Photophysical Properties of Simple Palladium(0) Complexes Bearing Triphenylphosphine Derivatives.

Pd(0) complexes with monodentate phosphine ligands, [Pd(P)n] (n = 3, 4), are well-known catalysts. However, the nature of the Pd(0) complex, especially the basic photophysical properties of the Pd(0) complexes, has not been extensively explored. In this work, we measured the general photophysical properties and crystal structures of Pd(0)-bearing PPh3 derivatives in the solid state and in solution. In the solid state, four-coordinated Pd(0) complexes exhibited blue-yellow emission. On the other hand, three-coordinated Pd(0) complexes displayed yellow-orange emission. In solution, orange emission of three-coordinated complexes was observed, and prompt fluorescence was detected using time-resolved emission spectroscopy, which suggests a thermally activated delayed fluorescence mechanism. Density functional theory (DFT) and time-dependent DFT calculations show that the difference in the transition mechanism between the [Pd(PPh3)4] and [Pd(PPh3)3] complexes explains the different emission colors. The emitting states of both complexes have metal-to-ligand charge-transfer character, but the metal-centered d → p transition is considerably incorporated for emission of the tris complex.

Self-assembly as a key player for materials nanoarchitectonics.

The development of science and technology of advanced materials using nanoscale units can be conducted by a novel concept involving combination of nanotechnology methodology with various research disciplines, especially supramolecular chemistry. The novel concept is called 'nanoarchitectonics' where self-assembly processes are crucial in many cases involving a wide range of component materials. This review of self-assembly processes re-examines recent progress in materials nanoarchitectonics. It is composed of three main sections: (1) the first short section describes typical examples of self-assembly research to outline the matters discussed in this review; (2) the second section summarizes self-assemblies at interfaces from general viewpoints; and (3) the final section is focused on self-assembly processes at interfaces. The examples presented demonstrate the strikingly wide range of possibilities and future potential of self-assembly processes and their important contribution to materials nanoarchitectonics. The research examples described in this review cover variously structured objects including molecular machines, molecular receptors, molecular pliers, molecular rotors, nanoparticles, nanosheets, nanotubes, nanowires, nanoflakes, nanocubes, nanodisks, nanoring, block copolymers, hyperbranched polymers, supramolecular polymers, supramolecular gels, liquid crystals, Langmuir monolayers, Langmuir-Blodgett films, self-assembled monolayers, thin films, layer-by-layer structures, breath figure motif structures, two-dimensional molecular patterns, fullerene crystals, metal-organic frameworks, coordination polymers, coordination capsules, porous carbon spheres, mesoporous materials, polynuclear catalysts, DNA origamis, transmembrane channels, peptide conjugates, and vesicles, as well as functional materials for sensing, surface-enhanced Raman spectroscopy, photovoltaics, charge transport, excitation energy transfer, light-harvesting, photocatalysts, field effect transistors, logic gates, organic semiconductors, thin-film-based devices, drug delivery, cell culture, supramolecular differentiation, molecular recognition, molecular tuning, and hand-operating (hand-operated) nanotechnology.

Materials Nanoarchitectonics for Mechanical Tools in Chemical and Biological Sensing.

In this Focus Review, nanoarchitectonic approaches for mechanical-action-based chemical and biological sensors are briefly discussed. In particular, recent examples of piezoelectric devices, such as quartz crystal microbalances (QCM and QCM-D) and a membrane-type surface stress sensor (MSS), are introduced. Sensors need well-designed nanostructured sensing materials for the sensitive and selective detection of specific targets. Nanoarchitectonic approaches for sensing materials, such as mesoporous materials, 2D materials, fullerene assemblies, supported lipid bilayers, and layer-by-layer assemblies, are highlighted. Based on these sensing approaches, examples of bioanalytical applications are presented for toxic gas detection, cell membrane interactions, label-free biomolecular assays, anticancer drug evaluation, complement activation-related multiprotein membrane attack complexes, and daily biodiagnosis, which are partially supported by data analysis, such as machine learning and principal component analysis.

Photophysical properties of three coordinated copper(i) complexes bearing 1,10-phenanthroline and a monodentate phosphine ligand.

