Fluorescence decay kinetics of acetone vapour at low pressures

Acetone-h₆ and -d₆ were excited by a short UV laser pulse to the nπ* state. Using pressures of 10^?4-10 ^?3 Torr, two distinct decay components were observed - the faster with a decay time of less than 20 ns and the slower of about 5 μs. Increasing the pressure leads to the appearance of two longer-lived decay components, which are apparently absent in the case of isolated molecules. Based on the deuteration effect, excitation wavelength dependence, quenching kinetics and analogy with other molecules, the four decay components are assigned as follows. The fastest component is due to dephasing of the initially excited state, forming a quasi-stationary eigenstate. The second component is due to the radiative decay of the latter states. The third, to decay of triplet states not directly coupled to the initially excited singlet states, and the last to the thermalized triplet state.     

Probing the Reactivity and Radical Nature of Oxidized Transition Metal-Thiolate Complexes by Mass Spectrometry

Transition metal thiolate complexes such as [PPN]⁺[RuL₃]^- (PPN?=?bis(triphenylphosphoranylidene) ammonium and L?=?diphenylphosphinobenzenethiolate) are known to undergo addition reactions with unsaturated hydrocarbons via the formation of new C-S bonds in solution upon oxidation. The reaction mechanism is proposed to involve metal-stabilized thiyl radical intermediates, a new type of distonic ions such as [RuL₃]⁺ ion in the case of [PPN]⁺[RuL₃]^-. This study presents the reactivity and structure investigation of [RuL₃]⁺ by mass spectrometry (MS) in conjunction with ion/molecule reactions. The addition reactions of [RuL₃]⁺ with alkenes or methyl ketones in the gas phase are indeed observed, in agreement with the proposed mechanism. Such reactivity is also maintained by several fragment ions of [RuL₃]⁺, indicating the preserved thiyl diradical core structure is responsible for the addition reaction. The thiyl radical nature of [RuL₃]⁺ was further verified by the ion/molecule reaction of [RuL₃]⁺ with dimethyl disulfide, in which the characteristic CH₃S? transfer occurs, both at atmospheric pressure and also at low pressure (~mTorr). These results provide, for the first time, clear mass spectrometric evidence of the radical nature of [RuL₃]⁺ (i.e., the distonic ion structure of [RuL₃]⁺), arising from the oxidation of non-innocent thiolate ligands of the complex [PPN]⁺[RuL₃]^-. Similar thiolate complexes, including ReL₃ and NiL₂, were also examined. Although reactions of oxidized ReL₃ or NiL₂ with CH₃SSCH₃ take place at atmospheric pressure, the corresponding reaction did not occur in vacuum. Consistent with these data, the addition of ethylene was not observed either, indicating lower reactivities of [ReL₃]⁺ and [NiL₂]⁺ in comparison to [RuL₃]⁺.      

Synthesis, characterization and interaction with DNA of ruthenium(II) mixed-ligand complexes containing pyridino[3,2-f] [1,7]phenanthroline

Summary A series of new complexes [RuL₂(pdphen)]²⁺, where pdphen is the planar ligand pyridino[3,2-f] [1,7]phenanthroline and L = 2,2-bipyridine, phenanthroline, 2,9-dimethylphenanthroline or 5-nitrophenanthroline, were prepared and characterized. The binding of [RuL₂-(pdphen)] ²⁺ to calf thymus DNA was investigated using absorption, fluorescence and circular dichroism (c.d.) spectroscopies. All of the complexes show absorption hypochromicity associated with binding to calf thymus DNA. [Ru(bipy)₂pdphen]²⁺ and [Ru(phen)₂pdphen]²⁺ also show fluorescence intensities and excited state life-time increases. The c.d. spectra of dialyzates from solutions of racemic complexes versus calf thymus DNA indicate enantioselectivity associated with binding to DNA.     

