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A series of Ru(II)-terpyridine complexes containing electron-donating bidentate ligands are able to effectively photodissociate nitrile ligands using red light. A spectroscopic investigation of these complexes reveal that they follow anti-energy gap law behavior, providing further evidence that population of 3LF excited states is not necessary for photoinduced nitrile dissociation. [ABSTRACT FROM AUTHOR]

Ruthenium polypyridine complexes comprising sulfoxide ligands show dramatic photochromic behavior based on phototriggered S→O and O→S isomerization. Quantum yields of isomerization can be large, indicating that the excited-state bond-breaking and bond-making reactions are efficient. Ultrafast transient absorption spectroscopy reveals both adiabatic and non-adiabatic isomerization mechanisms. Incorporation of these complexes within polymer matrices leads to macroscopic bending of the polymer in an example of a direct transduction of photonic energy to mechanical energy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: The background and achievements in the growing field of electron-transfer triggered sulfoxide isomerizations is reviewed. Starting with the original electrochemical investigations by Taube, followed by the seminal investigations by Deutsch and Meyer and concluding with the picosecond transient absorption measurements of the direct excited state S→O isomerization, this review highlights these important contributions to the field. The remarkable photochemistry exhibited by certain ruthenium sulfoxide complexes is contrasted with the more well-known medicinal chemistry of ruthenium-halo-sulfoxide complexes. This chemistry is also compared to the photochemistry of metal nitrosyl complexes. [Copyright &y& Elsevier]

The complexes [Ru(tpy)(bpy)(dmso)](OSO2CF3)2 and trans-[Ru(tpy)(pic)(dmso)](PF6) (tpy is 2,2′: 6′,2″-terpyridine, bpy is 2,2′-bipyridine, pic is 2-pyridinecarboxylate, and dmso is dimethyl sulfoxide) were investigated by picosecond transient absorption spectroscopy in order to monitor excited-state intramolecular S→O isomerization of the bound dmso ligand. For [Ru(tpy)(bpy)(dmso)]2+, global analysis of the spectra reveals changes that are fit by a biexponential decay with time constants of 2.4 ± 0.2 and 36 ± 0.2 ps. The first time constant is assigned to relaxation of the S-bonded ³MLCT excited state. The second time constant represents both excited-state relaxation to ground state and excited-state isomerization to form O-[Ru(tpy)(bpy)(dmso)]2+*. In conjunction with the S→O isomerization quantum yield (ΦS→O = 0.024), isomerization of [Ru(tpy)(bpy)(dmso)]2+ occurs with a time constant of 1.5 ns. For trans-[Ru(tpy)(pic)(dmso)]+, global analysis of the transient spectra reveals time constants of 3.6 ± 0.2 and 118 ± 2 ps associated with these two processes. In conjunction with the S→O isomerization quantum yield (ΦS→O = 0.25), isomerization of trans-[Ru(tpy)(pic)(dmso)]+ occurs with a time constant of 480 ps. In both cases, the thermally relaxed excited states are assigned as terpyridine-localized ³MLCT states. Electronic state diagrams are compiled employing these data as well as electrochemical, absorption, and emission data to describe the reactivity of these complexes. The data illustrate that rapid bond-breaking and bond-making reactions can occur from ³MLCT excited states formed from visible light irradiation. [ABSTRACT FROM AUTHOR]

Examines the synthesis of metal containing oligonucleotides using automated DNA synthesis techniques. Incorporation of metal complexes into DNA; Preparation of metal containing monomers; Action of oligonucleotides on the electronic property of ruthenium complex.

Reports on the synthesis and characterization of salts of the cationic silver(I) carbonyl complexes [Ag(CO)]+ and [Ag(CO)2]+. Carbon monoxide's irreversible binding with to silver.

Reports on the spectroscopy, electrochemistry and linkage isomerization in a family of [Ru(tpy)(L2)(dmso)[sup Z+] complexes. Importance of ancillary ligands in photochromic ruthenium-dmso complexes; Role of electron transfer in isomerization.

Reports on phototriggered Ruthenium-sulphur to ruthenium-oxygen and ruthenium-oxygen to ruthenium-sulphur intramolecular linkage isomerization in cis- and trans-[Ru(bpy)[sub 2](dmso)sub 2]][sup 2+]. Thermal reversion to the ground state in ionic liquid; Absorption spectra.

