Kazuteru Shinozaki

Luminescence color change of a platinum(II) complex solid upon mechanical grinding

The mechanochemical behavior of Pt(5dpb)Cl (5dpbH = 1,3-di(5-methyl-2-pyridyl)benzene) was investigated in terms of solid-state luminescence. The yellow luminescence of the crystalline complex changed to orange when grinding into fine powder on a glass substrate with a spatula. A broad emission band, which was not detected for the crystal, was observed at around 670 nm for the powder. The powder X-ray diffraction (XRD) pattern was the same as that calculated from X-ray crystallographic data of the single crystal. A broad band appeared within 100 ns after laser excitation accompanied by quenching of the s(pi,pi*) emission of Pt(5dpb)Cl, which was then weakened with decreasing temperature and disappeared below 120 K. The phenomenon was very similar to the excimer formation observed in solution. A related complex, Pt(dpb)Cl (dpbH = 1,3-di(2-pyridyl)benzene), also exhibited luminescent mechanochromism. However, the broad emission that appeared upon grinding still remained at 77 K, and XRD showed that the ground sample of Pt(dpb)Cl was amorphous.

Intermolecular interactions and aggregation of fac-tris(2-phenylpyridinato-C2,N)iridium(III) in nonpolar solvents.

The intermolecular interaction and aggregation of the neutral complex fac-tris(2-phenylpyridinato-C(2),N)iridium(III) (fac-Ir(ppy)3) in solution was investigated. Intermolecular interactions were found to effectively decrease the luminescence lifetime via self-quenching with increasing fac-Ir(ppy)3 concentrations. A Stern-Volmer plot for quenching in acetonitrile was linear, due to bimolecular self-quenching, but curved in toluene as the result of excimer formation. (1)H NMR spectra demonstrated a monomer-aggregate equilibrium which resulted in spectral shifts depending on solvent polarity. X-ray crystallography provided structural information concerning the aggregate, which is based on a tetramer consisting of two Δ-fac-Ir(ppy)3-Λ-fac-Ir(ppy)3 pairs. Offset π-π stacking of ppy ligands and electrostatic dipole-dipole interactions between complex molecules play an important role in the formation of these molecular pairs.

Luminescence Color Tuning of PtII Complexes and a Kinetic Study of Trimer Formation in the Photoexcited State

We investigated the luminescence properties and color tuning of [Pt(dpb)Cl] (dpbH=1,3-di(2-pyridyl)benzene) and its analogues. An almost blue emission was obtained for the complex [Pt(Fmdpb)CN] (FmdpbH=4-fluoro-1,3-di(4-methyl-2-pyridyl)benzene), modified by the introduction of F and CH3 groups to the dpb ligand and the substitution of Cl by CN. As the concentration of the solution was increased, the color of the emission varied from blue to white to orange. The color change resulted from a monomer-excimer equilibrium in the excited state. A broad emission spectrum around 620 nm was clearly detected along with a structured monomer emission around 500 nm. Upon further increases in concentration, another broad peak appeared in the longer wavelength region of the spectrum. We assigned the near-infrared band to the emission from an excited trimer generated by the reaction of the excimer with the ground-state monomer. The emission lifetimes of the monomer, dimer, and trimer were evaluated as τM =12.8 μs, τD =2.13 μs, and τT =0.68 μs, respectively, which were sufficiently long to allow association with another Pt(II) complex and dissociation into a lower order aggregate. Based on equilibrium constants determined from a kinetic study, the formation of the excimer and the excited trimer were concluded to be exothermic processes, with ΔG*D =-24.5 kJ mol(-1) and ΔG*T =-20.4 kJ mol(-1) respectively, at 300 K.

Circularly Polarized Luminescence of Chiral Pt(pppb)Cl (pppbH=1-pyridyl-3-(4,5-pinenopyridyl)benzene) Aggregate in the Excited State.

We prepared enantiomers of chiral Pt(II) complexes, Pt(pppb)Cl and Pt(pppb)CN (pppbH=1-pyridyl-3-(4,5-pinenopyridyl)benzene), and measured their CPL (circularly polarized luminescence) spectra for excimer and trimer emission. The contribution of the pinene moiety to CPL was considerably low for the π-π* emission of the monomer but large for MMLCT (metal-metal-to-ligand charge-transfer) of the excimer and trimer which had a helical structure induced in a face-to-face stacking fashion. The trimer CPL for (+)-Pt(pppb)Cl was larger in intensity than that of excimer CPL; on the other hand, that for (+)-Pt(pppb)CN was opposite in sign compared with that of excimer CPL. We conclude that differences in the excited-state structure of the aggregate between Pt(pppb)Cl and Pt(pppb)CN account for the variation in the CPL spectra. By the aid of TD-DFT calculations it was predicted that the dihedral angle θ(Cl-Pt-Pt-Cl) was 50-60° or 110-140° for Pt(pppb)Cl aggregates and 160° for Pt(pppb)CN aggregates.

