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The starburst-type arylborane-appended polypyridyl RuII complex [Ru{4,7-bis({dimesityl}boryldurylethynyl)-1,10-phenanthroline}3]2+ (1) was synthesized, and its spectroscopic and photophysical properties were evaluated. In the excited state of the complex, intramolecular charge transfer (CT) between the π orbital of the aryl group and the vacant p orbital of the boron atom [π(aryl)–p(B) CT] interacts synergistically with metal-to-ligand charge transfer (MLCT). The synergistic CT interactions in 1 are more effective than those in previously reported arylborane-appended polypyridyl RuII complexes and lead to bright (molar absorption coefficient of the MLCT band = 7.2 × 104 m–1 cm–1, emission quantum yield = 0.29) and long-lived emission (8.7 µs) of 1 in CH3CN at 298 K. The unique emission characteristics of 1 are discussed in detail together with its electrochemical properties and time-dependent DFT (TD-DFT) calculations.

An introduction of two arylborane charge transfer (CT) units to the periphery of 1,10-phenanthroline (B2phen) or 2,2′-bipyridine (B2bpy) in a tricarbonyl rhenium(I) diimine complex (fac-[Re(CO)3(B2phen)Br] = ReB2phen or fac-[Re(CO)3(B2bpy)Br] = ReB2bpy) resulted in unique redox, spectroscopic, and photophysical properties of the complex. In particular, the presence of the two arylborane units in the complex can enhance its metal-to-ligand CT absorption intensity in the visible region and the radiative rate constant, compared to those of the complexes without and with the single arylborane unit in the ligand. The single X-ray crystal structure of ReB2phen is also reported.

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...

We report the synthesis and photophysical properties of a novel tricarbonyl rhenium(I) complex having a (dimesityl)boryldurylethynyl (DBDE) group at the 4-position of a 2,2′-bipyridine (bpy) ligand, fac -[Re(CO) 3 (DBDE-bpy)Br] = ReBbpy , and discuss the diimine ligand structure effects on the spectroscopic and photophysical properties of the complex by comparing with those of the relevant 4-DBDE-1,10-phenanthroline (phen) type complex: fac -[Re(CO) 3 (DBDE-phen)Br] = ReBphen . The present study demonstrated that ReBbpy showed smaller DBDE effects on the spectroscopic and photophysical properties compared with ReBphen , whose origin was discussed in terms of the redox, absorption/emission, and time-dependent density functional theory calculation data on the complexes.

The reaction of a K4[\Re6Si8\(OH)a6]·8H2O rhenium cluster salt with 4,4'-bipyridine (bpy) or 4-aminopyridine (apy) in an aq. soln. at mild temp. and pressure conditions lead to cluster functionalization and to the formation of two new compds. [\Re6Si8\(OH)a2(bpy)a4]·bpy·4H2O (1) and [\Re6Si8\(OH)a2(apy)a4]·2apy·2H2O (2). Their crystal structures are built up from trans-[\Re6Si8\(OH)a2(L)a4] neutral units and the cohesions of both supramol. frameworks are based on π-π stacking as well as hydrogen bonds, involving the cluster units trans-[\Re6Si8\(OH)a2(L)a4], interstitial L ligands and water mols. 1 and 2 present 2D and 3D cluster frameworks, resp. Both compds. show red-NIR luminescence in the solid states. DFT calcns. demonstrate that assocn. of face capped Re6 clusters with bpy and apy ligands enabled to form supramol. frameworks that retain luminescent properties of the cluster units.

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.

The photoredox ability of a hexarhenium(III) cluster, [Re6(μ 3-S)8Cl6]4−, in acetonitrile was examined on the basis of the emission quenching experiments of the cluster by a series of neutral organic electron acceptors (A). The photoinduced electron transfer quenching rate constants and the relevant activation parameters demonstrated that the hexarhenium(III) cluster acted as a useful photoredox sensitizer towards various A and the system gave a high charge separation yield owing to electrostatic repulsion between the product ions: [Re6(μ 3-S)8Cl6]3− and A −. These results were proved explicitly by nanosecond transient absorption spectroscopy.