We report the synthesis and photophysical properties of Cu(i) complexes with 1,10-phenanthroline (phen) and monodentate phosphine ligands. Single crystal X-ray structural analysis revealed that these have three-coordinated trigonal planar geometries. We also found that one of them, [Cu(phen)(Johnphos)]BF4 (Johnphos = 2-(di-tert-butylphosphino)biphenyl), is considerably emissive both in solution and solid states. The emission maximum wavelength of the emission of the complex is 580 nm, and the lifetime of the emission is 2 µs in solution. Moreover, we have systematically investigated the photophysical and redox properties of four-coordinate complexes [Cu(NN)(P)2]+ in addition to three-coordinate complexes [Cu(NN)(P)]+. Charge transfer transitions play a key role in the photophysics of these complexes.

Crystal structure of [N,N-bis-(di-phenyl-phospho-ro-thio-yl)amidato-κ2S,S']bis-(tri-phenyl-phosphane-κP)copper(I) di-chloro-methane monosolvate.

The title compound, [Cu(C24H20NP2S2)(C18H15P)2]·CH2Cl2 or [Cu(dppaS2)(PPh3)2]·CH2Cl2, is a neutral mononuclear copper(I) complex bearing an N,N-bis-(di-phenyl-phospho-rothio-yl)amidate (dppaS2-) ligand and two tri-phenyl-phosphane ligands. The molecular structure shows that the two S atoms of the dppaS2- ligand [Cu-S = 2.3462 (9) and 2.3484 (9) Å] and the two P atoms of the two tri-phenyl-phosphane ligands [Cu-P = 2.3167 (9) and 2.2969 (9) Å] coordinate to the copper(I) atom, resulting in a tetra-hedral coordination geometry. The crystallographically observed mol-ecular structure is compared to the results of DFT calculations.

Coordination Nanosheets Based on Terpyridine-Zinc(II) Complexes: As Photoactive Host Materials.

Photoluminescent coordination nanosheets (CONASHs) comprising three-way terpyridine (tpy) ligands and zinc(II) ions are created by allowing the two constitutive components to react with each other at a liquid/liquid interface. Taking advantage of bottom-up CONASHs, or flexibility in organic ligand design and coordination modes, we demonstrate the diversity of the tpy-zinc(II) CONASH in structures and photofunctions. A combination of 1,3,5-tris[4-(4'-2,2':6',2″-terpyridyl)phenyl]benzene (1) and Zn(BF4)2 affords a cationic CONASH featuring the bis(tpy)Zn complex motif (1-Zn), while substitution of the zinc source with ZnSO4 realizes a charge-neutral CONASH with the [Zn2(µ-O2SO2)2(tpy)2] motif [1-Zn2(SO4)2]. The difference stems from the use of noncoordinating (BF4-) or coordinating and bridging (SO42-) anions. The change in the coordination mode alters the luminescence (480 nm blue in 1-Zn; 552 nm yellow in 1-Zn2(SO4)2). The photophysical property also differs in that 1-Zn2(SO4)2 shows solvatoluminochromism, whereas 1-Zn does not. Photoluminescence is also modulated by the tpy ligand structure. 2-Zn contains triarylamine-centered terpyridine ligand 2 and features the bis(tpy)Zn motif; its emission is substantially red-shifted (590 nm orange) compared with that of 1-Zn. CONASHs 1-Zn and 2-Zn possess cationic nanosheet frameworks with counteranions (BF4-), and thereby feature anion exchange capacities. Indeed, anionic xanthene dyes were taken up by these nanosheets, which undergo quasi-quantitative exciton migration from the host CONASH. This series of studies shows tpy-zinc(II) CONASHs as promising potential photofunctional nanomaterials.

Crystal structure of bis-[µ-1,4-bis-(di-phenyl-phos-phan-yl)butane-κ2P:P']bis-[(3,4,7,8-tetra-methyl-1,10-phenanthroline-κ2N,N')copper(I)] bis-(hexa-fluorido-phosphate) di-chloro-methane disolvate.

The dication of the title compound, [Cu2(C28H28P2)2(C16H16N2)2](PF6)2·2CH2Cl2, has crystallographically imposed inversion symmetry. The copper(I) cation is coordinated in a distorted tetra-hedral geometry by two N atoms of a chelating 3,4,7,8-tetra-methyl-1,10-phenanthroline ligand and two P atoms of two bridging 1,4-bis-(di-phenyl-phosphan-yl)butane ligands, forming a 14-membered ring. An intra-molecular π-π inter-action stabilizes the conformation of the dication. In the crystal, dications are linked by π-π inter-actions involving adjacent phenanthroline rings, forming chains running parallel to [111]. Weak C-H⋯F hydrogen inter-actions are also observed.