Hydrophobic Hydration Structures of Tris(1, 10-phenanthroline)metal and Tris(2, 2'-bipyridine)metal Complex Ions and Effect of the Ionic Charge. X-Ray Diffraction Study with Isomorphous Substitution

X-Ray diffraction measurements have been made for aqueous solutions of sulfates or chlorides of [Ru(phen)3]2+, [Ni(phen)3]2+, [Ru(bpy)3]2+, [Ni(bpy)3]2+, [Rh(bpy)3]3+, and [Cr(bpy)3]3+ (phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine). Radial distribution functions for the metal interactions were obtained by the isomorphous substitution between ruthenium(II) and nickel(II) complexes or between rhodium(III) and chromium(III) complexes. Metal–nitrogen and metal–carbon distances within the complex ions in solution were essentially in agreement with those in the crystals. Regarding the divalent metal complexes, about two water molecules seemed to exist at a distance of 3.5—3.6 A (1 A = 10−10 m) from the central metal atom and 10—11 water molecules existed in the region of 5.3 to 6.3 A, probably in the vicinity of peripheral hollows along the C3 axis of the complex. Further, large broad peaks with high electron density were observed around 7.7 and 11.2 A for the [Ru(bpy)3]2+ ion and around 8.0 and 11.5 A for...

[2,6-Bis(5-methyl-2-pyridyl)phenyl-κ3N,C1,N′]chloridoplatinum(II)

In the title compound, [Pt(C(18)H(15)N(2))Cl], the Pt(II) centre adopts a distorted square-planar coordination geometry due to the pincer-type monoanionic N-C-N tridentate ligand. The planar complexes stack via pi-pi interactions to form two-dimensional accumulated sheets. This packing pattern is in contrast to that in related pincer-type N-C-N complexes, which exhibit a one-dimensional columnar stacking.

X-ray diffraction study on the aggregate structure of 5,10,15,20-tetra(4-sulfophenyl)porphinatopalladium(II)(4-) in aqueous solution

The aggregate structure of 5,10,15,20-tetra(4-sulfophenyl)porphinatopalladium(II) ion (PdTPPS4–) in aqueous solution has been investigated in terms of the distance between the porphyrin monomers, by use of absorption spectroscopy, paramagnetic relaxation of NMR signals, and an isomorphic substitution method for X-ray diffraction of the solution. From absorption spectroscopy results it was concluded that the aggregate was regarded as a dimer arising from hydrophobic attraction between the porphyrin rings. Paramagnetic effects on the longitudinal relaxation time (T1) for 13C NMR of PdTPPS4– by the addition of 5,10,15,20-tetra(4-sulfophenyl)porphinatocopper(II)(CuTPPS4–) suggested that the paramagnetic centre was located along a C4-axis of PdTPPS4– in a PdTPPS4––CuTPPS4– dimer. The dimer of PdTPPS4– was determined to have a twisted face-to-face stacked structure (D4d) at a distance of 4.1 A by the isomorphic substituted X-ray diffraction study on PdTPPS4– and CuTPPS4– solutions.

Radical formation of 5,10,15,20-tetra(4-sulfophenyl) porphinatopalladium(II)(4 -) in the lowest excited triplet states

Abstract Excited 5,10,15,20-tetra(4-sulfopheny)porphinatopalladium(II) (PdTPPS 4− ) was studied by phosphorescence lifetime, phosphorescence quenching, delayed fluorescence, and transient absorption measurements in terms of the dimerization reaction. Lifetimes of monomer and dimer was determined as τ =360 and 270 μs, respectively. The self-association rates of PdTPPS 4− in the excited and ground states are the same. Transient absorption unveiled the radical formation resulted from the charge separation after photo excitation.

X-Ray Diffraction Study of the Solvation Structure of the Cobalt(II) Ion in N,N-Dimethylformamide Solution

Abstract The solvation structure of Co2+ in N,N-dimethylformamide (DMF) has been studied by X-ray diffraction measurements on cobalt (II) and magnesium (II) Perchlorate solutions of the same concen tration, using an isostructural substitution method. The radial distribution function revealed three distinct peaks assigned to the oxygen, amido carbon (C1, and nitrogen atoms of six planar DMF molecules in the first coordination sphere around the metal atom. The distance from the cobalt atom to each atom (O, C1, N) is 213,299, and 423 pm, respectively. This indicates that the Co-O-C1 bond angle is 122-123° and the metal atom is close to the O-C1-N plane of the DMF molecule.