Multiply charged ions of ruthenium(II), rhodium(III) and cobalt(III) complexes in electrospray ionization mass spectrometry

Multiply charged ions from electrospray ionization (ESI) were observed for ruthenium-bidentate ligand complexes, such as [RuL₂B]X₂ and [(RuL₂)₂B]X₄, where L is 2,2′-bipyridine, B are tetradentate ligands of 2,2′-bis(2′-pyridyl)bibenzimidazole and 2,6-bis(2′-pyridyl)benzodiimidazole, bidentate ligand of 2-(2′-pyridyl)benzimidazole and related compounds and X is CIO₄^- or CI^-. ESI mass spectra showed a simple mass pattern for easy structural assignment and detecting impurities. The mass spectra for binuclear complexes provide a charge state distribution ranging from 4+ to 2+ for Ru(II)—Ru(II) compounds and 5+ to 2+ for Ru(II)—Rh(III) compounds. It was found that different multiply charged ions are generated by loss of counterions and by protonation/deprotonation at the proton site of ligands B. The abundances of these ions are qualitatively explained in terms of the acidity of metal complexes depending on the bridging ligand structures and the charge of the metal ions. Ions produced by removal of ligands were hardly observed.     

Photophysical Properties of Rufloxacin in Neutral Aqueous Solution

The photophysical properties of rufloxacin, 9-fluoro-2_r3-dihydro-10-(4-methyl-l-pyrazinyl)-7-oxo-7-H-pyri-do[l,2,3-de]-l,4-benzothiazin-6-carboxylic acid, a fluoroquinolone antibacterial drug exhibiting photosensitizing action toward biological substrates, were studied in aqueous solutions at neutral pH. The lowest excited electronic states of the zwitterion were characterized by both experimental techniques and theoretical methods. Steady-state and time-resolved emission, triplet-state absorption and singlet oxygen production were investigated. The results indicate that the lowest excited singlet is a fluorescent, relatively long-lived state (φ_r= 0.075, T_r? 4.5 ns) with an efficient intersystem crossing to the triplet manifold (φ_isc? 0-⁷)- The lowest triplet is a long-lived state (T_T? 10 μs at 295 K in 0.01 M phosphate buffer), with properties that make it a good candidate for being the precursor of the photodecarboxylation of the drug. It is quenched by oxygen at a rate of 1.7 times 10⁹M^-1 s-¹ and singlet oxygen is formed with a quantum yield of 0.32 in air-saturated solutions.     

Integrated Systems for Water Cleavage by Visible Light; Sensitization of TiO2 Particles by Surface Derivatization with Ruthenium Complexes

Irradiation of acidic (pH 2) solutions of RuL₃²⁺ 2Cl^? (L = diisopropyl 2,2′-bipyridine-4,4′ -dicarboxylate) in the presence of TiO₂ at 100°C leads to the loss of one bipyridyl ligand and the chemical fixation of RuL₂ at the surface of teh TiO₂ particles through formation of Ru-O-Ti bonds. These surface complexes are very stable and shift the absorption onset of TiO₂ beyond 600 mm. Efficient sensitization H₂-generation is achieved with this system beginning in the wave length domain between 590 and 665 nm. Preliminary water cleavage experiments with bifunctional TiO₂/Pt/RuO₂ redox catalyst are reported.     

Emission spectroscopy and excited-state dynamics of chromyl-chloride vapor

A tunable dye laser has been used to excite single vibronic features in the low-pressure vapor of CrO₂Cl₂. The fluorescence spectrum, fluorescence excitation spectrum and time-resolved fluorescence decay are discussed. It is shown that the active ν′₄ and ν″₄ modes are the same frequency in the gas phase, thus collapsing the sequence congestion normally observed in gas-phase spectra. This degeneracy makes impossible the excitation of single vibronic levels. It is shown that the fluorescence lifetime of the excited state in all except the vibrationally cold level is severely shortened by unimolecular radiationless decay. This radiationless rate is strongly dependent upon the partitioning of energy into various excited-state modes. The radiative lifetime of the vibrationally cold excited state is (1.34 ± 0.08) μs and the apparent bimolecular quenching rate is (5.9 ± 0.2) × 10^?10 cm³/molecules. No evidence of emission from the lowest-energy excited electronic state recently reported by Spoliti [J. Mol. Spectrosc. 52 (1973) 146] is observed.     

