Tuning the excited-state properties of [M(SnR3)2(CO)2(alpha-diimine)] (M = Ru, Os; R = Me, Ph)

Water-Soluble Osmium Complexes Suitable for use in Luminescence-Based, Hydrogel-Supported Sensors

Osmium transition metal complexes are of particular interest in luminescence-based sensing applications because of their longer wavelength absorptions and emissions, relative to similar ruthenium and rhenium complexes, that allow for inexpensive excitation and minimize interferences from autofluorescence when the sensor is used in biological samples. Reported here are the photophysical properties of a series of water-soluble osmium complexes suitable for use in hydrogel-based sensors: [Os(bpy)₂(sulf-dpp)]Cl₂, [Os(phen)₂(sulf-dpp)]Cl₂, [Os(dpp)₂(sulf-dpp)]Cl₂, and [Os(CO)₂Cl₂(sulf-dpp)], where bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, dpp is 4,7-diphenyl-1,10-phenanthroline, and sulf-dpp is bathophenanthrolinedisulfonic acid disodium salt. The family of complexes showed minimal oxygen quenching, making them particularly well-suited for sensing applications in which oxygen concentration varies. Luminescence anisotropy was found to depend more significantly on net dipole moment than hydrodynamic radius of the molecule, and, as expected, excited state lifetime and luminescence anisotropy were highly dependent on the local environment of the reporter molecule. Results obtained for hydrogel-based relative humidity sensors containing [Os(CO)₂Cl₂(sulf-dpp)] and [Os(bpy)₂(sulf-dpp)]Cl₂ complexes highlight the significant potential for this class of compounds in a hydrogel-supported luminescence-based sensing approach.

Easy entry into reduced Ar-BIANH2 compounds: a new class of quinone/hydroquinone-type redox-active couples with an easily tunable potential

Ar-BIANH2 bearing different substituents on the aryl rings have been synthesized in high yield by reduction of the corresponding bis(aryl)acenaphthenequinonediimine (Ar-BIAN) compounds. The structure of p-CH3 C6 H4 -BIANH2 in the solid state was determined by X-ray diffraction. An exhaustive voltammetric investigation of the two parallel BIAN and BIANH2 series afforded a first rationalization of the redox properties of these molecules, highlighting their analogies with quinone/hydroquinone systems. Such analogies, in combination with the much more negative reduction potential range of Ar-BIAN compounds with respect to quinones, can afford to extend the range of reduction potentials so far obtainable by the use of quinones.

Spectral and thermal studies on ruthenium carbonyl complexes with 5-trifluoromethyl-2,4-dihydropyrazol-3-one ligands

Reactions of the cluster compound [Ru(3)(CO)(12)] with 5-trifluoromethyl-2,4-dihydropyrazol-3-one (HL(1)), 4-(2,4-dichlorophenylhydrazono)-5-trifluoromethyl-2,4-dihydropyrazol-3-one (H(2)L(2)), 4-(3-fluorophenylhydrazono)-5-trifluoromethyl-2,4-dihydropyrazol-3-one (H(2)L(3)), 4-(3-trifuoloromethyl-phenylhydrazono)-5-trifluoromethyl-2,4-dihydropyrazol-3-one (H(2)L(4)) and 4-(3-nitrophenylhydrazono)-5-trifluoromethyl-2,4-dihydropyrazol-3-one (H(2)L(5)) have been carried out in benzene and under reduced pressure. The structures of the isolated complexes were elucidated using elemental analyses, IR, UV-vis, mass and NMR spectroscopy. All the complexes are diamagnetic and have trigonal bipyramidal structures with general formulae [Ru(CO)(4)(HL(1))] and [Ru(CO)(3)(H(2)L(2-5))]. The thermal decompositions of the complexes were studied in correlation with the mass spectral fragmentation patterns.

