An all-inorganic polynuclear unit consisting of an oxo-bridged binuclear ZrOCoII group coupled to an iridium oxide nanocluster (IrO x ) was assembled on an SBA-15 silica mesopore surface. A ...photodeposition method was developed that affords coupling of the IrO x water oxidation catalyst with the Co donor center. The approach consists of excitation of the ZrOCoII metal-to-metal charge-transfer (MMCT) chromophore with visible light in the presence of Ir(acac)3 (acac: acetylacetonate) precursor followed by calcination under mild conditions, with each step monitored by optical and infrared spectroscopy. Illumination of the MMCT chromophore of the resulting ZrOCoII–IrO x units in the SBA-15 pores loaded with a mixture of 13CO2 and H2O vapor resulted in the formation of 13CO and O2 monitored by FT-IR and mass spectroscopy, respectively. Use of 18O labeled water resulted in the formation of 18O2 product. This is the first example of a closed photosynthetic cycle of carbon dioxide reduction by water using an all-inorganic polynuclear cluster featuring a molecularly defined light absorber. The observed activity implies successful competition of electron transfer between the IrO x catalyst cluster and the transient oxidized Co donor center with back electron transfer of the ZrOCo light absorber, and is further aided by the instant desorption of the CO and O2 product from the silica pores.
On the flipside: A reversible photochromic mechanism for the complex Ru(bpy)2(pySO)2+ (bpy=2,2′‐bipyridine, pySO=2‐(isopropylsulfinylmethyl)pyridine) is presented. Isomerization from the S‐bonded ...(see picture; blue) to the O‐bonded form (red) occurs upon excitation with UV light with a time constant τ of 1.5 ns (Φ=0.11), for the reverse process τ=6.3 ns (Φ=0.027).
The oxo-bridged heterobinuclear chromophore TiOMn2+ has been covalently anchored onto a silica nanoparticle surface, allowing for the preparation of optically transparent solid state samples. Optical ...spectra of the material yield a broad metal-to-metal charge-transfer (MMCT) transition in the UV with a tail extending to 550 nm. Fitting the absorption band to a Gaussian curve gives a maximum at 44 610 (±230) cm–1 (587 (±20) M–1 cm–1) with a full width at half-maximum of 17 320 (±160) cm–1, and yields an electronic coupling constant, H ABopt, of 4200 cm–1 by Hush analysis. Transient absorption measurements of transparent pressed pellets in vacuum yield a 2.43 (±0.20) μs lifetime at room temperature. The temperature dependence of the lifetime in the range of 10–40 °C gives an activation energy of 1.67 (±0.36) kcal/mol and pre-exponential factor A of 7.3 (±4.4) × 106 s–1. This temperature dependence results in an electronic coupling constant H ABkin of less than 1 cm–1. The disparity between the large electronic coupling indicated by fitting the absorption band and the very small coupling based on temperature dependent kinetic measurements suggests that the observed microsecond back electron transfer is from an electronic state that is distinct from the initially excited MMCT state. It is proposed that the initially excited high spin state (S = 5/2) branches on the ultrafast time scale between back electron transfer to the ground state (S = 5/2) and intersystem crossing to a low spin MMCT state (S = 3/2 or 1/2). With intersystem crossing to a lower spin state available as a competitive pathway, these robust chromophores are promising for driving multielectron catalysis in an integrated artificial photosynthesis system.
Photochromic Ru(bpy)2(OSO)(PF6), where bpy is 2,2′-bipyridine and OSO is 2-methylsulfinylbenzoate, was investigated by femtosecond transient absorption spectroscopy. The results show that for both S- ...and O-bonded isomers, a 3MLCT state is formed on a femtosecond time scale. Also observed is the formation of multiple metal-to-ligand charge-transfer (MLCT) states, representing different conformers, prior to isomerization on the picosecond time scale. These results and others are compiled in an energy diagram depicting these results.