Photophysical Properties and Heterogeneous Photoredox Catalytic Activities of Ru(bpy)3@InBTB Metal–Organic Framework (MOF)

Metal–organic frameworks (MOFs) with negatively charged frameworks are suitable for selectively encapsulating cationic guest ions via a cation-exchange process. Encapsulating photoactive [RuL₃]²⁺ polypyridine complexes into the preorganized mesoscale channels of a MOF is a good method for stabilizing the excited states of the complexes. Three new RuL₃@InBTB MOFs were prepared by encapsulating cationic [Ru(bpy)₃]²⁺ (bpy=2,2′-bipyridine), [Ru(phen)₃]²⁺ (phen=1,10-phenanthroline), and [Ru(bpz)₃]²⁺ (bpz=2,2′-bipyrazine) into the mesopores of a three-dimensional (3D) InBTB MOF (H₃BTB=1,3,5-benzenetribenzoic acid). The photophysical properties of the resulting materials were investigated by photoluminescence (PL) analysis. The photoredox catalytic activities were also investigated for the aza-Henry reaction, hydrogenation of dimethyl maleate, and decomposition of methyl orange under visible light irradiation at room temperature. RuL₃@InBTB MOFs were found to be very stable and highly recyclable photoredox catalytic systems.     

Extending Metal‐to‐Polyoxometalate Charge Transfer Lifetimes: The Effect of Heterometal Location

In an effort to develop robust molecular sensitizers for solar fuel production, the electronic structure and photodynamics of transition‐metal‐substituted polyoxometalates (POMs), a novel class of compound in this context, was examined. Experimental and computational techniques including femtosecond (fs) transient absorption spectroscopy have been used to study the cobalt‐containing Keggin POMs, [Co^IIW₁₂O₄₀]^6? ( 1 a ), [Co^IIIW₁₂O₄₀]^5? ( 2 a ), [SiCo^II(H₂O)W₁₁O₃₉]^6? ( 3 a ), and [SiCo^III(H₂O)W₁₁O₃₉]^5? ( 4 a ), finding the longest lived charge transfer excited state so far observed in a POM and elucidating the electronic structures and excited‐state dynamics of these compounds at an unprecedented level. All species exhibit a bi‐exponential decay in which early dynamic processes with time constants in the fs domain yield longer lived excited states which decay with time constants in the ps to ns domain. The initially formed states of 1 a and 3 a are considered to result from metal‐to‐polyoxometalate charge transfer (MPCT) from Co^II to W, while the longer‐lived excited state of 1 a is tentatively assigned to a localized intermediate MPCT state. The excited state formed by the tetrahedral cobalt(II) centered heteropolyanion ( 1 a ) is far longer‐lived (τ=420 ps in H₂O; τ=1700 ps in MeCN) than that of 3 a (τ=1.3 ps), in which the single Co^II atom is located in a pseudo‐octahedral addendum site. Short‐lived states are observed for the two Co^III‐containing heteropolyanions 2 a (τ=4.4 ps) and 4 a (τ=6.3 ps) and assigned solely to O→Co^III charge transfer. The dramatically extended lifetime for 1 a versus 3 a is ascribed to a structural change permitted by the coordinatively flexible central site, weak orbital overlap of the central Co with the polytungstate framework, and putative transient valence trapping of the excited electron on a single W atom, a phenomenon not noted previously in POMs.     

State‐state transitions for CCl2(X1A1, A1B1, a3B1) radical and collisional quenching of CCl2(A1B1 and a3B1) by O2, N2, NO,N2O,NH3, and various aminated molecules