Neutral RuII-Based Emitting Materials: A Prototypical Study on Factors Governing Radiationless Transition in Phosphorescent Metal Complexes

In addition to the metal-centered dd transition that is widely accepted as a dominant radiationless decay channel, other factors may also play important roles in governing the loss of phosphorescence efficiency for heavy-transition-metal complexes. To conduct our investigation, we synthesized two dicarbonylruthenium complexes with formulas [Ru(CO)2(BQ)2] (1) and [Ru(CO)2(DBQ)2] (2), for which the cyclometalated ligands BQ and DBQ denote benzo[h]quinoline and dibenzo[f,h]quinoxaline, respectively. Replacing one CO ligand with a P donor ligand such as PPh2Me and PPhMe2 caused one cyclometalated ligand to undergo a 180 degrees rotation around the central metal atom, giving highly luminous metal complexes [Ru(CO)L(BQ)2] and [Ru(CO)L(DBQ)2], where L = PPh2Me and PPhMe2 (3-6), with emission peaks lambda(max) in the range of 571-656 nm measured in the fluid state at room temperature. It is notable that the S0-T1 energy gap for both 1 and 2 is much higher than that of 3-6, but the corresponding phosphorescent spectral intensity is much weaker. Using these cyclometalated Ru metal complexes as a prototype, our experimental results and theoretical analysis draw attention to the fact that, for complexes 1 and 2, the weaker spin-orbit coupling present within these molecules reduces the T1-S0 interaction, from which the thermally activated radiationless deactivation may take place. This, in combination with the much smaller 3MLCT contribution than that observed in 3-6, rationalizes the lack of room-temperature emission for complexes 1 and 2.

Synthesis, Characterization, and Photophysical Properties of Os(II) Diimine Complexes [Os(N∧N)(CO)2I2] (N∧N = Bipyridine, Phenanthroline, and Pyridyl Benzoxazole)

A new series of Os(II) diimine complexes with the general formula [Os(N(wedge)N)(CO)(2)I(2)], N(wedge)N = 2,2'-bipyridine (bpy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (dbubpy) (2), 4,7-diphenyl-1,10-phenanthroline (dpphen) (3), 2-(2'-pyridyl)benzoxazole (pboz) (4), and 5-tert-butyl-2-(2'-pyridyl)benzoxazole (bupboz) (5), were synthesized and characterized by spectroscopic methods and by a single-crystal X-ray diffraction study on the dpphen complex 3. The corresponding photophysical properties were studied using UV-vis and emission spectrometry. The resulting phosphorescence features both in solution and as a solid film, in combination with the MO calculation, lead us to conclude that the emissions originate from mixed halide-to-ligand (XLCT approximately 70%) and metal-to-ligand (MLCT approximately 30%) transitions instead of the typical MLCT transition. Using complexes 4 and 5 as the dopant emitters, we evaluated their potential to serve as a phosphor for organic light emitting diodes by examining their electroluminescent performances. Reddish orange electroluminescence centered around 600 nm was observed for organic light emitting diodes (OLEDs) fabricated using complex 5 as the emitter; the device efficiency was shown to be as high as 2.8% (and 5.0 cd/A or 2.7 lm/W), and the peak luminance was shown to be 5600 cd/m(2) at a driving voltage of approximately 15 V.

Influence of the Halogen Ligand on the Near-UV−Visible Spectrum of [Ru(X)(Me)(CO)2(α-diimine)] (X = Cl, I; α-Diimine = Me-DAB, iPr-DAB; DAB = 1,4-Diaza-1,3-butadiene): An ab Initio and TD-DFT Analysis