The S==O stretching mode in sulfoxides, having a frequency in the 950-1150 cm-1 range, is tested as a structural label via dual-frequency two-dimensional infrared (2DIR) spectroscopy. The properties of this structural reporter are studied in several compounds, including (4,4′-dimethyl-2,2′-bipyridyl)(o-methylsulfinylbenzoate) ruthenium II, [Ru(dmb)2(BzSO)]+, (RuBzSO), octylsulfinylpropionic acid (OSPA), and o- and p-methylsulfinyl-benzoic acid (oMSBA and pMSBA). The mode assignment in the fingerprint region for these compounds is made using a combination of density functional theory calculations and 2DIR and relaxation-assisted 2DIR (RA 2DIR) spectroscopies. The SO stretching mode frequency and IR intensity demonstrate substantial sensitivity to the molecular structure. Multiple cross peaks of the C==O and S==O stretching modes with modes in the fingerprint region (930-1450 cm-1) were recorded. The 2DIR and RA 2DIR spectra focusing at interactions of a high-frequency mode of a ligand with the modes in the fingerprint region provide a spectral fingerprint of a compound and help mode assignment in the often congested fingerprint region. The cross-peak amplitudes in oMSBA, pMSBA, and OSPA were compared with the theoretical predictions based on the computed values for the off-diagonal anharmonicities and a reasonable match is found. The SO stretching mode provides means for assigning other modes in the fingerprint region and constitutes a promising structural reporter for the 2DIR and RA 2DIR spectroscopy measurements. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) are advancing because of their superior external quantum efficiencies (EQEs) and color purity. Still, additional work is needed for blue PeLEDs to achieve the same benchmarks as the other visible colors. This study demonstrates an extremely efficient blue PeLED with a 488 nm peak emission, a maximum luminance of 8600 cd m−2, and a maximum EQE of 12.2% by incorporating the double‐sided ethane‐1,2‐diammonium bromide (EDBr2) ligand salt along with the long‐chain ligand methylphenylammonium chloride (MeCl). The EDBr2 successfully improves the interaction between 2D perovskite layers by reducing the weak van der Waals interaction and creating a Dion–Jacobson (DJ) structure. Whereas the pristine sample (without EDBr2) is inhibited by small stacking number (n) 2D phases with nonradiative recombination regions that diminish the PeLED performance, adding EDBr2 successfully enables better energy transfer from small n phases to larger n phases. As evidenced by photoluminescence (PL), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterization, EDBr2 improves the morphology by reduction of pinholes and passivation of defects, subsequently improving the efficiencies and operational lifetimes of quasi‐2D blue PeLEDs. [ABSTRACT FROM AUTHOR]

Discusses the spectroscopy and electrochemistry of halo-ruthenium(sulfoxide) complexes. Structure of mer[RuCl3(dimethylsulfoxide)(tmen0]; Exhibition of two reversible electron waves by the acetonitrile mer [RuCl3(dmso)(tmen)] solution; Indication of a pi-back-bonding between Ru(III) or Ru(II) and dmso in the solution.

Reports on the production of homoleptic copper carbonyl cations by carbon monoxide with the exposure of crystalline CuAsF6 to less than 1 atmosphere. Characterization with IR and Raman spectroscopy; Compounds as representatives of the first examples of isolable polycarbonyls of copper(I).

Conspectus: Molecular photochromic compounds are those that interconvert between two isomeric forms with light. The two isomeric forms display distinct electronic and molecular structures and must not be in equilibrium with one another. These light-activated molecular switch compounds have found wide application in areas of study ranging from chemical biology to materials science, where conversion from one isomeric form to another by light prompts a response in the environment (e.g., protein or polymeric material). Certain ruthenium and osmium polypyridine sulfoxide complexes are photochromic. The mode of action is a phototriggered isomerization of the sulfoxide from S- to O-bonded. The change in ligation drastically alters both the spectroscopic and electrochemical properties of the metal complex. Our laboratory has pioneered the preparation and study of these complexes. In particular, we have applied femtosecond pump-probe spectroscopy to reveal excited state details of the isomerization mechanism. The data from numerous complexes allowed us to predict that the isomerization was nonadiabatic in nature, defined as occurring from a S-bonded triplet excited state (primarily metal-to-ligand charge transfer in character) to an O-bonded singlet ground state potential energy surface. This prediction was corroborated by high-level density functional theory calculations. An intriguing aspect of this reactivity is the coupling of nuclear motion to the electronic wave function and how this coupling affects motions productive for isomerization. In an effort to learn more about this coupling, we designed a project to examine phototriggered isomerization in bis-sulfoxide complexes. The goal of these studies was to determine whether certain complexes could be designed in which a single photon excitation event would prompt two sulfoxide isomerizations. We employed chelating sulfoxides in this study and found that both the nature of the chelate ring and the R group on the sulfoxide affect the photochemical reactivity. For example, this reactivity may be tuned such that two sulfoxide ligands isomerize sequentially following two successive excitations or that two sulfoxide ligands isomerize following a single excitation. This Account explains our understanding to date of this photochemistry. [ABSTRACT FROM AUTHOR]