New polymerisable photoluminescent octahedral rhenium cluster complexes trans-[{Re6Q8}(TBP)4(VB)2] (Q = S or Se; TBP-p-tert-butylpyridine; VB-vinyl benzoate) have been synthesised, characterised and used to construct rhenium cluster-organic polymer hybrid materials. These novel polymer systems are solution-processable and the rhenium clusters retain their photoluminescent properties within the polymer environment. Notably, when the rhenium cluster complexes are incorporated into the matrix of the electroluminescent polymer poly(N-vinylcarbazole), the resultant cluster polymer hybrid combined properties of both components and was used successfully in the construction of a polymer light emitting diode (PLED). These prototype devices are the first PLEDs to incorporate octahedral rhenium clusters and provide the first direct evidence of the electroluminescent properties of rhenium clusters and indeed, to the best of our knowledge, of any member of the family of 24-electron hexanuclear cluster complexes of molybdenum, tungsten or rhenium.

We demonstrate that a poly(N-isopropylacrylamide) (PNIPAM) microassembly, formed by plasmonic optical trapping, can provide the platform for a highly sensitive detection technique for fluorescent and nonfluorescent organic molecules dissolved in aqueous solution. PNIPAM microassemblies can be easily formed by a combination with a photothermal effect and an enhanced optical force. These physical phenomena were obtained through resonant excitation of localized surface plasmon (LSP). Sparsely distributed fluorescent or nonfluorescent molecules dissolved in solution can be extracted into the PNIPAM assembly, resulting in an increase in fluorescence or Raman signals. In particular, we successfully detected quite small amounts of analytes (rhodamine B) at the 10–9 mol/L level. Using LSP is an alternative approach in analytical chemistry and can be used in addition to surface enhanced Raman scattering and surface enhanced fluorescence.

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.

This article describes the synthesis, structures and systematic study of the spectroscopic and redox properties of a series of octahedral molybdenum metal cluster complexes with aromatic sulfonate ligands (nBu4N)2[{Mo6X8}(OTs)6] and (nBu4N)2[{Mo6X8}(PhSO3)6] (where X- is Cl-, Br- or I-; OTs- is p-toluenesulfonate and PhSO3 - is benzenesulfonate). All the complexes demonstrated photoluminescence in the red region and an ability to generate singlet oxygen. Notably, the highest quantum yields (>0.6) and narrowest emission bands were found for complexes with a {Mo6I8}4+ cluster core. Moreover, cyclic voltammetric studies revealed that (nBu4N)2[{Mo6X8}(OTs)6] and (nBu4N)2[{Mo6X8}(PhSO3)6] confer enhanced stability towards electrochemical oxidation relative to corresponding starting complexes (nBu4N)2[{Mo6X8}X6].

An efficient and versatile method was established for the preparation of 1,3a,6a-triazapentalenes. The 1,3a,6a-triazapentalene skeleton without an additional fused ring system was discovered to be a compact and highly fluorescent chromophore, which exhibited various interesting fluorescent properties such as a noteworthy correlation of luminescent wavelength with the Hammett σ(p) value and a strongly positive solvatofluorochromism.

Localized-surface-plasmon (LSP)-enhancement effect on one-photon photochromic ring-opening reaction of two diarylethene (DE) derivatives was studied using absorption spectroscopy. DEs were doped in polymer films and those were coated onto Au-nanoparticles-integrated substrates. Acceleration of the one-photon photochromic reactions was observed in the presence of Au nanoparticles. The origin of the behavior was attributed to an enhancement effect of incident electromagnetic field by LSP. An alternative mechanism, i.e., photothermal effect was also experimentally examined and discussed.

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.

The spectroscopic and photophysical properties of 1,3-di(9-anthryl)benzene (DAB), 1,3,5-tri(9-anthryl)benzene (TAB), and tri(9-anthryl)borane (TABO) in tetrahydrofuran were reported, together with those of 9-phenylanthracene (MAB). Although MAB, DAB, and TAB showed structured absorption spectra similar to the 1La band of anthracene in the wavelength region of 300–400 nm, the molar absorption coefficient at the maximum wavelength of TAB was as large as ∼4.2 as compared with that of MAB. Detailed analysis of the absorption data indicated that the absorption transition moment of MAB, DAB, or TAB was 3.3, 4.3, or 6.4 D, respectively. The large absorption transition moment of TAB was discussed on the basis of the electron density distributions in the highest-energy occupied and lowest-energy unoccupied molecular orbitals. In contrast to TAB, TABO exhibited characteristic broad and structureless absorption and fluorescence spectra. The large differences in the spectroscopic and photophysical properties between TAB and TABO were discussed in terms of the effects of the chemical structure of the terminal unit connecting three anthryl groups.

