Circularly Polarized Phosphorescence Properties of Binuclear Cyclometalated Platinum(II) Complexes Bearing Axially Chiral Schiff-Base Ligands.

The synthesis, structure, and circularly polarized phosphorescence (CPP) properties of axially chiral cyclometalated binuclear platinum(II) complexes were described. A series of optically pure binuclear platinum(II) complexes were synthesized in five steps from commercially available ()- or ()-1,1'-bi-2-naphthol (BINOL) as starting materials. Their three-dimensional molecular structures and square-planar coordination geometries were elucidated from X-ray diffraction and 2D NMR analysis.

Colour/luminescence changes of transition metal complexes induced by gaseous small molecules for monitoring reaction progress and environmental changes.

Transition metal complexes act as monitoring devices for reaction progress and environmental changes through their color/luminescence changes. In this paper, we focus on colour/luminescence changes induced by gaseous small molecules in the environment. The gradual decrease in O content in solution can be monitored by the luminescence enhancement of an Ir(III) complex in dimethyl sulfoxide during photoirradiation.

Sequential H/D Exchanges Resulting from Rollover-Cyclometallation during Photoirradiation of Rhodium(III) Complex in Methanol-d.

We present the photoreaction of newly prepared bis(6,6'-dimethyl-2,2'-bipyridine)(oxalato)rhodium(III) ([Rh(N N)(ox)]) in CDOD. Photoirradiation of this complex causes the dissociation of ox, followed by the formation of the unprecedented Rh(III) complex with Rh-H and Rh-C σ bonds, [Rh(N N)(C N)(H)(CDOD)] (C N=[6,6'-dimethyl-2,2'-bipyridine]-3-yl-κC,κN). This hydride formation and cyclometallation spontaneously proceed owing to the conflict between the steric hindrance arising from the methyl groups of N N and the driving force for the structural change due to [Rh(N N)] formation.

Photodynamic Effect of Amphiphilic NCN-Coordinated Platinum(II) Complexes in Human Umbilical Vein Endothelial Cells.

Here, we report a photodynamic therapy (PDT) photosensitizer of NCN-coordinated Pt(II) complexes: [Pt(L)(solv)] (HL = 1,3-(2-dipyridyl)benzene) and [Pt(L)]@HSA, which is the Pt(II) complex encapsulated in human serum albumin (HSA). The quantum yield of singlet oxygen production for [Pt(L)(solv)] is more than 50%, while that for [Pt(L)]@HSA is much lower. Photoimages of human umbilical vein endothelial cells (HUVECs) treated with the Pt(II) complexes suggest that [Pt(L)(solv)] is delocalized in the entire cell after the fast uptake by diffusion and [Pt(L)]@HSA is taken up by endocytosis and localized on organelles and the cell membrane.

Circularly polarized phosphorescence with a large dissymmetry factor from a helical platinum(II) complex.

A chiral platinum(II) complex with a helical Schiff-base [4]helicene ligand exhibits intense red circularly polarized phosphorescence (CPP) with a of 0.010 in the dilute solution state. The intense CPP was caused by a change in the electronic transition character based on the induction of the helical structure.

Assembling of a Water-Soluble N^C^N-Coordinated Pt(II) Complex Aggregate Assisted by Carbon Dioxide in Basic Aqueous Solution.

We report an unprecedented result of self-aggregation of [Pt(L )Cl] (HL =1,3-di(5-carboxy-2-pyridyl)benzene) triggered by CO in basic aqueous solution. The color of basic aqueous solution containing [Pt(L )Cl] changes from yellow to blue-green during the aggregation resulted from a reaction with CO in air. Upon CO gas bubbling, strong and broad absorption bands of aggregate assigned to the metal-metal-to-ligand charge-transfer transition appeared at 701 and 1152 nm.

Kinetic Formation of Pt-Pt Dimers of Cationic and Neutral Platinum(II) Complexes under Rapid Freeze Conditions in Solution.

We report the formation of M-M dimers (M = Pt or Pd) of cationic [M(dpb)(CHCN)] [dpbH = 1,3-di(2-pyridyl)benzene] and neutral [M(dpb)Cl] complexes resulting from the rapid freezing of solutions. Dimers based on M-M dz overlap were found to preferentially form rather than the thermodynamically favored head-to-tail π-stacking structures typically observed in the crystalline state. Kinetic dimers in glassy frozen solutions generated broad metal-metal-to-ligand charge-transfer emissions within the range of 600-800 nm at 77 K.