Photochromic compounds efficiently transduce photonic energy to potential energy for excited-state bond-breaking and bond-forming reactions. A critical feature of this reaction is the nature of the electronic excited-state potential energy surface and how this surface facilitates large nuclear displacements and rearrangements. We have prepared two photochromic ruthenium sulfoxide complexes that feature two isomerization reactions following absorption of a single photon. We show by femtosecond transient absorption spectroscopy that this reaction is complete within a few hundred picoseconds and suggest that isomerization occurs along a conical intersection seam formed by the ground-state and excited-state potential energy surfaces. [ABSTRACT FROM AUTHOR]

We report the preparation and spectroscopic properties of [Os(bpy)2(pySO)]2+ and [Os(bpy)2(pySOCF3)]2+, where bpy is 2,2′-bipyridine, pySO is 2-(propane-2-sulfinylmethyl)pyridine, and pySOCF3 is 2-[(trifluoroethylsulfinyl)methyl]pyridine. The charge-transfer absorption spectra of [Os(bpy)2(pySO)]2+ and [Os(bpy)2(pySOCF3)]2+ are 378 and 367 nm, respectively. Charge-transfer excitation of [Os(bpy)2(pySOCF3)]2+ shows substantial changes in the UV/Vis spectrum with a shift in the lowest energy absorption maximum from 367 to 415 nm, which is consistent with phototriggered S→O isomerization. Irradiation of [Os(bpy)2(pySO)]2+ shows no evidence of isomerization. Cyclic voltammograms of [Os(bpy)2(pySO)]2+ and [Os(bpy)2(pySOCF3)]2+ feature reversible one-electron couples that are ascribed to Os3+/2+ reduction potentials ( E°′) at 1.01 V (vs Ag/AgCl; $\tilde {\nu}$ = 0.1 V/s; CH3CN; 0.1 M TBAPF6) and 1.17 V, respectively. Femtosecond to nanosecond transient absorption spectra for [Os(bpy)2(pySOCF3)]2+ are reported. For [Os(bpy)2(pySOCF3)]2+, fits of data obtained at 370 nm yield lifetimes of 0.20 (±0.02) and 19.7 (±8) ps, whereas for [Os(bpy)2(pySO)]2+ lifetimes of 0.47 (±0.2) and 12.7 (±11) ps are obtained at 378 nm. These lifetimes are ascribed to the formation of a 3MLCT state and solvent reorganization, respectively. Excited state lifetimes of 331(±4) and 348 (±25) ns are found for [Os(bpy)2(pySO)]2+ and [Os(bpy)2(pySOCF3)]2+, respectively. The time constant for isomerization is 213 μs for [Os(bpy)2(pySOCF3)]2+. Transient absorption spectra reveal an excited state sulfoxide to Os3+ transition. The electrochemical and spectroscopic data can be combined to yield electronic state diagrams for [Os(bpy)2(pySO)]2+ and [Os(bpy)2(pySOCF3)]2+. [ABSTRACT FROM AUTHOR]

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 0-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 0-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 fem to second 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-Iigand and S=0 vibrational modes, which are intrinsically involved in the isomerization pathway. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical and photochemical studies of a photochromic complex with a chelating sulfoxide are reported. Electrochemical data do not support evidence for isomerization following electrochemical oxidation. However, irradiation of solutions containing [Ru(bpy)2(PhNSO)](PF6)2 (bpy is 2,2′-bipyridine, PhNSO is N-benzylidine-2-(ethylsulfinyl)ethanamine) demonstrate excited state S→O isomerization. The S-bonded absorption maximum is 382nm, while the O-bonded isomer features absorption maxima at 360 and 486nm. The quantum yield of isomerization is 0.033 and the S-bonded isomer is emissive at low temperature (77K). These data and an electronic structural model explaining this reactivity are introduced. [Copyright &y& Elsevier]