We demonstrate that a photochromic reaction can be driven by irradiation from a weak, near-infrared continuous-wave (NIR-CW) laser light. A two-photon ring-opening photochromic reaction of a diarylethene (DE) derivative can be induced by irradiation with a NIR-CW laser light (lambda = 808 nm). An ultrathin polymer film doped with DE in its closed form was coated onto a gold-nanoparticle-integrated glass substrate. Upon irradiation of the sample with a CW laser at low fluence (0.1-4.0 W/cm(2)), we could clearly observe bleaching of the DE (ring-opening reaction). Following the IR irradiation, the bleached absorption could be reversibly recovered by applying UV irradiation (ring-closing reaction). We verified that the yield of the photochromic ring-opening reaction of the DE was proportional to the square of the irradiation fluence. The origin of this NIR-CW-induced two-photon photochromic reaction is an "enhancing effect" that acts on the electromagnetic field (localized surface plasmon) of the gold nanoparticles. The DE interacts with the surface plasmon and receives energy from two photons, which excites it to a state from which the ring-opening reaction can be initiated.

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).

Silica gel beads (diameter ∼10 μm) covalently modified with metal-free monopyridyltriphenylporphyrin (PyTPP) via a silane coupling reagent (PyTPP-SiO 2 ) were introduced into a polymer microchannel and, the microchip was applied to photodecomposition of phenol under solution-flow conditions. The photodecomposition yield of phenol in the microchannel was dependent on the solution-flow rate ( ν ) and increased with decreasing ν . At ν = 0.5 μL/min, the decomposition yield was as high as 93% with the reaction time of 42 s, while that in a bulk aqueous PyTPP-SiO 2 suspension was 73% with the reaction time of 2 h. In the microchannel chip experiments, furthermore, the yield increased with decreasing the thickness of the solution-flow layer above the PyTPP-SiO 2 particles. On the basis of optical trapping-absorption microspectroscopy of single PyTPP-SiO 2 particles before and after the photoreaction, we discuss characteristics of the photoreaction in the microchannel accommodated with PyTPP-SiO 2 particles.

Reductive photocyanation of 1,10-phenanthroline (phen) took place in an aqueous NaCN solution, yielding 5-cyano-5,6-dihydro-1,10-phenanthroline (Hphen-CN) with the reaction and quantum yields of 5–50% and 10 −3 to 10 −4 , respectively. The photoreaction in the presence of Mg 2+ (aerated conditions) improved the reaction quantum yield by a factor of ∼7 as compared to that without Mg 2+ , through coordination of Mg 2+ with phen: phen:Mg 2+ complex. The fluorescence lifetimes of phen and the phen:Mg 2+ complex were ∼3 and ∼10 ns, respectively, and the fluorescence of the phen:Mg 2+ complex was shown to be quenched more efficiently by a cyanide ion as compared to that of phen itself. The fluorescence quenching percents of phen by NaCN in the absence and presence of Mg 2+ were 3 and 24%, respectively, and the eight-fold increase in the quenching percent in the presence of Mg 2+ gave rise to the approximately seven-fold increase in the reaction quantum yield. On the basis of such results, we proposed that the present photocyanation reaction proceeded via electron transfer from a cyanide ion to the excited singlet-states of phen and/or the phen:Mg 2+ complex as the primary step: anion radical (S N-R 1Ar*) mechanism. The characteristic features of the present photoreaction of phen in the presence of Mg 2+ and the possible reaction mechanisms are discussed in detail.

Photoirradiation of perylene in the presence of 1,4-dicyanobenzene and NaCN in a benzonitrile (BN)/water emulsion under vigorous stirring gave 1- and 3-cyanoperylene in a total yield of 15%. For kinetic and mechanistic studies of the photoreaction, we conducted single-droplet measurements by using a laser trapping-microspectroscopy technique. Although determination of the incident light intensity absorbed by a solute in the emulsion is in general very difficult owing to strong light scattering, that in single laser-trapped BN droplets dispersed in water was successful on the basis of the photooxidation reaction of 9,10-disubstituted anthracene. The quantum yield of the photocyanation of perylene (ΦCN) was then determined to be 4.9×10−3. Furthermore, we found that ΦCN was linearly proportional to the inverse of the droplet radius: the reaction efficiency increased with decreasing droplet size through an increase in the surface area/volume (A/V) ratio of a droplet. This is the first demonstration of micrometre droplet size effects on the quantum yield for a photoreaction across the droplet/water interface.