CCl₂ free radicals were produced by a pulsed dc discharge of CCl₄ in Ar. Ground electronic state CCl₂(X) radicals were electronically excited to the A¹B₁ (0,4,0) vibronic state with an Nd:YAG laser pumped dye laser at 541.52 nm. Experimental quenching data of excited CCl₂(A¹B₁ and a³B₁) by O₂, N₂, NO, N₂O, NH₃, NH(CH₃)₂, NH(C₂H₅)₂, and N(C₂H₅)₃ molecules were obtained by observing the time‐resolved total fluorescence signal of the excited CCl₂ radical in a cell, which showed a superposition of two exponential decay components under the presence of quencher. The quenching rate constants k_A of CCl₂(A) state and k_a of CCl₂(a) state were derived by analyzing the experimental data according to a proposed three‐level model to deal with the CCl₂(X¹A₁, A¹B₁, a³B₁) system. The formation cross sections of complexes of electronically excited CCl₂ radicals with O₂, N₂, NO, N₂O, NH₃, and aminated molecules were calculated by means of a collision‐complex model. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 351–356, 2002     

Spectral Properties of Ruthenium(II) Mixed-Ligands Complexes with 2,2'-Bipyridyl and Phosphines

Spectral-kinetic luminescence characteristics of the complexes cis-[Ru(bpy)(dppe)X2], cis- [Ru(bpy)2(PPh₃)X](BF₄) and cis-[Ru(bpy)₂X₂] [bpy = 2,2'-bipyridyl, dppe = 1,2-bis(diphenylphosphino)ethane, PPh₃ is triphenylphosphine, X = NO₂ ^- and CN^-] in the ethanol-methanol 4:1 mixtures and adsorbed on the oxide SiO₂ or porous polyacrylonitrile polymer surface were studied. Luminescence and luminescence exitation spectra were registered at 77 and 293 K in 230-750 nm range and the luminescence decay time was measured. Introduction of phosphine ligands to the ruthenium(II) bipyridyl complexes inner sphere leads to rise in singlet and triplet state energy at the charge transfer from Ru(II) to 2,2'-bipyridyl in the series [Ru(bpy)₂X₂] < Ru(bpy)₂(PPh₃)X](BF₄) < [Ru(bpy)(dppe)X₂]. The complex adsorption on SiO₂ or polyacrylonitrile surface affects noticeably the luminescence spectro-kinetic characteristics.     

Steady‐State and Pseudo‐Steady‐State Photocrystallographic Studies on Linkage Isomers of [Ni(Et4dien)(η2‐O,ON)(η1‐NO2)]: Identification of a New Linkage Isomer

At temperatures below 150 K, the photoactivated metastable endo‐nitrito linkage isomer [Ni(Et₄dien)(η²‐O,ON)(η¹‐ONO)] (Et₄dien=N,N,N′,N′‐tetraethyldiethylenetriamine) can be generated with 100 % conversion from the ground state nitro‐(η¹‐NO₂) isomer on irradiation with 500 nm light, in the single crystal by steady‐state photocrystallographic techniques. Kinetic studies show the system is no longer metastable above 150 K, decaying back to the ground state nitro‐(η¹‐NO₂) arrangement over several hours at 150 K. Variable‐temperature kinetic measurements in the range of 150–160 K show that the rate of endo‐nitrito decay is highly dependent on temperature, and an activation energy of E_act=+48.6(4) kJ mol^?1 is calculated for the decay process. Pseudo‐steady‐state experiments, where the crystal is continually pumped by the light source for the duration of the X‐ray experiment, show the production of a previously unobserved, exo‐nitrito‐(η¹‐ONO) linkage isomer only at temperatures close to the metastable limit (ca. 140–190 K). This exo isomer is considered to be a transient excited‐state species, as it is only observed in data collected by pseudo‐steady‐state methods.     

Excited State Dynamics of Isocyano Rhenium(I) Phenanthroline Complexes from Time-Resolved Spectroscopy

The photophysical processes in a series of isocyano Re(I) phenanthroline complexes {[Re(CNR)_n(CO)_4-n(phen)](PF₆); n=2, 3, 4, R=2,6-(ⁱPr)₂C₆H₃- or ^tBu- (n=2)} in acetonitrile have been studied by resonance Raman spectroscopy, transient resonance Raman spectroscopy, and femtosecond / nanosecond transient spectroscopy to elucidate the nature of their electronic transitions and emissive excited state(s). The kinetics of the intersystem crossing, vibrational relaxation and radiative decay of the metal-to-ligand charge transfer {MLCT [dπ(Re)→π*(phen)]} excited state have also been determined.     