Emission properties and Cu(i)-Cu(i) interaction in 2-coordinate dicopper(i)-bis(N-heterocyclic)carbene complexes.

The synthesis, characterization, and emission properties of 2-coordinate dicopper(i) complexes bearing two trimethylene-bridged bis-NHC ligands, [Cu2(L3Me)2](PF6)2 (1), [Cu2(L3Et)2](PF6)2 (2), [Cu2(L3Bu)2](PF6)2 (3), [Cu2(L3MeOPh)2](PF6)2 (4) and [Cu2(L3Mes)2](PF6)2 (5), where L3R denotes trimethylene-bridged bis(N-heterocyclic)carbene (NHC) ligand substituted by two R groups at the nitrogen atoms of NHC, have been investigated. The quantum yield, Φ, and the lifetime, τ, of the emission of 2, are 0.21 and 25 µs, respectively in methanol, which is a well-known solvent for quenching the luminescence of many copper(i) complexes. The 8-shaped geometry of the dicopper(i) complexes brings a considerable copper(i)-copper(i) interaction which affects the luminescent properties. Additionally, we find that methoxyphenyl and mesityl groups substituted at the nitrogen atom of the NHC moiety drastically stabilize the bis(NHC) copper(i) complexes even in air-saturated acetone-d6.

Conformational and Optical Characteristics of Unidirectionally Twisted Binaphthyl-Bipyridyl Cyclic Dyads.

An axially chiral binaphthyl-bipyridyl cyclic dyad in which the two units are connected by short -CH2O- linkers was synthesized. Experimental and theoretical analyses indicate that the (R)-binaphthyl unit in the dyad induces (R)-chirality in the bipyridyl unit, both in the solid state and in solution. It is shown that vibrational circular dichroism (VCD) is useful to determine the twisting pattern of 2,2'-bipyridyl compounds. The dyad shows crystallization-induced emission enhancement (CIEE).

Long-lived and oxygen-responsive photoluminescence in the solid state of copper(I) complexes bearing fluorinated diphosphine and bipyridine ligands.

Luminescence properties of a family of newly synthesized copper(i) complexes bearing 2,2'-bipyridine derivatives and 1,2-bis[bis(pentafluorophenyl)phosphino]ethane (dfppe), [Cu(diimine)(dfppe)]PF6, were investigated. The quantum yield and the lifetime of the emission of [Cu(6dmbpy)(dfppe)]PF6 (6dmbpy = 6,6'-dimethyl-2,2'-bipyridine) in the solid state under argon (Φ = 9%, τ = 16, 180 µs), which is one of the longest lifetimes among all copper(i) complexes bearing diimine and diphosphine, are much larger than those under air (Φ < 0.5%, τ = 1.5, 8.0 µs). Crystal packing, structural rearrangement in the excited state, and nature of the transitions are important for the photophysics of dfppe complexes. The voids in the crystals as well as the very long lifetimes of the excited states play a key role for oxygen responsive photoluminescence in the solid state.

Structures and photophysical properties of copper(I) complexes bearing diphenylphenanthroline and bis(diphenylphosphino)alkane: the effect of phenyl groups on the phenanthroline ligand.

A series of copper(I) complexes bearing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (dmpp) and a diphosphine ligand have been prepared. The diphosphine ligands used have two, three or four methylene carbons between the two phosphorus atoms. The crystallographic study has revealed that two of the three complexes have the mononuclear structure bearing dmpp and a bidentate diphosphine ligand, and one is a diphosphine-bridged binuclear complex. The photoluminescence of the complexes in solution was studied and compared with the previously reported complexes bearing 2,9-dimethyl-1,10-phenanthroline (dmp). It was found that the two phenyl groups on the phenanthroline ligand have a marked effect on the photophysical properties of the complexes; the intensity of the emission of the complexes is greatly enhanced by the phenyl groups. The photophysics of the complexes is discussed with the results of DFT and TDDFT calculations.

A single-molecular twin rotor: correlated motion of two pyrimidine rings coordinated to copper.

We describe the two correlated rotational motions of pyrimidine rings in 4,4'-dimethyl-2,2'-bipyrimidine ligated to Cu(i). The two pyrimidine rings delimited by anthryl and phenanthroline groups rotate to afford three isomers. (1)H NMR measurements revealed that the two rotational processes were activated at different temperatures. Cyclic voltammetry gave the kinetic and thermodynamic parameters that provide clear evidence of the correlation between the two rotational steps.