A CS4−:(RuB32+)2 hybrid complex as a new class of a chemosensor was prepared by an ion-exchange reaction, where CS4− and RuB32+ were calix[4]arenetetrasulfonate and a tris(2,2′-bipyridine)ruthenium(II) dication, respectively. In the solid state, one RuB32+ was shown to bury partly in the cavity of CS4− from the upper rim, while other RuB32+ sits near the CS4−:RuB32+ ion-pair to balance the total electric charge of the hybrid. In methanol, on the other hand, two RuB32+ molecules in the hybrid complex located in the vicinity of a CS4− molecule at analogous microenvironments as suggested by 1 H -NMR. Spectroscopic and excited-state properties of RuB32+ in the hybrid were influenced by CS4− through the ion-excited dipole interaction and photoinduced electron transfer quenching. In the presence of a foreign cation as a guest, the emission intensity and lifetime of RuB32+ increased, demonstrating that CS4−:(RuB32+)2 hybrid complex acted as a luminescent chemosensor. The mechanism of ion recognition was discussed in terms of changes in the photophysical properties of the hybrid complex.

Tris[2-{3-(dimesitylboryl)phenyl}pyridinato]iridium(III) ([Ir(Bppy)3]) showed bright green-phosphorescence with the emission lifetime and quantum yield of 1.0–1.4 µs and 1.0, respectively, in nonpo...

The fluorescence dynamics of Rhodamine 6G (R6G) in ethylene glycol/water (EG/W) microdroplets dispersed in a polydimethylsiloxane (PDMS) solid matrix were studied by picosecond time-resolved microspectroscopy. The large decrease in the fluorescence lifetime of R6G was observed for the droplets with the diameter (d) below 10 μm and at the R6G concentrations ([R6G]) above 0.1 mM. Absorption microspectroscopy revealed that the dimer formation of R6G in EG/W microdroplets was facilitated with decreasing d and increasing [R6G]. The size-dependent fluorescence lifetime of R6G was related to quenching of the monomer excited state by the R6G dimer. The origin of size-dependent dimer formation and, thus, the size-dependent fluorescence lifetime of R6G in micrometer-sized droplets in the PDMS matrix was discussed in detail.

Optical trapping of lysozyme, cytochrome c, or myoglobin based on photon pressure generated by focusing 1064 nm laser beam in an aqueous solution was explored. For all the proteins, microparticle formation was observed at the focal point under an optical microscope. Furthermore, the microparticles were identified to the molecular assemblies of the corresponding protein by means of confocal Raman microspectroscopy. For lysozyme, molecular clusters in solution were optically trapped to form the microparticle and it took more than 1 h to produce the microparticle. By contrast, molecular assembling proceeded within 1 min for cytochrome c and myoglobin. Since heme in cytochrome c or myoglobin would have a high polarizability, that would contribute to rapid assembling of the protein. Thus we demonstrated that a focused laser beam was a powerful tool to manipulate protein molecules in solution.

CdS Nanocrystal/Chelate Polymer Hybrid Systems: Controls of Optical and Morphological Properties by Monochromatic Photoirradiation

The spectroscopic and photophysical properties of triarylborane derivatives were controlled by the nature of the triarylborane core (trixylyl- or trianthrylborane) and peripheral electron-donating groups (N,N-diphenylamino or 9H-carbazolyl groups). The triarylborane derivatives with and without the electron-donating groups showed intramolecular charge-transfer absorption/fluorescence transitions between the π orbital of the aryl group (π(aryl)) and the vacant p orbital on the boron atom (p(B), π(aryl)-p(B) CT), and the fluorescence color was tunable from blue to red by the combination of peripheral electron-donating groups and a triarylborane core. Detailed electrochemical, spectroscopic, and photophysical studies of the derivatives, including solvent dependences of the spectroscopic and photophysical properties, demonstrated that the HOMO and LUMO of each derivative were determined primarily by the nature of the peripheral electron-donating group and the triarylborane core, respectively. The effects of solvent polarity on the fluorescence quantum yield and lifetime of the derivatives were also tunable by the choice of the triarylborane core.

Orange single crystals of K4 [Re6Sei8 (N3)a6]·4H2O are obtained by mixing aqueous solutions of NaN3 and K4 [Re6Sei8(OH)a6] ·8H2O.