Luminescence color change of [3,4-difluoro-2,6-bis(5-methyl-2-pyridyl)phenyl-κ,,']cyanidoplatinum(II) by aggregation.

We have investigated the color and luminescence color changes of novel Pt(L)CN (L = 4,6-difluoro-1,3-di(2-(4-methyl)pyridyl)benzene) in solution and crystalline states that resulted from aggregation-induced emission (AIE). In the solution state, the AIE results from excimer and trimer formation in the excited states at high concentrations. We determined the emission lifetimes of the excimer and trimer to be = 1.

Vapochromism of an iridium(III) bis-terpyridine complex based on the modulation of halide-to-ligand charge transfer transition.

We report, for the first time, a color change originating from the shift of the halide-to-ligand charge transfer (XLCT) band of the Ir(III) bis-terpyridine complex crystal in response to the sorption/desorption of water of crystallization. Red and orange coloration reversibly takes place by heat and cool treatments, respectively. Single X-ray crystallography shows that the Ir(III) complex possesses two waters of crystallization constructing a dimer structure, = 2.

Reversible colour/luminescence colour changes of tetracyanoruthenium(II) complexes by sorption/desorption of water molecules in crystals.

We report colour/luminescence colour changes of M[Ru(bpy)(CN)] crystal (M = Ca, Sr, and Ba; bpy = 2,2'-bipyridine). The X-ray crystallographic study revealed that the crystals are constructed from linear-chains of {[Ru(bpy)(CN)][Ca(HO)]}, {[Ru(bpy)(CN)][Sr(HO)]}, and {[Ru(bpy)(CN)][Ba(HO)](μ-HO)}, respectively. Ru(II) complex linear chains and the hydrophilic channels composed of M ion and water along them enable reversible water sorption/desorption without collapse of crystals responsible for the colour change.

Emission Intensity Enhancement for Iridium(III) Complex in Dimethyl Sulfoxide under Photoirradiation.

We found emission intensity enhancement for -Ir(ppy) (ppy = 2-(2'-phenyl)pyridine) in aerated dimethyl sulfoxide (DMSO) during photoirradiation for the first time. This phenomenon was concluded to be responsible for the consumption of O dissolved in DMSO through dimethyl sulfone production by photosensitized reaction using -Ir(ppy). A O adduct of DMSO molecule was detected by UV absorption measurement and theoretical calculation.

Vortex-Induced Harmonic Light Scattering of Porphyrin J-Aggregates.

An understanding of macroscopic vortex-induced chirality can provide insights into the origin of the homochirality of life. While circular dichroism measurements in stirred solutions are useful for the analysis of chiral supramolecular structures induced by vortex motion, there are no reports on the application of other spectroscopic methods. To obtain a deeper understanding of macroscopic vortex-induced chirality, it is essential to develop novel spectroscopic methods that provide information about changes in both the size and chirality in stirred solutions.

Dual emission from an iridium(III) complex/counter anion ion pair.

[Ir(tpy)2](PF6)3 (tpy = 2,2':6',2''-terpyridine) dissolved in CH3CN was found to exhibit dual color luminescent emission depending on the excitation wavelength. Specifically, blue and green emissions were obtained with excitation at 350 and 410 nm, respectively. Because the associated emission spectra were consistent with those of [Ir(tpy)2]Cl3 in water and [Ir(tpy)2](PF6)3 in the crystalline state, respectively, this dual emission is attributed to emissions from the [Ir(tpy)2]3+ cation and its ion pair [Ir(tpy)2]3+·PF6-.

Discovery of Amorphous Iron Hydrides via Novel Quiescent Reaction in Aqueous Solution.

Novel amorphous iron hydrides (AIHs) are synthesized for the first time under ambient conditions by employing novel "quiescent reaction", without stirring for mixing solutions, during a conventional aqueous reduction-precipitation process. The kind and morphology of AIHs are dependent on the processing condition, where two types are found, with one form consisting of a tangle of uniform nanowires and the other being granular in nature. Both AIHs undergo transformation to crystalline α-Fe by heat treatment at 600 °C.

H/D solvent isotope effects on the photoracemization reaction of enantiomeric the tris(2,2'-bipyridine)ruthenium(ii) complex and its analogues.

This work assessed solvent isotope effects on the photoracemization rate and emission lifetime for [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) in water. An analysis of the effects of temperature on photoracemization rate and emission lifetime demonstrated that the transition from one enantiomer to the other is unaffected by the isotopic composition of the solvent. The results also showed that deactivation from the metal-to-ligand charge-transfer (3MLCT) excited state to the ground state is responsible for the solvent isotope effect on the photoracemization rate.