Highly emissive copper(I) complexes bearing diimine and bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane.

A highly emissive copper(I) complex bearing (4R,5R)-(-)-4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane (diop) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (dmpp), [Cu(dmpp)(diop)]PF6 (1·PF6), was newly synthesized. The quantum yield of the luminescence of 1·PF6 in degassed dichloromethane is 0.38, which is one of the highest values among all copper(I) complexes bearing two bidentate ligands, diimine and diphosphine, under the same conditions. The long lifetime (26 µs) and high intensity of the emission come from the small non-radiative decay rate of the excited states. The TD-DFT study indicates that the charge transfer transition from both copper and diphosphine to diimine orbitals plays an important role in the photophysical properties. Photophysics of [Cu(dmp)(diop)]PF6 (2·PF6, dmp = 2,9-dimethyl-1,10-phenanthroline) was also studied in order to reveal the effects of the introduction of the phenyl group at 4- and 7-positions of phenanthroline.

[µ-Butane-1,4-diylbis(di-phenyl-phos-phane)-κ(2) P:P']bis-{[butane-1,4-diylbis(di-phenyl-phosphane)-κ(2) P,P']copper(I)} bis-(hexa-fluorido-phosphate) diethyl ether disolvate.

In the centrosymmetric dinuclear copper(I) complex cation of the title compound, [Cu2(C28H28P2)3](PF6)2·2C4H10O, the Cu(I) atom is bonded to three P atoms of two butane-1,4-diylbis(di-phenyl-phosphane) (dppb) ligands with a triangular coordination geometry. One of these P atoms belongs to a bridging dppb ligand [Cu-P = 2.2381 (5) Å] and two belong to a chelating dppb ligand [Cu-P = 2.2450 (6) and 2.2628 (5) Å]. The bridging dppb ligand lies on an inversion centre. In the crystal, the cation and the PF6 (-) anion are linked by C-H⋯F inter-actions, forming a tape along [110]. The cation and the diethyl ether solvent mol-ecule are also linked by a C-H⋯O inter-action.

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 (1·BF4), and a dinuclear copper(I) complex, [(Cu(I))2(DPEPhos)2(µ-dmbmp)](BF4)2 [2·(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 1·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: 1·BF4 showed only isomers with either one (io isomer) or both (oo isomer) of the two methyl groups positioned away from the copper center, while dinuclear 2·(BF4)2 was only found as a symmetric (io-io) isomer, with each of the two methyl groups positioned toward different copper centers. The addition of [Cu(MeCN)2(DPEPhos)] (3·BF4) allowed both isomers of 1·BF4 to form 2·(BF4)2, although at different rates and via different pathways, which were analyzed using time-dependent UV-vis spectroscopy. The io isomer dinucleated more quickly than the oo isomer owing to it being able to form 2·(BF4)2 (i) without bond dissociation and (ii) without a sterically congested ii configuration around the copper center. In contrast, oo-1·BF4 required (i) recombination of the bipyrimidine coordination bonds or (ii) formation of a product with higher thermodynamic energy, unsymmetric (ii-oo) 2·(BF4)2. These findings are interpreted as demonstrating a novel kinetic property: a conversion rate determined by pyrimidine ring inversion.

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 (1·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 (2·BF4, MepmMepy = 4-methyl-2-(6'-methyl-2'-pyridyl)pyrimidine), Cu(Mepypm)(DPEphos)]BF4 (3·BF4, DPEphos = bis[2-(diphenylphosphino)phenyl]ether), [Cu(Mepypm)(L(Anth))]BF4 (4·BF4, L(Anth) = 2,9-bis(9-anthryl)-1,10-phenanthroline), and [Cu(Mepypm)(L(Macro))]BF4 (5·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.

Coordination programming of photofunctional molecules.

