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New octahedral rhenium cluster complexes [{Re6Q8}(SO3)6]10- (Q = S or Se) were synthesized starting from [{Re6Q8}(H2O)4(OH)2]·12H2O. The complexes were crystallized as sodium salts and characterized by X-ray single-crystal diffraction and elemental analyses, IR, UV/vis and luminescence spectroscopies. Magnetic relaxation data demonstrate the complex formation of the cluster units with gadolinium ions. The analysis of the magnetic relaxation rates measured at various Gd:cluster ratios and different concentrations revealed the conversion of the aggregates (Gdx[{Re6Se8}(SO3)6]y)n- into a nanoparticulate form even at x = 1 and y ≥ 1. Thus, the self-assembly of the cluster units into the nanoparticles is greatly facilitated by counterion binding with sodium cations. The concentration conditions were optimized for the formation and hydrophilization of NaxGdy[{Re6Q8}(SO3)6]-based colloids with the magnetic relaxivity values of r1(2) = 21.0(24.1) and r1(2) = 25.9(29.8) mM-1 s-1 for the {Re6S8}2+ and {Re6Se8}2+ derivatives, respectively.

Luminescent silver(I) halogenido coordination polymers [Ag2X2(PPh3)2(bpy)] n (X = I, Br, Cl) have been prepared. The iodido and bromido complexes exhibit strong blue phosphorescence assignable to the 3π-π*-excited-state of bpy, whereas the chlorido complex shows luminescence thermochromism due to the π-π*-state of bpy and charge transfer from the {Ag2Cl2} core to the bpy π*-orbital. Taking advantage of their structural similarities, we prepared a series of mixed-halogenido silver(I) complexes [Ag2(X xX'(1- x))2(PPh3)2(bpy)] n (X, X' = I, Br, Cl) at varying molar fractions as solid solutions. The mixed-halogenido complexes are as strongly luminescent as their parent complexes. The detailed study of their structure and emissive properties revealed smooth energy migration between the luminescent units and modification of the luminescence properties based on the planarity of bpy.

Reactions of [{Re6Q8}Br6]4−/3− (Q = S, Se) with molten imidazole lead to the formation of two new neutral cluster complexes [{Re6Q8}(imzH)4(imz)2] (imzH = imidazole). The interaction of [{Re6Q8}(imzH)4(imz)2] with hydrohalic acids resulted in cationic complexes [{Re6Q8}(imzH)6]X2 (X = Cl, Br). All compounds were characterised by X-ray single-crystal and powder diffraction analyses, elemental analysis, energy dispersive X-ray and IR spectroscopies. The luminescence of the neutral compounds [{Re6Q8}(imzH)4(imz)2] was also studied.

We report the emission properties of the octahedral hexamolybdenum(II) bromide-core ({Mo6Br8}4+) clusters having a series of terminal aromatic carboxylate ligands (RCOO), [{Mo6Br8}(RCOO)6]2–, in solution and crystalline phases. The acid dissociation constant of RCOOH (pKa(L)) was shown to govern the redox and emission properties of the clusters. Temperature (T)-controlled emission experiments (3–300 K) demonstrated that the clusters showed large T-dependent emission energies (νem) and lifetimes (τem) because of zero-magnetic-field splitting in the emissive excited triplet (T1) states. The spin sublevel (Φn, n = 1–4) model in the T1 state of the cluster explained very well the T-dependent emission characteristics (νem and τem), irrespective of the clusters studied. Furthermore, we revealed that the energy difference between the lowest-energy (Φ1) and energetically upper-lying third (Φ3) or fourth spin sublevels (Φ4), ΔE13 or ΔE14, respectively, correlated very well with pKa(L). The results are discussed ...

We report temperature (T = +22.5 ∼ -57.0 °C)-controlled optical trapping of single dimethylsulfoxide (DMSO) droplets with the diameter (d) of 7-15 μm in air. Optically levitated DMSO microdroplets containing 0.1 mol/dm3 (=M) potassium iodide (KI) as an additive for reducing the vapor pressure of DMSO in air have been suggested to take supercooled liquid states even below the freezing temperature (fp) of the bulk DMSO liquid (fp = +18.4 °C in the presence of 0.1 M KI) as seen in bright-field microscopic observations of the droplet. Clear evidence for supercooling of an aerosol DMSO microdroplet below fp has been obtained by in situ optical trapping-polarized Raman microspectroscopy of the droplet down to -14.9 °C. Analysis of the polarized Raman spectral data of an aerosol DMSO droplet (d = ∼10 μm) has demonstrated that the droplet at +22.5, +0.2, or -14.9 °C is characterized by the rotational relaxation time (τrot) of a DMSO molecule in the droplet being 1.95, 2.58, or 3.90 ps, respectively. On the basis of the τrot values and the Stokes-Einstein equation (τrot = 8πa3η/kBT where a, η, kB are the radius (1.883 A) of a DMSO molecule, the viscosity in DMSO, and the Boltzmann constant, respectively), the η values in the DMSO microdroplet in air at +22.5, +0.2, or -14.9 °C have been estimated to be 2.39, 2.94, or 4.20 cP, respectively, while that of bulk DMSO liquid at +20.5 °C is 1.98 cP. We also report the T-dependence (+22.5 > T > -14.9 °C) of the viscosity in a single aerosol DMSO microdroplet (d = ∼10 μm) and the effects of aerosolization in air on the viscosity in DMSO.

