Synthesis and Photophysical Properties of Monometallic C

A novel class of cyclometalated platinum(II) complexes-previously considered to be inaccessible-was synthesized by an improved synthetic route utilizing ligands predicted by density functional theory calculations. Based on a concise quantum chemical screening three model ligands with varying steric demand were chosen and a series of six photoluminescent C^C* cyclometalated platinum(II) formamidinate complexes was obtained. The least sterically demanding ligand led to a bimetallic complex in two isomeric forms, which could be separated and confirmed by the corresponding solid-state structures. Sterically more hindered amidinate ligands gave the monometallic complexes supporting the theoretical predictions. The monometallic complexes show a significant hypsochromic shift of the emission wavelength, explained by the loss of the metal-metal interactions. Depending on the cyclometalating ligand quantum yields up to 87 % with short decay times were found for this new class of phosphorescent green-blue to pure blue platinum(II) emitters.

Electronic Structure and Magnetic Properties of a High-Spin MnIII Complex: [Mn(mesacac)3 ] (mesacac=1,3-Bis(2,4,6-trimethylphenyl)-propane-1,3-dionato).

Metal acetylacetonates of the general formula [M(acac)3 ] (MIII =Cr, Mn, Fe, Co) are among the best investigated coordination compounds. Many of these first-row transition metal complexes are known to have unique electronic properties. Independently, photophysical research with different ß-diketonate ligands pointed towards the possibility of a special effect of the 2,4,6-trimethylphenyl substituted acetylacetonate (mesacac) on the electron distribution between ligand and metal (MLCT). We therefore synthesized and fully characterized the previously unknown octahedral title complex. Its solid-state structure shows a Jahn-Teller elongation with two Mn-O bonds of 2.12/2.15 Šand four Mn-O bonds of 1.93 Å. Thermogravimetric data show a thermal stability up to 270 °C. High-resolution mass spectroscopy helped to identify the decomposition pathways. The electronic state and spin configuration of manganese were characterized with a focus on its magnetic properties by measurement of the magnetic susceptibility and triple-zeta density functional theory (DFT) calculations. The high-spin state of manganese was confirmed by the determination of an effective magnetic moment of 4.85 µB for the manganese center.

Phosphorescent Bimetallic C

A series of phosphorescent bimetallic platinum(II) complexes is presented, which were synthesized by the combination of bidentate cyclometalated N-heterocyclic carbene ligands and different bridging diphenylformamidinates. The complexes were characterized by standard techniques and additionally two solid-state structures could be obtained. Photoluminescence measurements revealed the strong emissive behavior of the compounds with quantum yields of up to 90 % and emission lifetimes of approx. 2 µs. The effect of the substitution pattern in the bridging ligands on the structural and photophysical properties of the complexes was examined in detail and rationalized by density functional theory calculations (PBE0/6-311G*).

Cyclometalated Spirobifluorene Imidazolylidene Platinum(II) Complexes with Predominant 3LC Emissive Character and High Photoluminescence Quantum Yields.

Two novel bidentate C^C*spiro cyclometalated platinum(II) complexes comprising a spiro-conjugated bifluorene ligand and different ß-diketonate auxiliary ligands are synthesized and characterized. Their preparation employs a robust and elaborate synthetic protocol commencing with an N-heterocyclic carbene precursor. Structural characterization by means of NMR techniques and solid-state structures validate the proposed and herein presented molecular scaffolds. Photophysical studies, including laser flash photolysis methods, reveal an almost exclusively ligand-centered triplet state, governed by the C^C*spiro-NHC ligand. The high triplet energies and the long triplet lifetimes in the order of 30 µs in solution make the complexes good candidates for light-emitting diode-driven photocatalysis, as initial energy transfer experiments reveal. In-depth time-dependent density functional theory investigations are in excellent accordance with our spectroscopic findings. The title compounds are highly emissive in the bluish-green color region with quantum yields of up to 87% in solid-state measurements.

C

The combination of strong electron-withdrawing groups in cyclometalated N-heterocyclic carbene ligands (C^C*) with known beneficial auxiliary ligands in phosphorescent platinum(II) complexes leads to efficient light-to-deep-blue emission with quantum yields of up to 92%. All compounds were characterized and investigated regarding their photophysical, electrochemical, and thermal properties, and three complexes could additionally be characterized by solid-state structures. Density functional theory calculations (PBE0/6-311G* with dispersion correction) are reported.

Platinum(II) Complexes with Bis(pyrazolyl)borate Ligands: Increased Molecular Rigidity for Bidentate Ligand Systems.

The structural motif of platinum(II) complexes bearing cyclometalating N-heterocyclic carbene ligands can be used to design deep-blue phosphors for application in organic light-emitting diodes. However, the photophysical properties of the resulting molecules are also highly dependent on the auxiliary ligand. These often allow molecular deformations in the excited state which contribute to non-radiative decay processes that diminish the attainable quantum yield. The use of bis(pyrazolyl)borate-based auxiliary ligands enforces a high molecular rigidity due to their unique geometry. The steric crowding in the coordination sphere inhibits deformation processes and results in highly efficient deep-blue platinum(II) emitters with CIE coordinates below (0.15; 0.15).

Iron-Catalyzed Synthesis, Structure, and Photophysical Properties of Tetraarylnaphthidines.

We describe the synthesis and photophysical properties of tetraarylnaphthidines. Our synthetic approach is based on an iron-catalyzed oxidative C-C coupling reaction as the key step using a hexadecafluorinated iron-phthalocyanine complex as a catalyst and air as the sole oxidant. The N,N,N',N'-tetraarylnaphthidines proved to be highly fluorescent with quantum yields of up to 68%.