Formation of Hetero-binuclear Pt(II)-M(II) Complexes Based on (2-(1 H-Tetrazol-5-yl)phenyl)diphenylphosphine Oxide for Superior Phosphorescence of Monomers

A cyclometalated Pt(II)-Pt(II) clamshell dimer with a triplet emission at 887 nm

Here, a cyclometalated Pt(II) clamshell dimer (complex 2) has been synthesized with the primary ligand of dibenzo(f,h)quinoxaline and an ancillary ligand of N,N'-diphenylformamidine. In addition, a mononuclear Pt(II) complex 1a and a binuclear Pt(II) complex 1b were also prepared. Complex 1a was coordinated by one cyclometalated ligand of dibenzo(f,h)quinoxaline, one chloride ion, and one N,N'-diphenylformamidine. Complex 1b was coordinated by one cyclometalated ligand of dibenzo(f,h)quinoxaline, two chloride ions, and two N,N'-diphenylformamidines. All of these three complexes were characterized by nuclear magnetic resonance (NMR) spectroscopy, high-resolution mass spectrometry (HRMS), elemental analyses, and single-crystal X-ray diffraction (XRD). The Pt-Pt distance in complex 2 was 2.8439(2) Å. It also exhibited a near-infrared (near-IR) emission at 887 nm in the pure solid state. On the other hand, complexes 1a and 1b exhibited triplet emission at 589 and 660 nm, respectively, in the pure solid state. Furthermore, in 2 wt% poly(Me methacrylate) (PMMA) films, complex 1a showed a triplet emission at 548 nm (with Φ = 84% and τ = 5.53 μs) and complex 1b showed an emission at 627 nm (with Φ = 79% and τ = 4.07 μs). Due to its great photophysical properties, complex 1b was deposited onto quartz plates for the detection of organic solvent vapors and it showed unique emission quenching for the vapor of tetrahydrofuran.

Efficiently luminescent heteroleptic neutral platinum(II) complexes based on N^O and N^P benzimidazole ligands

A series of new luminescent cycloplatinated(II) complexes (5a-8a and 5b-8b) with formulas Pt(bt)(N^O) and Pt(bt)(N^P) have been synthesized [bt = phenylbenzothiazole, N^O = (2-(1H-benzimidazole)-phenyl)diphenylphosphine oxide derivatives for 1a-4a and N^P = (2-(1H-benzimidazole)-phenyl)diphenylphosphine derivatives for 1b-4b]. The crystal structures of the complexes show distorted square planar geometries around the platinum centers. There are no obvious π-π and Pt-Pt intermolecular interactions in the crystal lattice due to the presence of sterically bulky ancillary ligands. Consequently, these complexes exhibit structured monomeric emissions in the range of 527-540 nm in CH₂Cl₂ solution. The photoluminescent quantum yields of Pt(bt)(N^O) (5a-8a) in CH₂Cl₂ solution at room temperature are higher than those of Pt(bt)(N^P) (5b-8b). The above result is well consistent with the crystal structural characteristics of the complexes. The structured emission with microsecond radiative lifetimes and the result of TD-DFT calculations indicate that the emissions of these complexes are mainly attributed to a mixed ³LC-MLCT state.

A Carbazole-Bridged Biscyclometalated Diplatinum Complex: Synthesis, Characterization, and Dual-Mode Aggregation-Enhanced Phosphorescence

A cationic carbazole-bridged biscyclometalated diplatinum complex 4 has been synthesized and characterized. Single-crystal X-ray analysis demonstrates that complex 4 displays a dimeric structure with noncovalent π-π stacking and unique double Pt-Pt interactions. In aerated dilute CH₃CN, complex 4 is characterized by a very weak monomeric yellow emission (λ_emi = 547 nm; Φ = 0.51%), which is attributed to the triplet intraligand (³LC) excited state mixing with some charge transfer characters. In contrast, under aerated conditions, the dispersion of 4 in a mixed solvent of CH₃CN/Et₂O (1/9, v/v) or CH₃CN/H₂O (1/9, v/v) displays intense yellow (λ_emi = 550 nm; Φ = 35.5%; τ = 11.10 μs) and red emission (λ_emi = 635 nm; Φ = 14.1%; τ = 7.00 μs), respectively. These aggregation-induced phosphorescent emission enhancements are considered being caused by the oxygen-shielding effect and the molecular rigidification-induced decrease of nonradiative decays in the aggregate state. The morphology and size of the aggregates under these two conditions are examined by scanning electron microscope and dynamic light scattering analysis. The absorption and emission properties of 4 are further rationalized by time-dependent density functional theory calculations on a model compound.

Nickel-catalyzed C–P cross-coupling of (het)aryl tosylates with secondary phosphine oxides

A novel and convenient approach to the synthesis of various tertiary phosphine oxides via nickel-catalyzed cross-coupling of (het)aromatic tosylates with secondary phosphine oxides is developed. The reaction employs cheap nickel as the catalyst, 1-(2-(di-tert-butylphosphanyl)phenyl)-4-methoxypiperidine (L3) as the ligand, and pyridine as the base. This reaction produces the corresponding (het)aromatic phosphorus compounds in good to high yields. Moreover, four new tertiary phosphine oxides are reported in this process.