Search

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]

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]

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.

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]

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]

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]

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]