Pseudorotational dynamics of H3+ and Li3+

The origin of the pseudoprecession phenomenon is investigated through a computational study of the time evolution of H₃⁺ and Li₃⁺ by electron nuclear dynamics theory. In particular, the pseudorotation of both molecules is shown to induce a spatial rotation, which in turn leads to Coriolis coupling of the two orthogonal nuclear shape deformation modes. This effect is rooted in an anisotropy of the molecular ground state potential energy surface that is caused by the interaction between the D_3h ground state and a twofold degenerate first excited state. Computations are performed for a variety of vibrational energies. In addition, the impact of the anharmonicity of the ground state potential surface on the shape deformation modes and the coupling between them is discussed. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Photophysical and electrochemical behavior of thin solid films based on a three-dimensional ruthenium complex network

RuL ₃ ²⁺ (L=2,2′-bipyridine-4,4′-diphosphonic acid) thin solid films were fabricated by three-dimensional linking between the phosphonic acid substituents of L and Zr(O)Cl₂. The RuL₃ chromophores in the films are electronically independent of each other in the ground state and give emission spectra essentially identical to that of RuL ₃ ²⁺ in solution, although the emission lifetime is much shorter. The films are electrochemically active, showing pseudo-reversible oxidation behavior in cyclic voltammetry. A preliminary attempt has been made to apply these films to photoelectrochemical cells.     

Singlet-Oxygen (1Δg) Production by Ruthenium(II) complexes containing polyazaheterocyclic ligands in methanol and in water

In the context of our studies on ruthenium(II) complexes containing polyazaheterocyclic ligands, we have determined the rate constants of quenching by molecular oxygen (k_q) of the metal-to-ligand charge-transfer-excited state of a series of homoleptic [RuL₃] complexes (where L stands for 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2′-bipyrazine (bpz), 4,7-diphenyl-1,10-phenanthroline (dip), diphenyl-1,10-phenanthroline-4,7-disulfonate (dpds), and 1, 10-phenanthroline-5-octadecanamide (poda)) in H₂O and in MeOH. These compounds are singlet-oxygen (O₂(¹Δ_g)) sensitizers, and quantum yields of singlet-oxygen production (Ψ_Δ) in both solvents are also reported. Values of k_q and Ψ_Δ depend on the nature of the ligand L and on the solvent, Ψ_Δ values showing a large range of variation (0.2 to 1.0). In MeOH, the only pathway for quenching of the excited [RuL₃] complexes by molecular oxygen is energy transfer: the fraction of quenched excited states yielding singlet oxygen (?) is unity for all compounds in the series investigated. Changing from MeOH to H₂O has several remarkable effects: higher k_q and lower Ψ_Δ values are observed; ? drops to ca. 0.5 except for [Ru(bpz)₃]²⁺. In fact, [Ru(bpz)₃]²⁺ is by far the weakest reductant in the series and behaves differently from the other complexes, with lowest k_q and Ψ_Δ values and a ? equal to 1 in both solvents. Results are interpreted on the basis of the role played by charge-transfer interactions between the sensitizer excited state and molecular oxygen in the quenching mechanism. Ru^II Complexes based on the 4,7-diphenyl-1, 10-phenanthroline (dip) ligand are very efficient and stable singlet-oxygen sensitizers with Ψ_Δ values close to unity in air-saturated MeOH.     

Photoisomerization Mechanism of Ruthenium Sulfoxide Complexes: Role of the Metal‐Centered Excited State in the Bond Rupture and Bond Construction Processes