Mass transfer processes of ferrocene derivatives (FeCp−X) across a single-nitrobenzene-microdroplet/water interface were studied by laser-trapping and microelectrochemical techniques. Substituent e...

A one-pot synthetic method was established for the preparation of 2,5-disubstituted-1,3a,6a-triazapentalenes. The fluorescence observation of the synthetic 2,5-disubstituted-1,3a,6a-triazapentalenes revealed that the introduction of a substituent at the C5 position allowed a substantial change in the fluorescence quantum yield with little effect on the fluorescence wavelength.

A novel radical trapping technique combined with a fluorescence spectroscopic analysis has been employed to investigate the radical intermediates produced by photodecarboxylation of four synthetic pyrethroids: fenvalerate (SMD), fenpropathrin (DTL), cyphenothrin (GKL), and cypermethrin (AGT). Under photoirradiation at >290 nm, all pyrethroids underwent direct photolysis via homolytic cleavage of the carbon–oxygen bonds in the ester groups. The consumed amount of a nitroxide free radical, as a trapping agent for the intermediate radical of a pyrethroid, was determined by ESR, which was the measure of the reaction yield of a photochemically generated α-cyano-3-phenoxybenzyl radical common to all pyrethroids. The reactivities of the pyrethroids studied was in the sequence of SMD ≫ DTL > GKL > AGT. Furthermore, nanosecond transient absorption spectroscopy demonstrated that geminate recombination of the radical pair within a solvent cage is the main deactivation route of the photochemically generated α-cyano-3-phenoxybenzyl radical common for all pyrethroids studied.

We report the synthesis and photophysical/photoredox characteristics of a novel tricarbonyl rhenium(I) complex having a (dimesityl)boryldurylethynyl (DBDE) group at the 4-position of a 1,10-phenanthroline (phen) ligand, [Re(CO)(3)(4-DBDE-phen)Br] (ReB). ReB in tetrahydrofuran at 298 K showed the metal-to-ligand charge transfer (MLCT) emission at around 681 nm with the lifetime (τ(em)) of 900 ns. The relatively long emission lifetime of ReB compared with that of [Re(CO)(3)(phen)Br] (RePhen, τ(em) = 390 ns) was discussed on the basis of the temperature dependent τ(em) and Franck-Condon analysis of the emission spectra of the two complexes. Emission quenching studies of both ReB and RePhen by a series of electron donors revealed that the photoinduced electron transfer (PET) quenching rate constant of ReB was faster than that of RePhen at a given Gibbs free energy change of the PET reaction (ΔG(ET)(0)-0.5 eV). All of the results on ReB were discussed in terms of the contribution of the CT interaction between the π-orbital(s) of the aryl group(s) and the vacant p-orbital on the boron atom in DBDE to the MLCT state of the complex.

Photoirradiation of a poly(2-hydroxyethyl methacrylate) (PHEMA) film with an acetonitrile solution of arylalkene or arylcyclopropane (S, aryl group; phenanthryl or pyrenyl group) in the presence of dimethylterephthalate (DMTP) as an electron acceptor gave an aryl-modified polymer surface. Introduction of the aryl group to the film was confirmed by spectroscopic methods. Mechanistic investigations indicated that a key intermediate of the photoreaction was the cation radical of S produced by one-electron transfer from the excited singlet state of S to DMTP. In addition to the factors controlling the reaction, properties of the modified polymer surface and micrometer fluorescent patterning of the film are also reported

Platinum (Pt) micropatterns were fabricated photocatalytically on titanium oxide (TiO2) surface by projecting a reduced light image of a photomask. Negative and positive Pt patterns on TiO2 with the spatial resolution better than 10 μm were obtained by photoreduction of PtCl42− to Pt in aqueous K2PtCl4 solution and photoetching of the deposited Pt in aqueous HCl solution, respectively.

The importance of micrometre dimensions in photochemistry is considered, and a systematic study on laser spectroscopy and photochemistry in small micrometre volumes is reported. To measure chemical reactions in the small volumes, submicrometre space- and picosecond time-resolved fluorescence and transient absorption spectroscopy was developed by employing a confocal laser scanning microscope. Laser-trapping phenomena were used for choosing small (micrometre-sized) materials as well as reagents, transferring them to a certain position with micrometre resolution and inducing chemical reactions. Combined with spectroscopic analysis, the laser-trapping technique was developed as a laser manipulation—spectroscopy—reaction method. Utilizing these methods, characteristic micrometre-sized effects were confirmed in the excimer dynamics in microdroplets and photoresponse of gels. Some small (micrometre-sized) reaction fields, which are crucial for conducting chemical reactions, were created by microfabrication techniques. Summarizing our trials, our goal to create an integrated chemical system named microphotoconversion is presented.