The photochromic compounds trans- and cis-[Ru(tpy)(Mepic)(dmso)](OSO2CF3) (2 and 3, respectively; tpy is 2,2′: 6′,2″-terpyridine; Mepic is 6-methyl-2-pyridinecarboxylate; dmso is dimethyl sulfoxide) and cis-[Ru(tpy)(Brpic)(dmso)]- (PF6) (4; Brpic is 6-bromo-2-pyridinecarboxylate) were prepared and characterized by single-crystal X-ray crystallography, electrochemistry, NMR, IR, and UV-vis spectroscopy. The geometry labels refer to the relationship between the carboxylate oxygen of the picolinate ligand and dmso. Electrochemical studies reveal that only the trans isomer shows S-to-O isomerization following oxidation of Ru(ll) and O-to-S isomerization following reduction of Ru(lll). The cis isomers of both complexes feature reversible one-electron Ru(lll/ll) couples. All complexes undergo phototriggered S-to-O isomerization following MLCT (metal-to-ligand charge transfer) excitation with quantum yields (ΦS→O) of 0.79 (2), 0.011 (3), and 0.014 (4). The methyl group in 2 promotes isomerization by hindering rotation of the dmso ligand about the Ru-S bond. Computational results support this role for the methyl group. Relative energy calculations show that the barrier to rotation is approximately 8 kcal mol-1. These results suggest that rotation is an important vibration for isomerization in photochromic ruthenium-dmso complexes. [ABSTRACT FROM AUTHOR]

Compounds of the type [Ru(tpy)(L2)(dmso))2+ (tpy is 2,2′:6′,2″-terpyridine; L2 can be 2,2′-bipyridine (bpy), N,N,N′,N′-tetramethylethylenediamine (tmen), 2-pyridine carboxylate (pic), acetylacetonate (acac), malonate (mal), or oxalate (ox)) have been studied by X-ray crystallography, electrochemistry, NMR, IR, and UV-vis spectroscopy. When L2 is bpy, tmen, or pic, the dmso ligand can be intramolecularly isomerized either electrochemically or photochemically. lsomerization is not observed when L2 is acac, mal, or ox. Isomerization results in a drastic change in the absorption spectrum, as well as in the voltammetry. Absorption maxima shift by 3470 (419-490 nm), 4775 (421-527 nm), and 4440 cm-1 (429-530 nm) for the bpy, pic, and tmen complexes, respectively. Reduction potentials for S-bonded and O-bonded complexes differ by 0.57, 0.75, and 0.62 V for the bpy, pic, and tmen complexes, respectively. Quantum yields of isomerization (ϕS→O) were determined for the bpy (0.024 ± 1), pic (0.25 ± 1), and tmen (0.007 ± 1) complexes. In comparison of these data to photosubstitution quantum yields, it appears that the isomerization mechanism does not involve the ligand field states. This result is surprising given the importance of these states in the photochemistry of ruthenium and osmium polypyridine complexes. These results and details of the mechanism are discussed. [ABSTRACT FROM AUTHOR]

Transient absorption data of [FeII(tpy)(CN)3]− reveals spectroscopic signatures indicative of 3MLCT with a ∼10 ps kinetic component. These data are supported by DFT and TD-DFT calculations, which show that excited state ordering is responsive to the number of cyanide ligands on the complex. [ABSTRACT FROM AUTHOR]

We report the structure, spectroscopy, and electrochemistry of cis-[Os(bpy)2(DMSO)2](OTf)2, where bpy is 2,2′-bipyridine, DMSO is dimethyl sulfoxide, and OTf is trifluoromethanesulfonate. Electrochemical measurements are consistent with S-to-O isomerization following the oxidation of Os2+ (1.8 V vs Ag/AgCl). Visible irradiation of the metal-to-ligand charge-transfer transition (355 nm) of [Os(bpy)2(DMSO)2]2+ in the solid state and solution yields an emissive S-bonded excited state and S-to-O excited-state isomerization on a subnanosecond time scale. These results and a comparison to the nonphotoactive [Os(bpy)2Cl(DMSO)]+ are discussed. [ABSTRACT FROM AUTHOR]