Phototriggered intramolecular isomerization in a series of ruthenium sulfoxide complexes, [Ru(L)(tpy)(DMSO)]ⁿ⁺ (where tpy=2,2’:6’,2’’‐terpyridine; DMSO=dimethyl sulfoxide; L=2,2’‐bipyridine (bpy), n=2; N,N,N’,N’‐tetramethylethylenediamine (tmen) n=2; picolinate (pic), n=1; acetylacetonate (acac), n=1; oxalate (ox), n=0; malonate (mal), n=0), was investigated theoretically. It is observed that the metal‐centered ligand field (³MC) state plays an important role in the excited state S→O isomerization of the coordinated DMSO ligand. If the population of ³MC_S state is thermally accessible and no ³MC_O can be populated from this state, photoisomerization will be turned off because the ³MC_S excited state is expected to lead to fast radiationless decay back to the original ¹GS_S ground state or photodecomposition along the Ru²⁺?S stretching coordinate. On the contrary, if the population of ³MC_S (or ³MC_O) state is inaccessible, photoinduced S→O isomerization can proceed adiabatically on the potential energy surface of the metal‐to‐ligand charge transfer excited states (³MLCT_S→³MLCT_O). It is hoped that these results can provide valuable information for the excited state isomerization in photochromic d⁶ transition‐metal complexes, which is both experimentally and intellectually challenging as a field of study.     

Effect of Protonation and Deprotonation on Electron Transfer Mediated Decay and Interatomic Coulombic Decay

Electronically excited atoms or molecules in an environment are often subject to interatomic/intermolecular Coulombic decay (ICD) and/or electron transfer mediated decay (ETMD) mechanisms. A few of the numerous variables that can impact these non-radiative decay mechanisms include bond distance, the number of nearby atoms or molecules, and the polarisation effect. In this paper, we have studied the effect of protonation and deprotonation on the ionization potential (IP), double ionization potential (DIP), and lifetime (or decay width) of the temporary bound state in these non-radiative decay processes. We have chosen LiH-NH₃ and LiH-H₂O as test systems. The equation of motion coupled cluster singles and doubles method augmented by complex absorbing potential (CAP-EOM-CCSD) has been used in calculating the energetic position of the decaying state and the system's decay rate. Deprotonation of LiH-NH₃/LiH-H₂O either from the metal center (LiH) or from ammonia/water lowers the IP and DIP compared to the neutral systems. In contrast, protonation increases these quantities compared to neutral systems. The protonation closes the inner valence state relaxation channels for ICD/ETMD. For example, the decay of the O-2s/N-2s state stops in protonated systems (LiH₂⁺-H₂O, LiH₂⁺-NH₃, and LiH-NH₄⁺). Our study also shows that the efficiency, i. e., the rate of ICD/ETMD, can be altered by protonation and deprotonation. It is expected to have implications for chemical and biological systems.     

Effect of Nonchromophoric Ligands on the Spectral Characteristics of Ruthenium(II) (2,2'-Bipyridine)diphosphine Complexes

The electronic absorption and luminescence spectra of the complexes cis-[Ru(bpy)(dppe)X₂] [bpy is 2,2'-bipyridine, dppe is 1,2-bis(diphenylphosphino)ethane] in 4 : 1 ethanol-methanol mixtures at 77 and 293 K were measured, and the luminescence decay times were determined. As the field strength of the nonchromophoric ligand X increases in the order I^- < Br^- < Cl^- < 1/2(CO₃ ^{2 -}) < NCS^- < NO₂ ^- < CN^-, the electronic transitions are blue-shifted, and the luminescence decay time becomes longer.     

(阳离子表面活性剂-I3)n缔合微粒体系的光谱特性及分析应用

在0.01 mol/L HCl介质中,I-3在350 nm处有一吸收峰;当十六烷基三甲基溴化铵(CTMAB)与I-3共存时体系呈红紫色,在550 nm处产生一新的吸收峰.CTMAB浓度CCTMAB在0.0～7.0×10-5 mol/L范围内符合比耳定律,回归方程为A550 nm =0.989×104 CCTMAB+0.0138,相关系数R为0.999 5,摩尔吸光系数ε为1.06×104 L/(mol·cm),据此建立了一种测定阳离子表面活性剂含量的分光光度新方法,并用于合成样品和新洁尔净样品中阳离子表面活性剂测定.共振散射光谱研究表明,CTMAB+与I-3可通过静电引力作用形成疏水性的CTMA-I3缔合物分子,并进一步聚集形成稳定的 (CTMA-I3)n缔合微粒.由于该缔合微粒在580 nm处产生共振散射效应,故体系呈红紫色.