Tricyanidonitridorhenium(V) complexes with 2,2'-bipyridine (bpy) derivatives in which the 4 and 4' positions were substituted by X, [ReN(CN)3(X2bpy)]- (X = NMe2, NH2, OMe, Me, Cl, and Br), were newly synthesized and characterized. The structures of the new complexes were determined by single-crystal X-ray analysis. UV-vis spectra of the complexes in dimethyl sulfoxide (DMSO) showed that the peak maximum wavelengths of rhenium-to-π* bpy-type-ligand charge transfer were in the range of 474-542 nm. Cyclic voltammograms in n-(C4H9)4NPF6-DMSO showed one-electron oxidation and reduction waves corresponding to the Re(VI/V) and X2bpy0/- processes, respectively. The new complexes and [ReN(CN)3bpy]- showed photoluminescence in the crystalline phase at 295 and 80 K and in DMSO at 295 K. The origin of the emission in DMSO was attributed to the triplet nature of the rhenium-to-π* bpy-type-ligand charge-transfer transition. Density functional theory calculations showed that the highest occupied and lowest unoccupied molecular orbitals were primarily localized on the dxy orbital of the rhenium and π* orbitals of the bpy-type ligand, respectively.

The temperature (T) dependences of the emissions from the tetra-n-butylammonium salts of [{Mo6X8}Y6]2– (X, Y = Cl, Br, and I) in optically transparent polyethylene glycol dimethacrylate matrixes were studied in the T range of 3–300 K. [{Mo6Cl8}Y6]2–, [{Mo6Br8}Y6]2–, and [{Mo6I8}I6]2– showed the T-dependent emission characteristics similar to those of other hexanuclear Mo(II), Re(III), and W(II) clusters reported previously, while [{Mo6I8}Br6]2– and [{Mo6I8}Cl6]2– exhibited the emission properties different from those of other [{Mo6X8}Y6]2– clusters. The photophysical behavior of these clusters was explained by the excited triplet state spin-sublevel (Φn, n = 1–4) model irrespective of the nature of X and Y. The zero-magnetic-field splitting energies between the lowest energy (Φ1) and the higher energy spin sublevels (Φ4 or Φ3) caused by the first- or second-order spin–orbit coupling, ΔE14 or ΔE13, were evaluated to be 620–870 or 50–99 cm–1, respectively. We found the linear correlation between the ΔE14 or...

Novel heteroleptic arylborane–ruthenium(II) complexes having a series of ancillary ligands L′ ([Ru(B2bpy)L′2]2+) in CH3CN showed low-energy/intense metal-to-ligand charge transfer (MLCT)-type absorption and intense/long-lived emission compared to the reference complexes. The spectroscopic and photophysical properties of [Ru(B2bpy)L′2]2+ were shown to be manipulated synthetically by the electron-donating ability of the ancillary ligand(s). The intense and long-lived emission observed for [Ru(B2bpy)L′2]2+ in CH3CN at 298 K is responsible for the accelerated radiative and decelerated nonradiative decay processes, which are controllable through the electronic structures of the ancillary ligand(s). On the basis of the present systematic study, furthermore, we succeeded in demonstrating the Strickler–Berg-type relation between the molar absorption coefficients of the MLCT bands and the radiative rate constants of the complexes.

Photoactive transition metal compounds that are prone to reversible redox reactions are important for myriad applications, including catalysis, optoelectronics, and sensing. This article describes chemical and electrochemical methods to prepare cluster complex (Bu4N)[{Mo6I8}Cl6], a rare example of a 23 e- cluster complex within the family of octahedral clusters of Mo, W, and Re. The low temperature and room temperature crystal structures; electronic structure; and the magnetic, optical, and electrochemical properties of this complex are described.

Reactions of new heterocyclic ligands 2-(pyridin-2-yl)-[1,2,4]triazolo[1,5-a]quinolin-9-ol (L-OH), 2-(pyridin-2-yl)-[1,2,4]triazolo[1,5-a][1,10]phenanthroline (L-Py) and 2-methyl-[1,2,4]triazolo[1,5-a][1,10]phenanthroline (L-Me) with [Re(CO)5Br] in toluene afforded the complexes of the general formula [(L)Re(CO)3Br]. Substitution of the Br− ligand in [(L)Re(CO)3Br] by C3F7COO− leads to [(L)Re(CO)3(OOCC3F7)] and results in increased emission lifetime.

Temperature (T)-dependent emission from [{Mo6X8}(n-C3F7COO)6]2– (X = Cl (1), Br (2), and I (3)) in optically transparent polyethyleneglycol dimethacrylate matrices were studied in 3 K < T < 300 K to elucidate the spectroscopic and photophysical properties of the clusters, in special reference to zero-magnetic-field splitting (zfs) in the lowest-energy excited triplet states (T1) of the clusters. The cluster complexes 1 and 2 showed the T-dependent emission characteristics similar to those of [{Mo6Cl8}Cl6]2–, while 3 exhibited emission properties different completely from those of 1 and 2. Such T-dependent emission characteristics of 1, 2, and 3 were explained successfully by the excited triplet state spin-sublevel (Φn, n = 1 – 4) model. The zfs energies between the lowest- (Φ1) and highest-energy spin-sublevels (Φ4), ΔE14, resulted by the first-order spin-orbit coupling, were evaluated to be 650, 720, and 1000 cm–1 for 1, 2, and 3, respectively. The emission spectra of 1, 2, and 3 in CH3CN at 298 K were r...

A novel sensor, 4-[2-(9-anthryl)ethynyl]-1,10-phenanthroline (1), exhibits highly intense fluorescent in the wavelength region of 440-600 nm (maximum wavelength (λf) = 470 nm) with the quantum yield (Φf) and lifetime (τf) being 0.90 and 4.2 ns, respectively, in CH3CN at 298 K. In the presence of a divalent cation (M2+ = Ba2+, Ca2+, Mg2+, or Zn2+) in CH3CN, sensor 1 can tightly bind M2+ and shows intense fluorescent (Φf = 0.90-0.19, τf = 2.1-6.9 ns) with the color being dependent on the nature of M2+ (λf = 514-584 nm). The results demonstrate that a single fluorescent sensor 1 is capable of simultaneous identification and quantitation of M2+ based on λf and the fluorescent intensity (Φf), respectively. The fluorescence maximum energy of the [1-M2+] complex is shown to correlate linearly with the pKa value of M2+. The spectroscopic and photophysical properties of sensor 1 in the absence and presence of M2+ are also discussed.