Lanthanide ion (LnIII) complexes, [Ln(3Tcbx)2]3+ (LnIII=YbIII, NdIII, ErIII) are isolated with a new pyridine‐bis(carboxamide)‐based ligand with a 2,2′:5′,2′′‐terthiophene pendant (3TCbx), and their resulting photophysical properties are explored. Upon excitation of the complexes at 490 nm, only LnIII emission is observed with efficiencies of 0.29 % at 976 nm for LnIII=YbIII and 0.16 % at 1053 nm for LnIII=NdIII. ErIII emission is observed but weak. Upon excitation at 400 nm, concurrent 1O2 formation is seen, with efficiencies of 11 % for the YbIII and NdIII complexes and 13 % for the ErIII complex. Owing to the concurrent generation of 1O2, as expected, the efficiency of metal‐centered emission decreases to 0.02 % for YbIII and 0.05 % for NdIII. The ability to control 1O2 generation through the excitation wavelength indicates that the incorporation of 2,2′:5′,2′′‐terthiophene results in access to multiple sensitization pathways. These energy pathways are unraveled through transient absorption spectroscopy. [ABSTRACT FROM AUTHOR]

A new pyridine-bis(carboxamide)-based ligand with a bithiophene pendant, 2Tcbx, was synthesized. Its lanthanide ion (LnIII) complexes, [Ln(2Tcbx)2]3+, were isolated and their photophysical properties were explored. Upon excitation at 360 nm, these complexes display emission in the near-infrared (NIR) with efficiencies of 0.69% for LnIII = YbIII, 0.20% for LnIII = NdIII, and 0.01% for LnIII = ErIII, respectively. Concurrent 1O2 formation was seen for all complexes, with efficiencies of 19% for the YbIII complex, 25% for the NdIII complex, and 9% for the ErIII complex. When exciting at a longer wavelength, 435 nm, only LnIII emission was observed and larger efficiencies of LnIII-centered emission were obtained. The lack of 1O2 generation indicates that energy pathways involving different ligand conformations, which were investigated by transient absorption spectroscopy, are involved in the sensitization process, and enable the wavelength-dependent generation of 1O2. [ABSTRACT FROM AUTHOR]

We report the synthesis, characterization, and detailed comparison of a series of novel Pt-bisacetylide containing conjugated small molecules possessing an unconventional "roller-wheel" shaped structure that is distinctly different from the "dumbbell" designs in traditional Pt-bisacetylide containing conjugated polymers and small molecules. The relationships between the chemical nature and length of the "rollers" and the electronic and physical properties of the materials are carefully studied by steady-state spectroscopy, cyclic voltammetry, differential scanning calorimetry, singlecrystal X-ray diffraction, transient absorption spectroscopy, theoretical calculation, and device application. It was revealed that if the roller are long enough, these molecules can "slip-stack" in the solid state, leading to high crystallinity and charge mobility. Organic solar cells were fabricated and showed power conversion efficiencies up to 5.9%, out-performing all existing Pt-containing materials. The device performance was also found to be sensitive to optimization conditions and blend morphologies, which are a result of the intricate interplay among materials crystallinity, phase separation, and the relative positions of the lowest singlet and triplet excited states. [ABSTRACT FROM AUTHOR]

Iron(II)-to-titanium(IV) metal-to-metal-charge transfer (MMCT) is important in the photosensitization of TiO2 by ferrocyanide, charge transfer in solid-state metal-oxide photocatalysts, and has been invoked to explain the blue color of sapphire, blue kyanite, and some lunar material. Herein, a series of complexes with alkynyl linkages between ferrocene (Fc) and TiIV has been prepared and characterized by UV-vis spectroscopy and electrochemistry. Complexes with two ferrocene substituents include Cp2Ti(C2Fc)2, Cp*2Ti(C2Fc)2, and Cp2Ti(C4Fc)2. Complexes with a single ferrocene utilize a titanocene with a trimethylsilyl derivatized Cp ring, TMSCp, and comprise the complexes TMSCp2Ti(C2Fc)(C2R), where R = C6H5, p-C6H4CF3, and CF3. The complexes are compared to Cp2Ti(C2Ph)2, which lacks the second metal. Cyclic voltammetry for all complexes reveals a reversible TiIV/III reduction wave and an FeII/III oxidation that is irreversible for all complexes except TMSCp2Ti(C2Fc)(C2CF3). All of the complexes with both Fc and Ti show an intense absorption (4000 M-1cm-1 < ε < 8000 M-1cm-1) between 540 and 630 nm that is absent in complexes lacking a ferrocene donor. The energy of the absorption tracks with the difference between the TiIV/III and FeIII/II reduction potentials, shifting to lower energy as the difference in potentials decreases. Reorganization energies, λ, have been determined using band shape analysis (2600 cm-1 < λ < 5300 cm-1) and are in the range observed for other donor-acceptor complexes that have a ferrocene donor. Marcus-Hush-type analysis of the electrochemical and spectroscopic data are consistent with the assignment of the low-energy absorption as a MMCT band. TD-DFT analysis also supports this assignment. Solvatochromism is apparent for the MMCT band of all complexes, there being a bathochromic shift upon increasing polarizability of the solvent. The magnitude of the shift is dependent on both the electron density at TiIV and the identity of the linker between the titanocene and the Fc. Complexes with a MMCT are photochemically stable, whereas Cp2Ti(C2Ph)2 rapidly decomposes upon photolysis. [ABSTRACT FROM AUTHOR]

