, i.e., the formation of an interligand CT state, to enhance ϕ_em is distinctly different from the methods reported previously. The present study revealed that a coordination bond is available for forming emissive CT excited states that lead to high ϕ_em, providing a novel method with greater capability for realizing highly emissive radicals