Our recent achievements relating to photofunctional molecules are addressed. Section 1 discloses a new concept of photoisomerization. Pyridylpyrimidine-copper complexes undergo a ring inversion that can be modulated by the redox state of the copper center. In combination with an intermolecular photoelectron transfer (PET) initiated by the metal-to-ligand charge transfer (MLCT) transition of the Cu(I) state, we realize photonic regulation of the ring inversion. Section 2 reports on the first examples of heteroleptic bis(dipyrrinato)zinc(II) complexes. Conventional homoleptic bis(dipyrrinato)zinc(II) complexes suffered from low fluorescence quantum yields, whereas the heteroleptic ones feature bright fluorescence even in polar solvents. Section 3 describes our new findings on Pechmann dye, which was first synthesized in 1882. New synthetic procedures for Pechmann dye using dimethyl bis(arylethynyl)fumarate as a starting material gives rise to its new structural isomer. We also demonstrate potentiality of a donor-acceptor-donor type of Pechmann dye in organic electronics.

Stimuli-responsive pyrimidine ring rotation in copper complexes for switching their physical properties.

This paper summarizes the results of our recent studies on the development of an artificial molecular rotor system that exhibits a change in redox potential and photoluminescence in response to external stimuli such as heat and photons. The molecular rotor is made of copper complexes bearing two bidentate ligands; the rotor is described here as [Cu(Rpmpy)(L(x))](+), where Rpmpy and L(x) are a 4-methyl-2-(2'-pyridyl)pyrimidine derivative and a bidendate ligand with bulky moieties, x, respectively, and the pyrimidine ring can rotate beside the copper centre while maintaining the pyridine-copper connection. The simplicity of the system enabled us to design the rotating motion more accurately. We expected that placing a wall in the rotational trajectory in the L(x) moiety would decrease the rate of the rotational dynamics. This slow rate of rotation was a key factor in achieving an external-stimuli-induced switching from thr equilibrium to metastable states. This switching was based on four stable isomers derived from the rotation and oxidation states, the behaviours of which were characterized for isolated copper(I) complexes using spectroscopic and electrochemical measurements at several temperatures. The steric shifts arising from the ring rotation were exploited not only to exhibit well-established oxidation-triggered motion but also to modulate the rest potential of the electrode, to manipulate the intramolecular electron transfer, to develop a redox potential switch based on photo-driven rotation, and to demonstrate the dual-luminescence behaviour.

Solvated-ion-pairing-sensitive molecular bistability based on copper(I)-coordinated pyrimidine ring rotation.

We describe herein the effect of solvated ion pairing on the molecular motion of a pyrimidine ring coordinated on a copper center. We synthesized a series of heteroleptic copper(I) complex salts bearing an unsymmetrically substituted pyridylpyrimidine and a bulky diphosphine. Two rotational isomers of the complexes were found to coexist and interconvert in solution via intramolecular ligating atom exchange of the pyrimidine ring, where the notation of the inner (i-) and outer (o-) isomers describes the orientation of the pyrimidine ring relative to the copper center. The stability of the pyrimidine orientation was solvent- and counterion-sensitive in both 2·BF(4) {2(+) = [Cu(Mepypm)(dppp)](+), where Mepypm = 4-methyl-2-(2'-pyridyl)pyrimidine and dppp = 1,3-bis(diphenylphosphino)propane} and previously reported 1·BF(4), which possesses a bulky diphosphine ligand (1(+) = [Cu(Mepypm)(DPEphos)](+), where DPEphos = bis[2-(diphenylphosphino)phenyl] ether). Two rotational isomers of 2(+) were separately obtained as single crystals, and the structure of each isomer was examined in detail. Both the enthalpy and entropy values for the rotation of 2·BF(4) in CDCl(3) (ΔH = 6 kJ mol(-1); ΔS = 25 J K(-1) mol(-1)) were more positive than that tested under other conditions, such as in more polar solvents CD(2)Cl(2), acetone-d(6), and CD(3)CN. The reduced contact of the anion to the cation in a polar solvent seems to contribute to the enthalpy, entropy, and Gibbs free energy for rotational isomerization. This speculation based on solvated ion pairing was further confirmed by considering the rotational behavior of 2(+) with a bulky counterion, such as B(C(6)F(5))(4)(-). The findings are valuable for the design of molecular mechanical units that can be readily tuned via weak electrostatic interactions.

Synthesis of optically active tertiary silanes via Pd-catalyzed enantioselective arylation of secondary silanes.

We herein describe the development of an efficient enantioselective catalytic system that promotes the arylation of secondary silanes. Our method involves treatment of secondary silanes and aryl iodides with a Pd(2)(dba)(3)-asymmetric phosphoramidite ligand system to afford optically active tertiary silanes with good enantioselectivities.