The reactions between the tetra-n-butylammonium salt of [{Mo6I8}I6](2-) and silver carboxylates RCOOAg (R = CH3 (1), C(CH3)3 (2), α-C4H3O (3), C6H5 (4), α-C10H7 (5), or C2F5 (6)) in CH2Cl2 afforded new carboxylate complexes [{Mo6I8}(RCOO)6](2-). The complexes were characterized by X-ray single-crystal diffraction and elemental analysis, cyclic/differential pulse voltammetry, and IR, NMR, and UV-visible spectroscopies. The emission properties of the complexes 1-6, and those of the earlier reported complexes with R = CF3 (7) and n-C3F7 (8), were studied both in acetonitrile solution and in the solid state. In deaerated CH3CN at 298 K, all of the complexes 1-8 exhibit intense and long-lived emission with the quantum yield and lifetime being 0.48-0.73 and 283-359 μs, respectively. The oxidation (Eox)/reduction (Ered) potentials of the complexes correlate linearly with the pKa value of the terminal carboxylate ligands L = RCOO (pKa(L)). Reflecting the pKa(L) dependences of Eox/Ered, the emission energy (νem) of the complexes was also shown to correlate with pKa(L). The present study successfully demonstrates synthetic tuning of the redox, spectroscopic, and photophysical characteristics of a {Mo6I8}(4+)-based cluster complex with pKa(L).

Thiolato-bridged dinuclear, tetranuclear, and hexanuclear Cu(I) complexes [Cu2(P∧S)2(PPh3)2], [Cu4(P∧S)4(CH3CN)2], and [Cu6(P∧S)6] (abbreviated as Cu2, Cu4, and Cu6, respectively, P∧S = 2-(diphenylphosphino)benzenethiolate, PPh3 = triphenylphosphine) were synthesized and characterized by elemental analyses and single-crystal X-ray diffraction measurements. These complexes had {Cu2S2}, {Cu4S4}, and {Cu6S6} cluster cores and exhibited strong luminescence at room temperature in solid states. Different luminescence properties were observed depending on the core structure. Cu2, Cu4, and Cu6 exhibited blue-green (λmax = 482 nm, Φem = 0.52), green (λmax = 526 nm, Φem = 0.19), and yellow (λmax = 553 nm, Φem = 0.49) luminescence, respectively, at 298 K in the solid state; among them, only Cu6 showed luminescence thermochromism. Different radiative rate constants at room temperature and 78 K derived from the emission lifetimes and quantum yields indicate that the luminescence from Cu2 and Cu4 at room temperature or...

Neutral halogenido copper(I) units {CunXn} are widely found in the luminescent copper(I) complexes. In this review, we describe the luminescent properties of complexes with the halogenido-bridged dimeric core, {Cu2(μ-X)2}, which is one of the basic structural motifs of {CunXn}, as well as their synthetic methods and structural features. The available emissive excited states and their approximate energies are discussed by comparing the emission energies among the complexes with different ligand combinations. The trend of the quantum yields in the {Cu2X2} complexes will also be discussed.

Octahedral rhenium cluster complexes with organic apical ligands have a high potential to be used in different fields due to their intrinsic luminescence and X-ray contrast properties. A series of new compounds based on cations [{Re6Q8}(3-Me-pzH)6]2+, where Q is S or Se and 3-Me-pzH is 3-methylpyrazole, were obtained and characterized in the solid state (FTIR, elemental and single crystal diffraction analysis) and in solution (1H NMR and ESI-MS). The compounds possess luminescence properties that mainly depend on inner Q ligands indicating the {Re6Q8}2+ core-centered nature of emission.

Interaction of cluster anions [{Re6Q8}X6]4−/3− (Q = S or Se; X = Cl, Br or I) with molten pro-ligands – pyrazole (pzH) and 3,5-dimethylpyrazole (3,5-Me2pzH) has led to the formation of cationic apically homoleptic cluster complexes [{Re6Q8}L6]2+ (L = pzH or 3,5-Me2pzH). All new compounds were characterized by a set of physicochemical properties such as X-ray diffraction analyses on crystals and powders, FTIR and NMR spectroscopies. Synthesis of the complete series of pyrazole complexes and finishing the earlier series of 3,5-dimethylpyrazole complexes with different halogens in addition to the previously described [{Re6Q8}(3,5-Me2pzH)6]Br2·2(3,5-Me2pzH) (Q = S, Se) allowed us to study dependence of luminescence properties on the nature of the inner or outer ligands as well as counterions in detail.

The hexarhenium cluster complexes with benzotriazolate apical ligands [{Re6(μ3-Q)8}(BTA)6](4-) (Q = S, Se; BTA = benzotriazolate ion) were obtained by the reaction of [{Re6(μ3-Q)8}(OH)6](4-) with molten 1H-BTA (1H-benzotriazole). The clusters were crystallized as potassium salts and characterized by X-ray single-crystal diffraction, elemental analyses, and UV-vis and luminescence spectroscopy. In addition, their cellular uptake and toxicity were evaluated. It was found that both clusters exhibited luminescence with high lifetimes and quantum yield values; they were taken up by the cells illuminating them under UV irradiation and, at the same time, did not exhibit acute cytotoxic effects.