A series of photochromic ruthenium sulfoxide complexes of the form Ru(bpy)2(OSOR)+, where bpy is 2,2′-bipyridine and OSOR is 2-(benzylsulfinyl)benzoate (OSOBn), ...2-(napthalen-2-yl-methylsulfinyl)-benzoate (OSONap), or 2-(pentafluorophenylmethanesulfinyl)benzoate (OSOBnF5), have been synthesized and characterized. In aggregate, the data are consistent with phototriggered isomerization of the sulfoxide from S-bonded to O-bonded. The S-bonded complexes feature 3MLCT absorption maxima at 388 nm (R = BnF5), 396 nm (R = Bn), and 400 nm (R = Nap). Upon charge transfer excitation the S-bonded peak diminishes concomitant with new peaks growing in at ∼350 and ∼495 nm. Spectroscopic and electrochemical data suggest that the electronic character of the substituent on the sulfur affects the properties of the S-bonded complexes, but not the O-bonded complexes. The isomerization is reversible in methanol solutions and, in the absence of light, thermally reverts to the S-bonded isomer with biexponential kinetics. The quantum yields of isomerization (Φs→o) were found to be 0.32, 0.22, and 0.16 for the R = BnF5, Bn, and Nap complexes, respectively. Kinetic analyses of femtosecond transient absorption data were consistent with a nonadiabatic mechanism in which isomerization occurs from a thermally relaxed 3MLCT state of S-bonded (or η2-sulfoxide) character directly to the singlet O-bonded ground state. The time constants of isomerization (τs→o) were found to be 84, 291, and 427 ps for the R = BnF5, Bn, and Nap complexes, respectively. Analysis of room temperature absorption and 77 K emission spectra reveal significant distortion between the S-bonded ground state (1GSS) and singlet metal-to-ligand charge transfer state (1MLCTS) and thermally relaxed 3MLCT, respectively. The distortion is primarily attributed to low frequency metal−ligand and SO vibrational modes, which are intrinsically involved in the isomerization pathway.
The spectroscopic properties of photochromic ruthenium sulfoxide complexes are reviewed. The mode of action is associated with an excited state S→O isomerization triggered by light. These complexes ...feature large, positive Ru3+/2+ reduction potentials indicative of stabilization of the Ru dπ orbital set. In addition, these compounds feature large quantum yields of isomerization. In aggregate, the data argue against a promoting role for the LF states and suggest that isomerization occurs from the CT potential energy surface. Picosecond transient absorption experiments indicate a change in the isomerization mechanism between mondentate sulfoxide complexes and chelating sulfoxide complexes. These results as well as potential energy diagrams for certain complexes are discussed.
Details of spectroscopic results obtained from studies of photochromic ruthenium sulfoxide complexes are discussed. These results are compared and lead to the conclusion that different mechanisms for excited state isomerization exist for these compounds.
Vineyard exposure to wildfire smoke can taint grapes and wine. To understand the impact of this taint, it is imperative that the analytical methods used are accurate and precise. This study compared ...the variance across nine commercial and research laboratories following quantitative analysis of the same set of smoke-tainted wines. In parallel, correlations between the interlaboratory consensus values for smoke-taint markers and sensory analyses of the same smoke-tainted wines were evaluated. For free guaiacol, the mean accuracy was 94 ± 11% in model wine, while the free cresols and 4-methylguaiacol showed a negative bias and/or decreased precision relative to guaiacol. Similar trends were observed in smoke-tainted wines, with the cresols and glycosidically bound markers demonstrating high variance. Collectively, the interlaboratory results show that data from a single laboratory can be used quantitatively to understand smoke-taint. Results from different laboratories, however, should not be directly compared due to the high variance between study participants. Correlations between consensus compositional data and sensory evaluations suggest the risk of perceivable smoke-taint can be predicted from free cresol concentrations, overcoming limitations associated with the occurrence of some volatile phenols, guaiacol in particular, as natural constituents of some grape cultivars and of the oak used for barrel maturation.
The aim of the present study was to clarify the mechanisms underlying body understanding by examining the impact of visual experience (magnification and reduction) on perception of hand size and ...neutral external objects (squares). Independent groups of participants were asked to look through a 2× magnification lens, a ½-× reduction lens, or a control UV filter and to make visual size judgments about square stimuli and their hands. In Experiment
1
, participants used a measuring device with unmarked wooden slats orientated in horizontal and radial/vertical space for their visual judgments. In Experiment
2
, participants used an upright frontal slat for visual length judgments of their hands to eliminate any potential foreshortening in viewing the measurement apparatus. The results from the two experiments demonstrate that participants significantly underestimated both the square stimuli and their hands when they viewed them under a reduction lens. While overestimation and underestimation of squares was found for females in Experiment
2
, males generally underestimated the squares. However, overestimation was not seen when the participants viewed their hands under a magnification lens. Implications of these findings are discussed.
Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N′-phenylene-bis-(3,5-di-tert-butylsalicylideneimine); ZnL R ) complexes. A structurally related family of ZnL ...R complexes (R = OMe, di-tBu, tBu, Cl, NO2) were prepared, and the mechanisms of fluorescence quenching by nitroaromatics were studied by a combined kinetics and spectroscopic approach. The fluorescent quantum yields for ZnL R were generally high (Φ ∼ 0.3) with sub-nanosecond fluorescence lifetimes. The fluorescence of ZnL R was quenched by nitroaromatic compounds by a mixture of static and dynamic pathways, reflecting the ZnL R ligand bulk and reduction potential. Steady-state Stern-Volmer plots were curved for ZnL R with less-bulky substituents (R = OMe, NO2), suggesting that both static and dynamic pathways were important for quenching. Transient Stern-Volmer data indicated that the dynamic pathway dominated quenching for ZnL R with bulky substituents (R = tBu, DtBu). The quenching rate constants with varied nitroaromatics (ArNO2) followed the driving force dependence predicted for bimolecular electron transfer: ZnL* + ArNO2 → ZnL + + ArNO2 −. A treatment of the diffusion-corrected quenching rates with Marcus theory yielded a modest reorganization energy (λ = 25 kcal/mol), and a small self-exchange reorganization energy for ZnL*/ZnL + (ca. 20 kcal/mol) was estimated from the Marcus cross-relation, suggesting that metal phenoxyls may be robust biological redox cofactors. Electronic structure calculations indicated very small changes in bond distances for the ZnL → ZnL + oxidation, suggesting that solvation was the dominant contributor to the observed reorganization energy. These mechanistic insights provide information that will be helpful to further develop ZnL R as sensors, as well as for potential photoinduced charge transfer chemistry.
The complexes Ru(bpy)2(OS)(PF6) and Ru(bpy)2(OSO)(PF6), where bpy is 2,2′-bipyridine, OS is 2-methylthiobenzoate, and OSO is 2-methylsulfinylbenzoate, have been studied. The electrochemical and ...photochemical reactivity of Ru(bpy)2(OSO)+ is consistent with an isomerization of the bound sulfoxide from S-bonded (S-) to O-bonded (O-) following irradiation or electrochemical oxidation. Charge transfer excitation of Ru(bpy)2(OSO)+ in MeOH results in the appearance of two new metal-to-ligand charge transfer (MLCT) maxima at 355 and 496 nm, while the peak at 396 nm diminishes in intensity. The isomerization is reversible at room temperature in alcohol or propylene carbonate solution. In the absence of light, solutions of O-Ru(bpy)2(OSO)+ revert to S-Ru(bpy)2(OSO)+. Kinetic analysis reveals a biexponential decay with rate constants of 5.66(3) × 10−4 s−1 and 3.1(1) × 10−5 s−1. Cyclic voltammograms of S-Ru(bpy)2(OSO)+ are consistent with electron-transfer-triggered isomerization of the sulfoxide. Analysis of these voltammograms reveal E S°′ = 0.86 V and E O°′ = 0.49 V versus Ag/Ag+ for the S- and O-bonded Ru3+/2+ couples, respectively, in propylene carbonate. We found k S→O = 0.090(15) s−1 in propylene carbonate and k S→O = 0.11(3) s−1 in acetonitrile on RuIII, which is considerably slower than has been reported for other sulfoxide isomerizations on ruthenium polypyridyl complexes following oxidation. The photoisomerization quantum yield (ΦS→O = 0.45, methanol) is quite large, indicating a rapid excited state isomerization rate constant. The kinetic trace at 500 nm is monoexponential with τ = 150 ps, which is assigned to the excited S→O isomerization rate. There is no spectroscopic or kinetic evidence for an O-bonded 3MLCT excited state in the spectral evolution of S-Ru(bpy)2(OSO)+ to O-Ru(bpy)2(OSO)+. Thus, isomerization occurs nonadiabatically from an S-bonded (or η2-sulfoxide) 3MLCT excited state to an O-bonded ground state. Density functional theory calculations support the assigned spectroscopy and provide insight into ruthenium ligand bonding.