Highly Selective Aluminum(III) Ion Sensing with Luminescent Iridium(III) Complexes Bearing a Distorted 2,2'-Bipyridine-3,3'-diol Moiety Utilizing a Rigidified Seven-Membered Chelate Ring.

To create an ion sensor utilizing a rigidified seven-membered chelate ring, we developed two Ir(III) complexes with 2,2'-bipyridine-3,3'-diol (bpy(OH), ) ligands as reaction centers, namely ([Ir(ppy){bpy(O)(OH)}], ppy = 2-phenylpyridine) and ([Ir(bzq){bpy(O)(OH)}], bzq = benzo[]quinoline), and evaluated their reactivities toward metal ions by spectrophotometry. When they are reacted with Al, these complexes exhibit dramatic enhancements in emission intensity (775-fold for and 51.0-fold for ) and distinct orange to green changes in emission color.

A stochastic analysis based on a one-dimensional random walk model of the persistent phosphorescence of Mn ions doped in zinc magnesium phosphate.

We investigate the mechanism of the persistent phosphorescence (PP) of β-Zn3(PO4)2:Mn2+ and γ-(Zn2+,Mg2+)3(PO4)2:Mn2+ systems via stochastic analysis. An electron hopping mechanism, recombining electrons with Mn3+ ions, is proposed to elucidate the long-tailed decay feature that represents a non-exponential decay curve for the PP intensity change over time. A simulation using a one-dimensional random walk for the electron hopping in the host material successfully reproduces the PP decay curve.

Optical Resolution, Determination of Absolute Configuration, and Photoracemization of cis-RuL2(CN)2 (L = 2,2'-Bipyridine and Its Analogues).

We synthesized neutral Ru(II) complexes cis-Ru(bpy)2(CN)2 (bpy = 2,2'-bipyridine), cis-Ru(dmb)2(CN)2 (dmb = 4,4'-dimethyl-2,2'-bipyridine), cis-Ru(dbb)2(CN)2 (dbb = 4,4'-di-tert-butyl-2,2'-bipyridine), and cis-Ru(phen)2(CN)2 (phen = 1,10-phenanthroline) and optically resolved them into respective enantiomers using high-performance liquid chromatography with a chiral column. The absolute configuration of enantiomer of cis-Ru(dbb)2(CN)2 was determined by an X-ray crystallography. Upon photoirradiation, the entire enantiomers of the complexes underwent the racemization with considerably slow rates (k = 1 × 10(-6) to 1 × 10(-5) s(-1)) and small quantum yields (ϕ = 1 × 10(-6) to 1 × 10(-5)).

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.

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.

Luminescence change by the solvent of crystallization, solvent reorganization, and vapochromism of neutral dicyanoruthenium(II) complex in the solid state.

The "solvent effect" on the solid-state luminescence of a neutral complex, [Ru(dbb)(2)(CN)(2)] (dbb = 4,4'-di-tert-butyl-2,2'-bipyridine), was presented. The crystals of this complex showed a variety of luminescence color from orange to dark-red, depending on the acceptor number of the solvent included in the crystal as a solvent of crystallization. The luminescence change was very similar to the solvatochromism in solution, which was attributed to the local donor-acceptor interaction between the CN group and the solvent molecules.

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.

[2,6-Bis(5-methyl-2-pyridyl)phenyl-kappa(3)N,C(1),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.

Quantitative analysis of long-range interactions between adsorbed dipolar molecules on Cu(111).

Highly dispersed superstructures of a dipolar iridium complex are formed on a Cu(111) surface. We show that the dilute superstructures with density-controlled intermolecular separations are stabilized by the strong and long-range repulsive intermolecular interactions. The repulsive intermolecular interactions are quantitatively evaluated by using low-temperature scanning tunneling microscopy, which are characterized by the surface-enhanced dipole-dipole interactions.

Tuning of luminescence spectra of neutral ruthenium(II) complexes by crystal waters.

Neutral ruthenium(II) complexes [RuLL'(CN)2] (L, L' = bpy, dmb, dbb; bpy = 2,2'-bipyridine, dmb = 4,4'-dimethyl-2,2'-bipyridine, dbb = 4,4'-tert-butyl-2,2'-bipyridine) were prepared, and the luminescence characteristics of the complexes in the solid state were measured. The luminescence was tuned by crystal waters included in the crystals; for example, [Ru(dbb)2(CN)2] x 2H2O, [Ru(dbb)2(CN)2] x H2O, and [Ru(dbb)2(CN)2] emit luminescence at 640, 685, and 740 nm, respectively.