Irradiation of [Ru(bpy)2(bpSOp)](PF6)2 (where bpy is 2,2'-bipyridine and bpSOp is 1,3-bis(phenylsulfinyl)-propane) results in the formation of two new isomers, namely the S,O- and O,O-bonded species. The crystal structure of the bis-thioether and bis-sulfoxide complexes are reported. NMR spectroscopy of the bis-thioether complex in solution is consistent with the molecular structure determined by diffraction methods. Further, NMR spectroscopy of the bis-sulfoxide complex reveals two conformers in solution, one that is consistent with the solid state structure and a second conformer showing distortion in the aliphatic portion of the chelate ring. Time-resolved visible absorption spectroscopy reveals isomerization time constants of 91 ps in dichloroethane (DCE) and 229 ps in propylene carbonate (PC). Aggregate isomerization quantum yields of 0.57 and 0.42 have been determined in DCE and in PC, respectively. The kinetics of the thermal reversion from the O,O- to S,O-bonded isomer are strongly solvent dependent, occurring with rates of 2.41 × 10-3 and 4.39 × 10-5 s-1 in DCE, and 4.68 × 10-4 and 9.79 × 10-6 s-1 in PC. The two kinetic components are assigned to the two isomers identified in solution. [ABSTRACT FROM AUTHOR]

We present the synthesis and characterization of a series of four fluorescent Sn(IV) Schiff base complexes, which also possess long-lived triplet excited states. The complexes absorb visible light (λmax = 420 to 462 nm) and the optical properties are easily tunable without laborious synthetic elaboration. The triplet excited states are not luminescent, but can be observed and followed using nanosecond transient absorption spectroscopy. The lifetimes of the triplet excited states are on the order of 500 µs-10 ms in PMMA matrices. The triplet state energies were estimated via energy transfer reactions with a series of organic triplet acceptors. In addition, the photoexcited complexes react with electron donors and acceptors in solution. These results demonstrate the potential for the development of photosensitizers based on main group elements with high spin orbit coupling constants. [ABSTRACT FROM AUTHOR]

The complexes [Ru(bpy)2(pyESO)](PF6)2 and [Os(bpy)2(pyESO)](PF6)2, in which bpy is 2,2′-bipyridine and pyESO is 2-((isopropylsulfinyl)ethyl)pyridine, were prepared and studied by 1H NMR, UV-visible and ultrafast transient absorption spectroscopy, as well as by electrochemical methods. Crystals suitable for X-ray structural analysis were grown for [Ru(bpy)2(pyESO)](PF6)2. Cyclic voltammograms of both complexes provide evidence for S→O and O→S isomerization as these voltammograms are described by an ECEC (electrochemical-chemical electrochemical-chemical) mechanism in which isomerization follows Ru2+ oxidation and Ru3+ reduction. The S- and O-bonded Ru3+/2+ couples appear at 1.30 and 0.76 V versus Ag/AgCl in propylene carbonate. For [Os(bpy)2(pyESO)](PF6)2, these couples appear at 0.97 and 0.32 V versus Ag/AgCl in acetonitrile, respectively. Charge-transfer excitation of [Ru(bpy)2(pyESO)](PF6)2 results in a significant change in the absorption spectrum. The S-bonded isomer of [Ru(bpy)2(pyESO)]2+ features a lowest energy absorption maximum at 390 nm and the O-bonded isomer absorbs at 480 nm. The quantum yield of isomerization in [Ru(bpy)2(pyESO)]2+ was found to be 0.58 in propylene carbonate and 0.86 in dichloroethane solution. Femtosecond transient absorption spectroscopic measurements were collected for both complexes, revealing time constants of isomerizations of 81 ps (propylene carbonate) and 47 ps (dichloroethane) in [Ru(bpy)2(pyESO)]2+. These data and a model for the isomerizing complex are presented. A striking conclusion from this analysis is that expansion of the chelate ring by a single methylene leads to an increase in the isomerization time constant by nearly two orders of magnitude. [ABSTRACT FROM AUTHOR]