The near-UV-vis electronic spectroscopy of [Ru(X)(Me)(CO)(2)(iPr-DAB)] (X = Cl or I; iPr-DAB = N,N'-di-isopropyl-1,4-diaza-1,3-butadiene) is investigated through CASSCF/CASPT2 and TD-DFT calculations on the model complexes [Ru(X)(Me)(CO)(2)(Me-DAB)] (X = Cl or I). Convergence of the calculated transition energies for the low-lying metal-to-ligand charge-transfer (MLCT), X-to-ligand charge-transfer (XLCT, X halide ligand), or sigma-bond-to-ligand charge-transfer (SBLCT) to experimental values is analyzed for both methods. On the basis of these accurate calculations, it is shown that whereas the lowest singlet state can be assigned to a nearly pure XLCT state in [Ru(I)(Me)(CO)(2)(Me-DAB)], its character is mainly MLCT in [Ru(Cl)(Me)(CO)(2)(Me-DAB)]. These results are in agreement with time-resolved emission/IR and resonance Raman experimental data. The experimental UV-vis bands are well reproduced by the CASSCF/CASPT2 calculations. The TD-DFT transition energies to the long-range charge transfer states are dramatically affected by the nature of the functional, with lowering leading to meaningless values in the case of nonhybrid functionals. Both methods reproduce well the red shift of the absorption bands on going from the chloride to the iodide complex as well as the shift of the strongly absorbing higher MLCT transition from the visible to the UV domain of energy.

Rhenium Chemistry of Diazabutadienes and Derived Iminoacetamides Spanning the Valence Domain II−VI. Synthesis, Characterization, and Metal-Promoted Regiospecific Imine Oxidation

The reaction of diazabutadienes of type R'N=C(R)-C(R)=NR', L (R = H, Me; R' = cycloalkyl, aryl) with Re(V)OCl(3)(AsPh(3))(2) has furnished Re(V)OCl(3)(L), 1, from which Re(III)(OPPh(3))Cl(3)(L), 2, and Re(V)(NAr)Cl(3)(L), 3, have been synthesized. Chemical oxidation of 2(R = H) by aqueous H(2)O(2) and of 3(R = H) by dilute HNO(3) has yielded Re(IV)(OPPh(3))Cl(3)(L'), 5, and Re(VI)(NAr)Cl(3)(L'), 4, respectively, where L' is the monoionized iminoacetamide ligand R'N=C(H)-C(=O)-NR'(-). Finally, the reaction of Re(V)O(OEt)X(2)(PPh(3))(2) with L has furnished bivalent species of type Re(II)X(2)(L)(2), 6(X = Cl, Br). The X-ray structures of 1 (R = Me, R' = Ph), 3 (R = H, R' = Ph, Ar = Ph), and 4 (R = H, R' = cycloheptyl, Ar = C(6)H(4)Cl) are reported revealing meridional geometry for the ReCl(3) fragment and triple bonding in the ReO (in 1) and ReNAr (in 3 and 4 ) fragments. The cis geometry (two Re-X stretches) of ReX(2)(L)(2) is consistent with maximized Re(II)-L back-bonding. Both ReX(2)(L)(2) and Re(NAr)Cl(3)(L') are paramagnetic (S = (1)/(2)) and display sextet EPR spectra in solution. The g and A values of Re(NAr)Cl(3)(L') are, respectively, lower and higher than those of ReX(2)(L)(2). All the complexes are electroactive in acetonitrile solution. The Re(NAr)Cl(3)(L) species display the Re(VI)/Re(V) couple near 1.0 V versus SCE, and coulometric studies have revealed that, in the oxidative transformation of 3 to 4, the reactive intermediate is Re(VI)(NAr)Cl(3)(L)(+) which undergoes nucleophilic addition of water at an imine site followed by induced electron transfer finally affording 4. In the structure of 3 (R = H, R' = Ph, Ar = Ph), the Re-N bond lying trans to the chloride ligand is approximately 0.1 A shorter than that lying trans to NPh. It is thus logical that the imine function incorporating the former bond is more polarized and therefore subject to more facile nucleophilic attack by water. This is consistent with the regiospecificity of the imine oxidation as revealed by structure determination of 4 (R = H, R' = cycloheptyl, Ar = C(6)H(4)Cl).