This work is devoted to the preparation of trans-[Re6S8(CN)4(OH)(H2O)]3− and trans-[Re6S8(CN)4(H2O)2]2− cluster complexes starting from trans-[Re6S8(CN)4(OH)2]4− and a study of their luminescence properties. The controlled separation of each species could be achieved by pH adjustment: pH > 10, 5.5 H 3 O 2 - intercluster bridging groups through strong hydrogen bonding. The trans disposition of the H 3 O 2 - groups around Re6 enables the formation of polymeric linear chains of cluster complexes.

The reaction of [Mo6I14]2– with methyl propiolate HC≡CC(O)OMe in the presence of Ag+ and Et3N yielded the new luminescent complex [Mo6I8(C≡CC(O)OMe)6]2–, the first fully organometallic complex in the family of octahedral {M6X8} clusters. The cluster was crystallized as tetraphenylphosphonium salt and characterized by X-ray single-crystal diffraction and elemental analyses, mass spectrometry, 13C NMR, UV–vis, and luminescence spectroscopies.

We demonstrate the efficient trapping of myoglobin (Mb), which is a small protein, in aqueous solution using a 1064 nm laser beam. Conventional optical tweezers exert barely sufficient radiation force (RF) on nanometer-sized dielectric objects, such as small proteins and organic molecules, for manipulation of them. One possible candidate to enhance the RF is to use laser light with a wavelength that is electronically resonant with the electronic transition of the target object: resonant optical trapping (ROT). The near-infrared absorbance dependence of ROT of Mb and optical trapping of Mb without the heme cofactor (apomyoglobin) clearly indicates that the heme cofactor plays a crucial role in the ROT of Mb. Furthermore, confocal Raman microspectroscopy suggested the structural conformational change of trapped Mb. Such an ROT technique would open up new channels in the development of nanobioscience, such as transportation/crystallization techniques and a selective molecular sorting technique for biomolecules.

We discovered for aqueous thermoresponsive polymer solutions that only a slight change in stereoregularity of the polymer can drastically accelerate phase separation. Single molecule fluorescence tracking (SMT) for an isotactic-slight-rich (meso-diad-rich) polymer sample solution revealed an interpolymer nanonetwork even before phase separation, and also revealed a novel phase in which translational molecular motion was frozen after phase separation. For such systems, fluorescence correlation spectroscopy (FCS) provided quantitative information on molecular diffusion. The results on FCS well agreed with the interpolymer nanonetwork model that was proposed on the basis of SMT measurement. We demonstrate such a novel method to control phase separation dynamics and also the interpolymer nanonetwork model.

Fluorescence correlation spectroscopy was applied to the measurement of local temperature in the vicinity of gold nanoparticles adsorbed on the surface of glass substrate under the photoexcitation at a wavelength of 633 nm. From the diffusion coefficient of fluorescent guest dyes and the temperature dependence of the viscosity of a solution, the increase in the temperature was estimated. It was revealed that the temperature ca. 5 μm from the gold nanoparticles linearly increased with an increase in the incident laser power and an increase in the number of gold nanoparticles on the substrates. Temperature elevation coefficients of single gold nanoparticles with 100 and 150 nm diameters under the irradiation at 633 nm were, respectively, estimated to be (2.3 and 6.9) × 10–3 K·kW–1·cm2. These values could be interpreted on the basis of the absorption coefficients of gold nanoparticles and the thermal conduction in the solution.

Six-coordinate distorted octahedral tetracyanidonitridorhenium(V) and -technetium(V) complexes with a volatile organic compound (VOC) coordinating at the trans position of a nitrido ligand, (PPh4)2[MN(CN)4L] (M = Re, L = MeOH, EtOH, acetone, or MeCN; M = Tc, L = MeOH), and five-coordinate square-pyramidal tetracyanidonitrido complexes without an axial ligand, (PPh4)2[MN(CN)4] (M = Re or Tc), were synthesized and characterized. Single-crystal X-ray structural analysis was carried out for (PPh4)2[MN(CN)4L] (M = Re, L = MeOH, EtOH, or acetone; M = Tc, L = MeOH) and (PPh4)2[ReN(CN)4]. All complexes studied showed photoluminescence in the solid state at room temperature. Reversible luminescence switching between six- and five-coordinate rhenium(V) complexes and between the relevant six-coordinate rhenium(V) complexes except that between the MeCN and acetone complexes was achieved by exposing them to VOC vapor in the solid state at room temperature. Luminescence changes were observed from the five-coordinate technetium(V) complexes in a MeOH vapor atmosphere in the solid state. In contrast, no vapochromic luminescence was observed from the five- and six-coordinate complexes in an acetone vapor atmosphere.

We report for the first time quasi-one-step six-electron electrochemical reduction of a new hexanuclear molybdenum(II) bromide cluster having terminal 3,5-dinitrobenzoate ligands: [Mo6Br8(DNBA)6]2–. The electrochemical responses of the cluster were studied based on cyclic (CV), differential pulse, and normal pulse voltammetries, together with the analytical simulations of the CV and spectroelectrochemistry. CV simulations have revealed that the electrochemical reaction of the cluster proceeds in an EEEEEE scheme, and the potential differences between the two adjacent reduction steps are in the range of 15–30 mV. These potential differences indicate quite smooth and quasi-one-step six-electron reduction of the cluster.

The dynamic and static phase separation behavior in aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions is highly sensitive to the tacticity of PNIPAM. We investigated the phase separation dynamics of aqueous solutions of PNIPAM with different tacticities (atactic and syndiotactic-rich types) and found that the phase separation dynamics of syndiotactic-rich PNIPAM was much different from that of atactic-type PNIPAM. First, phase separation in syndiotactic-rich PNIPAM was faster. Second, there was a critical point (Ccp) in the concentration dependence of the phase separation rate: the phase separation accelerated dramatically when the solution concentration was higher than 2.0 wt % (= Ccp). Third, syndiotactic-rich PNIPAM required a higher thermal energy for phase separation compared to atactic PNIPAM. Such behavior can be explained on the basis of the high hydrophobicity of syndiotactic-rich PNIPAM in a dehydrated state and a diffusion-controlled aggregation model. The present study shows that precise control of the stereoregularity will open new channels toward the design and development of stimuli-responsive-polymer-based smart materials.