The complex [Ru(bpy)2(bpSO)](PF6)2, where bpy is 2,2'-bipydine and bpSO is l,2-bis(phenylsulfinyl)ethane, exhibits three distinct isomers which are accessible upon metal-to-ligand charge-transfer (MLCT) irradiation. This complex and its parent, [Ru(bpy)2(bpte)](PF6)2, where bpte is 1,2-bis(phenylthio)ethane, have been synthesized and characterized by UV--visible spectroscopy, NMR, X-ray crystallography, and femtosecond transient absorption spectroscopy. A novel method of 2-color Pump-Repump-Probe spectroscopy has been employed to investigate all three isomers of the bis-sulfoxide complex This method allows for observation of the isomerization dynamics of sequential isomerizations of each sulfoxide from MLCT irradiation of the S,S-bonded complex to ultimately form the 0,0-bonded metastable complex. One-dimensional (l-D) and two-dimensional (2-D) (COSY, NOESY, and TOCSY) 'H NMR data show the thioether and ground state S,S-bonded sulfoxide complexes to be rigorously C2 symmetric and are consistent with the crystal structures. Transient absorption spectroscopy reveals that the S,S to S,0 isomerization occurs with an observed time constant of 56.8 (±7.4) ps. The S,0 to 0,0 isomerization time constant was found to be 59 (±4) ps by pump-repump-probe spectroscopy. The composite S,S- to 0,0-isomer quantum yield is 0.42. [ABSTRACT FROM AUTHOR]

This work illustrates the control of excited state energy transfer processes via variation of pH in transition metal complexes. In these systems a Ru(II) complex having two carboxylated bipyridyl ligands is covalently linked to pyrene via one of two different pyrene derivitized bipyridyl ligands. The energy of the Ru to carboxy-bipyridine ³MLCT state is pH dependent while the pyrene triplet energy remains unchanged with solution acidity. At pH 0 the ³MLCT state is the lowest energy state, and as the pH is raised and the carboxy-bipyridyl ligands are successively deprotonated, the energy of the ³MLCT state rises above that of the pyrene triplet, resulting in a significant increase in the lifetime of the observed emission. Detailed analysis of ultrafast and microsecond time-resolved excited state decays result in a description of excited state decay that involves initial equilibration of the ³MLCT and pyrene triplet states followed by relaxation to the ground state. The lifetime of excited state decay is defined by the position of the equilibrium, going from 2 μs at pH 0 to >10 μs at higher pH as the equilibrium favors the pyrene triplet. In addition, quenching of the excited state by dissolved oxygen exhibits a pH dependence that parallels that of the excited state lifetime. The results illustrate the utility of exploiting excited state equilibria of this type in the development of highly effective luminescent oxygen sensors. [ABSTRACT FROM AUTHOR]

Abstract: Complexes of the type [Ru(bpy)2(OSOBnR)](PF6) where bpy is 2,2′-bipyridine and OSOBnR is a 4-substituted benzylsulfinylbenzoate with R=NO2, F, Cl, H, CH3, CF3 and OCH3, have been prepared and investigated by 1H NMR spectroscopy, cyclic voltammetry and UV–vis spectroscopy. Despite the distance of the R group from ruthenium, the Ru3+/2+ reduction potential and charge transfer absorption maximum vary predictably with the electron withdrawing nature of the group. [ABSTRACT FROM AUTHOR]

We report the structure, electrochemistry, and isomerization kinetics for [Ru(bpy)(biq)(OSO)](PF6), where bpy is 2,2′-bipyridine, biq is 2,2′-biquinoline, and OSO is 2-methylsulfinylbenzoate. UV-visible and infrared data are suggestive of intramolecular S→O and O→S isomerization of the sulfoxide. Cyclic voltammetry reveals evidence for isomerization triggered by oxidation and reduction. Of particular note is the variation of the S→O isomerization rate constant in different solvents. The rates were found to be 3.2 (±0.4) s-1 in propylene carbonate, 0.80 (±0.03) s-1 in acetonitrile, and 0.26 (±0.01) s-1 in dichloromethane. [ABSTRACT FROM AUTHOR]