UV-visible absorption spectra of [Ru(E)(E')(CO)(2)(iPr-DAB)] (E = E' = SnPh(3) or Cl; E = SnPh(3) or Cl, E' = CH(3); iPr-DAB = N,N'-Di-isopropyl-1,4-diaza-1,3-butadiene): combination of CASSCF/CASPT2 and TD-DFT calculations

The UV-visible absorption spectra of [Ru(E)(E')(CO)(2)(iPr-DAB)] (E = E' = SnPh(3) or Cl; E = SnPh(3) or Cl, E' = CH(3); iPr-DAB = N,N'-di-isopropyl-1,4-diaza-1,3-butadiene) are investigated using CASSCF/CASPT2 and TD-DFT calculations on model complexes [Ru(E)(E')(CO)(2)(Me-DAB)] (E = E' = SnH(3) or Cl; E = SnH(3) or Cl, E' = CH(3); Me-DAB = N,N'-dimethyl-1,4-diaza-1,3-butadiene). The calculated transition energies and oscillator strengths allow an unambiguous assignment of the spectra of the nonhalide complexes [Ru(SnPh(3))(2)(CO)(2)(iPr-DAB)] and [Ru(SnPh(3))(Me)(CO)(2)(iPr-DAB)]. The agreement between the CASSCF/CASPT2 and TD-DFT approaches is remarkably good in the case of these nonhalide complexes. The lowest-energy part of the spectrum (visible absorption) originates in electronic transitions that correspond to excitations from the axial E-Ru-E' sigma(2) orbital into the low-lying pi(DAB) orbital (sigma-bond-to-ligand charge transfer, SBLCT, transitions), while the absorption between 25 000 and 35 000 cm(-1) is due to metal-to-ligand charge transfer (MLCT) excitations from the 4d(Ru) orbitals to pi(DAB) (MLCT). Above 35 000 cm(-1), the transitions mostly correspond to MLCT and SBLCT excitations into pi(CO) orbitals. Analysis of the occupied sigma orbitals involved in electronic transitions of the nonhalide complexes shows that the Kohn-Sham orbitals are generally more delocalized than their CASSCF/CASPT2 counterparts. The CASSCF/CASPT2 and TD-DFT approaches lead to different descriptions of electronic transitions of the halide complexes [Ru(Cl)(2)(CO)(2)(Me-DAB)] and [Ru(Cl)(Me)(CO)(2)(Me-DAB)]. CASSCF/CASPT2 reproduces well the observed blue-shift of the lowest absorption band on going from the nonhalide to halide complexes. TD-DFT systematically underestimates the transition energies of these complexes, although it reproduces the general spectral features. The CASSCF/CASPT2 and TD-DFT techniques differ significantly in their assessment of the chloride contribution. Thus, CASSCF/CASPT2 assigns the lowest-energy absorption to predominantly Ru --> DAB MLCT transitions, while TD-DFT predicts a mixed XLCT/MLCT character, with the XLCT component being predominant. (XLCT stands for halide (X)-to-ligand-charge transfer.) Analysis of Kohn-Sham orbitals shows a very important 3p(Cl) admixture into the high-lying occupied orbitals, in contrast to the CASSCF/CASSPT2 molecular orbitals which are nearly pure 4d(Ru) with the usual contribution of the back-donation to pi(CO) orbitals. Further dramatic differences were found between characters of the occupied sigma orbitals, as calculated by CASSCF/CASPT2 and DFT. They differ even in their bonding character with respect to the axial E-Ru and Cl-Ru bonds. These differences are attributed to a drawback of the DFT technique with respect to the dynamical correlation effects which become very important in complexes with a polar Ru-Cl bond. Similar differences in the CASSCF/CASPT2 and TD-DFT descriptions of the lowest allowed transition of [Ru(Cl)(2)(CO)(2)(Me-DAB)] and [Ru(Cl)(Me)(CO)(2)(Me-DAB)] were found by comparing the changes of Mulliken population upon excitation. This comparison also reveals that CASSCF/CASPT2 generally predicts smaller electron density redistribution upon excitation than TD-DFT, despite the more localized character of CASSCF/CASPT2 molecular orbitals.