Nanostructure-enhanced optical trapping of polymer beads was investigated by means of fluorescence microspectroscopy. It was found that trapping behavior was quite sensitive to the particle size as well as excitation light intensity. We present a 2D closely packed assembly of polystyrene nanospheres on a gold nanostructure that is triggered by gap-mode localized surface plasmon (LSP) excitation. We discuss the trapping mechanism from the viewpoints of not only the radiation force but also of the thermal force (thermophoresis and thermal convection) induced by near-infrared laser irradiation. Thermophoresis worked as a repulsive force whose direction was opposed to that of the radiation force. On the other hand, thermal convection acted in favor of trapping: It supplied nanospheres toward the LSP excitation area. By suppressing the repulsive force, the assembled trapped nanospheres took the form of hexagonal shapes on a gold nanostructure. By optimizing irradiation parameters, we achieved 2D manipulation o...

The dynamics of thermoresponsive phase-separation processes in aqueous poly(N-isopropylacrylamide) (PNIPAM) was studied using a laser temperature-jump technique combined with photometry. The time constant for phase separation (τ) was determined with high accuracy for various molecular weights (Mw) and concentrations (C) of PNIPAM in solution. For the C-dependence, τ decreased with increasing concentration, and eventually converged to a constant value (≈ 50 ms) at high concentration. Such behavior can be interpreted in terms of inter-polymer-chain entanglement and diffusion prior to phase separation. On the other hand, there was an optimum value of Mw at which the phase separation was fastest. The origins of these experimental results are discussed within the framework of a diffusion-controlled model.

Heteropolynuclear Pt(II) complexes with 3,5-diphenylpyrazolate [Pt(2)Ag(4)(μ-Cl)(2)(μ-Ph(2)pz)(6)] (3), [Pt(2)Ag(2)Cl(2)(μ-Ph(2)pz)(4)(Ph(2)pzH)(2)] (4), [Pt(2)Cu(2)Cl(2)(μ-Ph(2)pz)(4)(Ph(2)pzH)(2)] (5), [Pt(2)Ag(4)(μ-Cl)(μ-Me(2)pz)(μ-Ph(2)pz)(6)] (7), and [Pt(2)Ag(4)(μ-Me(2)pz)(2)(μ-Ph(2)pz)(6)] (8) have been prepared and structurally characterized. These complexes are luminescent except for 5 in the solid state at an ambient temperature with emissions of red-orange (3), orange (4), yellow-orange (7), and green (8) light, respectively. Systematic red shift of the emission energies with the number of chloride ligands was observed for 3, 7, and 8. DFT calculations indicate that the highest occupied molecular orbital (HOMO) as well as HOMO-1 of the heterohexanuclear complexes, 3, 7, and 8, having Pt(2)Ag(4) core, mainly consist of dδ orbital of Pt(II) and π orbitals of Ph(2)pz ligands, while the lowest unoccupied molecular orbital (LUMO) of these complexes mainly consists of in-phase combination of 6p of two Pt(II) centers and 5p of four Ag(I) centers. It is likely that the emissions of 3, 7, and 8 are attributed to emissive states derived from the Pt(2)(d)/π → Pt(2)Ag(4) transitions, the emission energy of which depends on the ratio of chloride ligands to pyrazolate ligands.

Optical trapping of flexible polymer chains to a metallic nanostructured surface was explored by microscopic imaging and confocal fluorescence spectroscopy. A fluorescence-labeled poly(N-isopropylacrylamide) was targeted, being a representative thermo-responsive polymer. Upon resonant plasmonic excitation, it was clearly observed that polymers were assembled into the excitation area to form molecular assemblies. Simultaneously, fluorescence from the area was obviously intensified, indicating an increase in the number of polymer chains at the area. The excitation threshold of light intensity that was required for obvious trapping was 1 kW/cm2, which was much lower by a factor of 104 than that for conventional trapping using a focused laser beam. The morphology of the assemblies was sensitive to excitation intensity. We precisely evaluated temperature rise (ΔT) around the metallic nanostructure upon plasmonic excitation: ΔT ≈ 10 K at 1 kW/cm2 excitation. This temperature rise was an origin of a repulsive fo...

Poly[(2-ethoxy) ethoxy ethyl vinyl ether] (poly(EOEOVE)) is a representative thermoresponsive polymer in aqueous solution for which the time constants of the phase separation (PS) are determined with high accuracy. It is revealed that the PS dynamics of the polymer are entirely different from those of the poly(N-isopropylacrylamide) (PNIPAM) system, which is an alternative representative thermoresponsive polymer. Poly(EOEOVE) exhibits complicated PS behavior that is described using double exponential functions. The PS of poly(EOEOVE) is much faster than the PS of PNIPAM in aqueous solutions and becomes faster with increasing concentration of the polymer. PS behavior that is particular to the present system is successfully understood within the framework of the aggregation mechanism.