Abstract: The T box transcription antitermination riboswitch is one of the main regulatory mechanisms utilized by Gram-positive bacteria to regulate genes that are involved in amino acid metabolism. The details of the antitermination event, including the role that Mg2+ plays, in this riboswitch have not been completely elucidated. In these studies, details of the antitermination event were investigated utilizing 2-aminopurine to monitor structural changes of a model antiterminator RNA when it was bound to model tRNA. Based on the results of these fluorescence studies, the model tRNA binds the model antiterminator RNA via an induced-fit. This binding is enhanced by the presence of Mg2+, facilitating the complete base pairing of the model tRNA acceptor end with the complementary bases in the model antiterminator bulge. [Copyright &y& Elsevier]

The complexes [Ru(bpy)2(OS)](PF6) and [Ru(bpy)2(OSO)](PF6), where bpy is 2,2'-bipyridine, OS is 2-methylthio-benzoate, 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) x 10-4 s-1 and 3.1(1) x 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 ESo' = 0.86 V and EOo' = 0.49 V versus Ag/Ag+ for the S- and O-bonded Ru3+/2+ couples, respectively, in propylene carbonate. We found ks-o = 0.090(15) s-1 in propylene carbonate and ks-o = 0.11(3) s-1 in acetonitrile on RuIII, which is considerably slower than has been reported for other sulfoxide isometizations 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, isometization 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. [ABSTRACT FROM AUTHOR]

Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N'-phenylene-bis-(3,5-di-tert-butylsalicylideneimine); ZnLR) complexes. A structurally related family of ZnLR complexes (R = OMe, di-tBu, tBu, CI, 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 ZnLR were generally high (Φ~ 0.3) with sub-nanosecond fluorescence lifetimes. The fluorescence of ZnLR was quenched by nitroaromatic compounds by a mixture of static and dynamic pathways, reflecting the ZnLR ligand bulk and reduction potential. Steady-state Stern-Volmer plots were curved for ZnLR 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 ZnLR 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 ZnLR as sensors, as well as for potential photoinduced charge transfer chemistry. [ABSTRACT FROM AUTHOR]

We have prepared and characterized [Ru(bpy)2(OS)]+ (bpy = 2,2′-bipyridine; OS = 2-methylthiobenzoate) and the chelating sulfoxide S-[Ru(bpy)2(OSO)]+ (OSO = methylsulfonylbenzoate) by ¹H NMR (1-D and 2-D COSY), IR, UV-visible spectroscopy, electrochemistry, and X-ray crystallography. Many of the metrical and crystal parameters are nearly identical between the two structures. The sulfoxide is produced from m-cpba oxidation of the thioether. Photolysis of S-[Ru(bpy)2(OSO)]+ results in a dramatic shift in the metal-to-ligand charge-transfer (³MLCT) transition from 396 to 496 nm, with a new higher-energy ³MLCT transition appearing at 355 rim. Concomitant with this change, the Ru3+/2+ reduction potential shifts from 1.25 V vs Ag/AgCl to 0.9 V vs Ag/AgCl. These changes are ascribed to phototriggered excited-state isomerization of the sulfoxide from S- to O-bonded. Examination of the ¹H NMR spectra in a CD3OD solvent before, during, and after irradiation shows the presence of two O-bonded complexes that revert to the structurally characterized S-bonded ground state. This represents the first report of isomerization of a chelating sulfoxide in a photochromic Ru complex. [ABSTRACT FROM AUTHOR]

Carrier dynamics in monolayer MoS2 have been investigated using broadband femtosecond transient absorption spectroscopy (FTAS). A tunable pump pulse was used while a broadband probe pulse revealed ground and excited state carrier dynamics. Interestingly, for pump wavelengths both resonant and nonresonant with the A and B excitons, we observe a broad ground state bleach around 2.9 eV, with decay components similar to A and B. Associating this bleach with the band nesting region between K and G in the band structure indicates significant k-space delocalization and overlap among excitonic wave functions identified as A, B, C, and D. Comparison of time dynamics for all features in resonance and nonresonance excitation is consistent with this finding. [ABSTRACT FROM AUTHOR]