Picosecond fluorescence dynamics of triphenylmethane dyes bonded to polyacrylamide gels before and after swelling was studied by a single-photon timing technique. Microviscosity in the gels after swelling was estimated to be 10–11 cP by examining the viscosity dependence of fluorescence dynamics of malachite green in various alcohols. The results were interpreted in terms of structured stiff water in a microcavity of the gels.

Introduction of pyrenyl group to surface of a poly(2-hydroxyethyl methacrylate) (PHEMA) film was achieved by photoreaction of the film with an acetonitrile solution containing 1-(1-pyrenyl)-2-methylpropene and dimethyl terephthalate (DMTP). Spatial patterning of the film was also explored to show a possible application of the method to microfabrication with photo-functional molecules.

Spectral fitting was done on time- and temperature-dependent emission spectra of Ru(bpy){sub 3}{sup 2+} (bpy = 2,2{prime}-bipyridine) around the glass-to-fluid transition temperature of ethanol-methanol (4/1 v/v). With increasing time after excitation or with increasing temperature, the emission spectrum showed (i) a low-energy shift of the maximum, (ii) an increase in the intensity of the 0-1 vibrational band relative to that of the 0-0 band, and (iii) broadening the vibrational bands. These changes in the spectrum were ascribed to dynamic solvation change, leading to stabilization of the metal-to-ligand charge-transfer (MLCT) excited state and an increase in distortion between the ground and excited states. The time-dependent emission shift is accompanied by time-dependent nonradiative decay from the MLCT excited state.

It was found that the TICT (twisted intramolecular charge transfer) fluorescence of the title compound was very different in chlorinated solvents in comparison with other solvent systems. The emission energy from the a* state (charge transfer state) is higher and the intensity ratio, R=I a /I b where I a and I b are the emission intensity from the a* state and from the local excited state, is lower at room temperature in CHCl 3 and butyl chloride than in nonchlorinated solvents

Synthesis, redox, spectroscopic, and photophysical properties of a new class of Pt(II) complexes of the type [PtLnCl]+ are reported, where Ln is 4'-phenyl(dimesitylboryl)-2,2':6',2"-terpyridine (L1) or 4'-duryl(dimesitylboryl)-2,2':6',2"-terpyridine (L2). The free L1 or L2 ligand in CH3CN shows the absorption band responsible for intramolecular charge transfer (CT) from the pi-orbital of the aryl group in L1 or L2 (pi(aryl)) to the vacant p-orbital on the boron atom (p(B)), in addition to pipi* absorption in the 2,2':6',2"-terpyridine (tpy) unit. In particular, the L1 ligand shows an intense CT absorption band as compared with L2. Such intramolecular pi(aryl)-p(B) CT interactions in L1 give rise to large influences on the redox, spectroscopic, and photophysical properties of [PtL1Cl]+. In practice, [PtL1Cl]+ shows strong room-temperature emission in CHCl3 with the quantum yield and lifetime of 0.011 and 0.6 micros, respectively, which has been explained by synergetic effects of Pt(II)-to-L1 MLCT and pi(aryl)-p(B) CT interactions on the electronic structures of the complex. In the case of [PtL2Cl]+, the dihedral angle between the planes produced by the tpy and duryl(dimesitylborane) groups is very large (84 degrees ) as compared with that between the tpy and phenyl(dimesitylborane) units in [PtL1Cl]+ (26-39 degrees ), which disturbs electron communication between the Pt(II)-tpy and arylborane units in [PtL2Cl]+. Thus, [PtL2Cl]+ is nonemissive at room temperature. The important roles of the synergetic CT interactions in the excited-state properties of the [PtL1Cl]+ complex are shown clearly by emission quenching of the complex by a fluoride ion. The X-ray crystal structure of [PtL1Cl]+ is also reported.