A hexarhenium cyanohydroxo anionic cluster complex [Re6Se8(CN)4(OH)2]4− was synthesized for the first time starting from [Re6Se8(OH)6]4−, which was crystallized as a salt of the composition Cs2.75K1.25[Re6Se8(CN)4(OH)2]·H2O (1). The reaction of the complex with Cu2+ in an aqueous ammonia or methylamine solutions afforded [Cu(NH3)5]2[Re6Se8(CN)4(OH)2]·8H2O (2) or [{Cu(CH3NH2)4}2Re6Se8(CN)4(OH)2] (3), respectively. All of these three compounds were characterized by a single-crystal X-ray diffraction method. Compound 1 is crystallized in the tetragonal space group I4/m with eight formula units per cell (a = b = 17.4823(14) A, c = 19.430(2) A, V = 5938.3(10) A3); compound 2 is crystallized in the monoclinic space group P21/n with two formula units per cell (a = 12.1845(13) A, b = 8.6554(9) A, c = 19.2568(19) A, β = 91.081(2)°, V = 2030.5(4) A3); compound 3 is crystallized in the orthorhombic space group Cmcm with four formula units per cell (a = 19.816(4) A, b = 14.611(3) A, c = 13.751(3) A, V = 3981.2(13) A3). The luminescence properties of 1 were studied in both aqueous solution and solid state. In addition, the electronic structure of [Re6Se8(CN)4(OH)2]4− was elucidated by DFT calculations.

The freezing processes of single micrometer-sized aqueous ammonium sulfate droplets levitated in air were observed by means of laser trapping and spectroscopy techniques. Single micrometer-sized aqueous ammonium sulfate droplets were levitated by radiation pressure in air. When a levitated droplet was cooled below 213 K, a supercooled droplet was turned from the liquid to solid state. To the best of our knowledge, this is the first observation of the freezing processes of single micrometer-sized supercooled aqueous solution droplets in air by means of laser trapping and spectroscopy techniques.

We report the redox, absorption, and emission characteristics of the tris(1,10-phenanthroline)ruthenium(II) complexes [Ru(phen)(3)](2+) bearing a (dimesityl)boryldurylethynyl (DBDE) charge-transfer (CT) unit at the 4 (4BRu(2+)) or 5 (5BRu(2+)) position of one of the three phen ligands. In acetonitrile at 298 K, 4BRu(2+) showed absorption and emission maximum wavelengths at 473 and 681 nm, respectively, which were shifted to longer wavelengths by 25 and 74 nm, respectively, compared with the relevant value of 5BRu(2+), 448 and 607 nm, respectively. The effects of a fluoride ion on the absorption and emission spectra of the complexes demonstrated that the CT interaction between the π-electron system in the phen ligand (π(aryl)) and the vacant p orbital on the boron atom (p(B)) in the DBDE group (i.e., π(aryl)-p(B) CT) participated in the excited states of the complexes in addition to the Ru(II)-to-phen metal-to-ligand CT (MLCT) interaction. Reflecting such synergistic MLCT/π(aryl)-p(B) CT, both 4BRu(2+) and 5BRu(2+) exhibited intense emission at 298 K with a quantum yield of 0.11. Furthermore, the emission lifetime of 4BRu(2+) was as long as 12 μs and almost independent of the temperature (T = 280-330 K). The present study indicated that the nonemissive dd excited triplet state did not participate to nonradiative decay in the MLCT excited triplet state of 4BRu(2+). The effects of the synergistic MLCT/π(aryl)-p(B) CT interactions on the redox, absorption/emission, and photophysical characteristics of 4BRu(2+) and 5BRu(2+) are discussed in detail.

A room-temperature reaction between [Re 6 S 8 (OH) 6 ] 4− and acetic acid in an aqueous solution resulted in the substitution of all terminal hydroxo groups by acetate ligands, affording a new hexanuclear anionic rhenium cluster complex [Re 6 S 8 (CH 3 COO) 6 ] 4− . The complex was isolated as a potassium salt with the composition of K 4 [Re 6 S 8 (CH 3 COO) 6 ]·8H 2 O ( 1 ) and characterized by X-ray single-crystal diffraction and elemental analyses, IR, 1 H NMR, UV–Vis, and luminescence spectroscopies.

One of the recent hot topics in the fields of plasmonics and related nanophotonics is optical trapping of nano/microparticles based on surface plasmon. Experimental demonstration of such trapping by gap-mode plasmon has hitherto been limited so far to a few reports in which submicrometer polymer beads were trapped with intense irradiation at MW/cm2, satisfying an energetic condition of U > kT. (U is the potential energy of the trap and kT is an averaged thermal background energy.) We demonstrate plasmon-based optical trapping of a luminescent quantum dot (Q dot, diameter ≥10 nm) with a very weak irradiation (0.5−10 kW/cm2). The most important discovery is that the Q dot trapping was clearly observed through luminescence detection even under an energetic condition of U < kT, on the basis of which we propose a novel concept that is peculiar to plasmon-based trapping at a nanogap.

In this paper, we demonstrated that the photon forces that are generated by a near-infrared (1064 nm) focused laser beam can manipulate (optically trap) small amino acid molecules in aqueous solutions. Under observation with an optical microscope, we observed the gradual growth of a particle-like assembly of objects at the focal point during laser irradiation into an aqueous arginine solution. The observation was a molecular assembly of arginine by means of confocal Raman microspectroscopy. Such molecular assemblies were also observed for other amino acids (glycine, proline, serine, and alanine), showing that the optical manipulation technique can be extensively applied to the micromanipulation of amino acids. From experimental observations and numeral calculations, we consider that the origin of the present manipulation phenomenon is ascribed to optical trapping, not of individual molecules, but of molecular clusters of amino acids.

New sulfide-capped octahedral hexarhenium(III) complexes containing 4-phenylpyridine (ppy) or 1,2-bis(4-pyridyl)ethane (bpe) ((n-C(4)H(9))(4)N)[mer-{Re(6)S(8)Cl(3)(ppy)(3)}] ((Bu(4)N)[1]), ((n-C(4)H(9))(4)N)(2)[trans-{Re(6)S(8)Cl(4)(ppy)(2)}] ((Bu(4)N)(2)[2a]), ((n-C(4)H(9))(4)N)(2)[cis-{Re(6)S(8)Cl(4)(ppy)(2)}] ((Bu(4)N)(2)[2b]), ((n-C(4)H(9))(4)N)(2)[trans-{Re(6)S(8)Cl(4)(bpe)(2)}] ((Bu(4)N)(2)[3a]), and ((n-C(4)H(9))(4)N)(2)[cis-{Re(6)S(8)Cl(4)(bpe)(2)}] ((Bu(4)N)(2)[3b]) were prepared, and X-ray single-crystal structure determination was carried out for (Bu(4)N)(2)[2a] and (Bu(4)N)(2)[3a]. The photophysical properties of these complexes were studied both in acetonitrile at 298 K and in the solid state at 298 and 80 K, along with those of the known 4,4'-bipyridine (bpy) analogues ((n-C(4)H(9))(4)N)[mer-{Re(6)S(8)Cl(3)(bpy)(3)}] ((Bu(4)N)[4]), ((n-C(4)H(9))(4)N)(2)[trans-{Re(6)S(8)Cl(4)(bpy)(2)}] ((Bu(4)N)(2)[5a]), and ((n-C(4)H(9))(4)N)(2)[cis-{Re(6)S(8)Cl(4)(bpy)(2)}] ((Bu(4)N)(2)[5b]). The photophysical data of [5a](2-) and [5b](2-) in solution and in the solid state were significantly different from those of other complexes. On the basis of experimental observations of [2a](2-) and [5a](2-) and density-functional theory (DFT) calculations, it was concluded that [5a](2-) and [5b](2-) exhibited metal (Re(6)S(8) core)-to-ligand (bpy) charge transfer (MLCT) type emission. This is the first unambiguous demonstration of MLCT type emissions for the hexarhenium complexes. The MLCT components, where present, are only minor in the case of the emissions of [1](-), [2a](2-), [2b](2-), and [4](-); these can be explained primarily as the contributions of the intracore electronic transitions. The emissions of [3a](2-) and [3b](2-) can be assigned almost completely to the electronic transitions within the Re(6)S(8) core. The different emission characteristics of the bis(bpy) complexes ([5a](2-) and [5b](2-)) from the tris(bpy) complex ([4](-)) are a result of the increase in the number of nitrogen donors on the Re(6)S(8) core, which stabilizes the Re(6)S(8) core energy to a lower level than the energy of the bpy ligand pi* orbital. On the other hand, it has been shown that the emissions of the bis(ppy) ([2a](2-) and [2b](2-)) and bis(bpe) complexes ([3a](2-) and [3b](2-)) are best characterized by the higher pi* energy level of each N-heteroaromatic ligand, which lead to a stronger metal character in the emissive excited state of the complex.

We conducted femtosecond transient absorption spectroscopy of oxymyoglobin (MbO(2)) in the wavelength region of 450-750 nm to observe the charge transfer (CT) state of the heme in MbO(2). The transient absorption spectrum just after photoexcitation (t = 0-0.25 ps) was assigned to superposition of S(1)-S(n) absorption (450-750 nm) and ground-state bleaching (540 and 580 nm) of MbO(2). At t0.25 ps, a new absorption band appeared at around 680 nm with the decay time of approximately 5 ps. This broad absorption band was similar to that of a porphyrin cation. Hence, we concluded that this absorption band was attributed to the ligand-to-metal charge transfer (LMCT) state of the heme. The proposed photophysical pathways suggested that formation of the LMCT state was the key event in the excited state relaxation of the heme in MbO(2).

The hexarhenium anionic cluster complex with terminal formate ligands [Re6S8(HCOO)6]4- was obtained by the room-temperature reaction between [Re6S8(OH)6]4- and formic acid in an aqueous solution. The cluster was crystallized as a potassium or cesium salt and characterized by X-ray single-crystal diffraction and elemental analyses, IR, 1H NMR, UV/vis, and luminescence spectroscopies. In particular, the emission quantum yield of the potassium salt of the Re6 cluster anion in the solid phase was determined for the first time. The electronic structures of [Re6S8(HCOO)6]4- and [Re6S8(OH)6]4- were also elucidated by DFT calculations.

In order to clarify the dynamics of phase transition from coiled states to globular states in a thermo-responsive polymer, poly( N -isopropylacrylamide) (PNIPAM), we developed a method of dynamic (time-resolved) fluorescence spectroscopy combined with a laser T-jump technique. Using this, we revealed the phase transition dynamics of fluorescent-labeled PNIPAM in aqueous solutions. The phase transition dynamics was reflected in a dynamic Stokes shift of a TICT fluorescence of the probe. The time constant of the phase transition ( τ ) was determined to be 35 μs, irrespective of the sample concentration studied (0.1–1.0 wt.%), and this was longer than that predicted from the diffusion–collision model.

The conversions of hexahydroxo rhenium cluster complexes [Re6Q8(OH)6]4- (Q = S, Se) in aqueous solutions in a wide pH range were investigated by chemical methods and spectroscopic measurements. Dep...