New hybrid complexes of polypyridyl ruthenium and pyridylporphyrins have been prepared by the coordination of pyridyl nitrogens to the ruthenium centers. A 1:4 hybrid complex, [{Ru(bpy)(trpy)}4(mu4-H2Py4P)]8+ ([1]8+) (bpy = 2,2'-bipyridine; trpy = 2,2':6',2"-terpyridine; H2Py4P = 5,10,15,20-tetra(4-pyridyl)porphyrin), has been characterized by the single-crystal X-ray diffraction method. A 1:1 complex, [{Ru(bpy)(trpy)}(H2PyT3P)]2+ ([2]2+) (H2PyT3P = 5-(4-pyridyl)tritolylporphyrin) has also been prepared. The Soret band of the porphyrin ring shifts to longer wavelength with some broadening, the extent of the shift being larger for [1]8+. Cyclic voltammograms of the two complexes show simple overlap of the component redox waves. The complexes are weakly emissive at room temperature, which becomes stronger at lower temperatures. While [1]8+ at >140 K and [2]2+ at 77-280 K show only porphyrin fluorescence, [1]8+ at

Several microchemical techniques capable of investigating reactions proceeding in micrometer small volumes have been developed over the years [1, 2, 3]. As an example, space- and time-resolved absorption and emission spectroscopies based on an ultrafast laser and an optical microscope were successfully applied to studying characteristic features of photochemistry and photophysics in micrometer-picosecond dimensions [4, 5, 6]. Furthermore, an optical trapping method has been introduced for manipulating very small samples, by which individual microparticles, microdroplets, and so forth undergoing Brownian motion in solution can be manipulated arbitrarily in three-dimensional space by a focused infrared laser beam [7,8]. Since the optical trapping method provides noncontact and nondestructive manipulation of a single microparticle in solution, a combination of the technique with various microchemical methods opens a new research field of “chemistry of single microparticles” [9, 10, 11]. It is worth noting that, since a noncontact and nondestructive manipulation method for individual microparticles in solution was unavailable until the introduction of the optical trapping technique, experimental results obtained so far for microparticles are regarded as the sum or average of those for particles with various properties and diameters. In particular, chemical processes in a microparticle or across a microparticle/solution interface are dependent on the particle size, since the surface area (A = 4πr 2)/volume (V = (4/3)πr 3) ratio (A/V ~ 1/r) of a particle increases with decrease in the particle size (r = particle radius). Therefore, the roles of the interface become more important with increasing the A/V ratio of a particle. These discussions indicate clearly that ensemble measurements by particle-unresolved methods cannot afford a clear picture of the chemistry of microparticles. An optical trapping-microchemical method therefore contributes greatly to the understanding of chemical reactions proceeding in individual microparticles or across a particle/solution boundary [9, 10, 11].

Bifunctional dithiolene ligands have been coordinated to the Mo(V)(O)(μ-S2)Mo(V)(O) unit to afford [Mo2O2(μ-S)2(BPyDTS2)2](2-) (1(2-)) (BPyDTS2 (2-bis-(2-pyridyl)methylene-1,3-dithiolene) dianions. Reaction of the 1(2-) molybdenum dimer with pentacarbonylchlorothenium(i) affords a tetrametallic complex of formula [Mo2O2(μ-S)2(BPyDTS2)2{Re(CO)3Cl}2](2-) (2(2-)). The monomeric (CH3)2Sn(BPyDTS2) (3) tin complex has also been prepared for comparative purposes. In the structure of (Et4N)2[1], the two metal atoms are in a square pyramidal coordination environment defined by two bridging sulfur atoms, one terminal oxygen atom and the two sulfur atoms of the bifunctional dithiolene ligand. This arrangement leaves two nitrogen atoms on each side which coordinate to two Re atoms in the 2(2-) tetrametallic complex. Compound 3 has a distorted tetrahedral structure defined by two carbon atoms of the methyl groups and two sulfur atoms of the dithiolene ligand. The luminescence properties of all three complexes in acetonitrile have been investigated. Detailed studies supported on quantum mechanical calculations revealed that complex 1(2-) shows photoluminescence in the 600-800 nm region with a maximum wavelength of 628 nm and an emission quantum yield of 0.092, associated with an intraligand charge transfer (ILCT) transition. Coordination of two Re(CO)3Cl fragments to 1(2-) to afford 2(2-) does not affect the emission spectrum and shape although it decreases the quantum yield, approximately by a factor of 4.6. Compound 3 exhibits a similar emission spectrum to those of the complexes 1(2-) and 2(2-) in good agreement with the ILCT assignment. The quantum yield of 3 lies between that of the 1(2-) and 2(2-) complexes.