The paper describes the polarities of three fluorous ( F ) aliphatic alcohols: perfluorinated tert -butanol ( F - t -BuOH), n -butanol ( F - n -BuOH), and n -heptanol ( F - n -HepOH). For the purpose, we conducted absorption and fluorescence spectroscopies of coumarin 153 (C153) and 102 (C102) in three F and 13 non-fluorous (non- F ) alcohols and determined their maximum energies: ν a (absorption) and ν f (fluorescence). We obtained linear relationships between the Stokes shifts of the dyes (i.e., ( ν a − ν f )) and a medium polarity parameter for 13 non- F alcohols, f ( x ): f ( x ) = [( D s − 1)/(2 D s + 1) − ( n 2 − 1)/(2 n 2 + 1)], where D s and n were the dielectric constant and refractive index of a solvent, respectively. By comparing the Stokes shifts of the dyes in three F alcohols with those in 13 non- F alcohols (i.e., ( ν a − ν f ) vs. f ( x ) plot), the D s values in F - t -BuOH, F - n -BuOH, and F - n -HepOH were evaluated to be 2.7–3.9, 4.3–5.1, and 4.0–5.2, respectively, while those in the relevant non- F alcohols were 12.5, 17.5, and 12.9, respectively. Thus, the present experiments demonstrated that the polarities of these F alcohols were much lower than those of the relevant non- F alcohols.

Strongly luminescent mixed-metallic copper(I)-silver(I) coordination polymers with various Cu/Ag ratio were prepared by utilizing the isomorphous relationship of the luminescent parent homometallic coordination polymers (Φ(em) = 0.65 and 0.72 for the solid Cu and Ag polymers, respectively, at room temperature). The mixed-metallic polymer with the mole fraction of copper even as low as 0.005 exhibits a strong emission (Φ(em) = 0.75) from only the copper sites as the result of the efficient energy migration from the silver to the copper sites. The migration rates between the two sites were evaluated from the dependence of emission decays upon the mole fraction of copper.

A [Ru(phen)3](2+) complex (phen = 1,10-phenanthroline) having an arylethynyl group at the 4-position of one of the three phen ligands (aryl: (dimesityl)borylduryl group = [RuBE](2+) or duryl group = [RuDE](2+)) showed dual emissions at low temperature in propylene carbonate (PC). The shorter emission lifetime components (τ(em)(s) ≈ 13 μs) that originated from the lowest-energy excited triplet states (T1) of the complexes were almost independent of temperature (T = 77-320 K), while the longer emission lifetime components (τ(em)(l)), as the T2 emissions appeared below the fluid-to-glass transition temperature (Tg ≈ 220 K) in PC, were almost constant at 27 μs in the range of T = 77-220 K. The τ(em)(s) components of the complexes were assigned to the emissions from the metal-to-ligand charge transfer (MLCT) excited states possessing relatively large ligand-centered (LC) excited-state characters (T1(MLCT/LC)), while the τ(em)(l) components were shown to be originating from the T2(MLCT) excited states. The T2(MLCT) states of the complexes became nonemissive above Tg in PC due to fast nonradiative decay through solvent reorganization around the T2(MLCT) excited states. The photophysical properties of the complexes were also shown to be characterized by the presence of the arylethynyl units at the 4-positions of the phen ligands.

A series of Cu(I) complexes formulated as [Cu(2)(mu-X)(2)(PPh(3))(L)(n)] were prepared with various mono- and bidentate N-heteroaromatic ligands (X = Br, I; L = 4,4'-bipyridine, pyrazine, pyrimidine, 1,5-naphthyridine, 1,6-naphthyridine, quinazoline, N,N-dimethyl-4-aminopyridine, 3-benzoylpyridine, 4-benzoylpyridine; n = 1, 2). Single-crystal structure analyses revealed that all the complexes have planar {Cu(2)X(2)} units. Whereas those with monodentate N-heteroaromatic ligands afforded discrete dinuclear complexes, bidentate ligands formed infinite chain complexes with the ligands bridging the dimeric units. The long Cu...Cu distances (2.872-3.303 A) observed in these complexes indicated no substantial interaction between the two Cu(I) ions. The complexes showed strong emission at room temperature as well as at 80 K in the solid state. The emission spectra and lifetimes in the microsecond range were measured at room temperature and at 80 K. The emissions of the complexes varied from red to blue by the systematic selection of the N-heteroaromatic ligands (lambda(em)(max): 450 nm (L = N,N-dimethyl-4-aminopyridine) to 707 nm (L = pyrazine)), and were assigned to metal-to-ligand charge-transfer (MLCT) excited states with some mixing of the halide-to-ligand (XL) CT characters. The emission energies were successfully correlated with the reduction potentials of the coordinated N-heteroaromatic ligands, which were estimated by applying a simple modification based on the calculated stabilization energies of the ligands by protonation.

When a chloroform solution of a dicyano(diimine)platinum(II) complex, [Pt(CN)2(5,5‘-dinonyl-2,2‘-bipyridine)], was spread onto pure water, a reversible surface pressure−molecular area curve was obtained. The surface pressure began to increase steeply from 0 at a molecular area of 0.61 nm2 molecule-1. On further compression, the monolayer was stable at 0.2 nm2 molecule-1 and 30 mN m-1. In such a highly compressed state, the complex was thought to orient its planar ligand 2,2‘-bipyridine perpendicular to the water surface. The floating monolayer was vertically deposited onto a hydrophobic quartz substrate as an X-type film. The absorption spectra of the deposited films showed a broad peak at 480 nm, while that band was absent in the solution spectrum. The emission spectra of the films exhibited a broad band around 600 nm. The excitation spectra monitored at 600 nm coincided well with the absorption spectra. The results were interpreted in terms of the formation of the molecular aggregate, in which the plati...

This paper reviews recent advances in chemical applications of optical trapping of single microparticles in solution, with special reference to microspectroscopy (absorption, fluorescence, and Raman spectroscopy), interfacial processes across microdroplet/solution interfaces, and photochemical reactions in microdroplets. After describing the principles and experimental setups of optical trapping of single microparticles, recent topics of chemical applications of the techniques are described. The work on optical trapping-electrochemical measurements of single microdroplets is also summarized. In particular, this review focuses on demonstrating the characteristics of chemical processes in micrometer dimensions, i.e., “microchemistry”.