Ya-Ping Ou

Experimental and Theoretical Studies of Charge Delocalization in Biruthenium–Alkynyl Complexes Bridged by Thiophenes

A series of binuclear ruthenium-alkynyl complexes that are bridged by thiophene groups (thiophene, bithiophene, and terthiophene) have been synthesized. All of these complexes have been well-characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. The electronic properties of these complexes have been examined by using cyclic voltammetry, UV/Vis/NIR and IR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT) calculations. Electrochemical results showed that the potential difference (ΔE) and comproportionation constant (Kc) decreased with increasing size of the thiophene bridging unit. The UV/Vis/NIR spectra and TDDFT calculations of the monocations indicated that the NIR transitions displayed aromatic bridging character. EPR studies of the mono-oxidized radical species further demonstrated that the unpaired electron/hole was delocalized over both metals and the bridging ligand and established significant participation in the ligand oxidation.

Bridge-localized HOMO-binding character of divinylanthracene-bridged dinuclear ruthenium carbonyl complexes: spectroscopic, spectroelectrochemical, and computational studies.

The electronic properties of four divinylanthracene-bridged diruthenium carbonyl complexes [{RuCl(CO)(PMe3)3}2(μ-CH=CHArCH=CH)] (Ar=9,10-anthracene (1), 1,5-anthracene (2), 2,6-anthracene (3), 1,8-anthracene (4)) obtained by molecular spectroscopic methods (IR, UV/Vis/near-IR, and EPR spectroscopy) and DFT calculations are reported. IR spectroelectrochemical studies have revealed that these complexes are first oxidized at the noninnocent bridging ligand, which is in line with the very small ν(C≡O) wavenumber shift that accompanies this process and also supported by DFT calculations. Because of poor conjugation in complex 1, except oxidized 1(+), the electronic absorption spectra of complexes 2(+), 3(+), and 4(+) all display the characteristic near-IR band envelopes that have been deconvoluted into three Gaussian sub-bands. Two of the sub-bands belong mainly to metal-to-ligand charge-transfer (MLCT) transitions according to results from time-dependent DFT calculations. EPR spectroscopy of chemically generated 1(+)-4(+) proves largely ligand-centered spin density, again in accordance with IR spectra and DFT calculations results.

Conformational Tuning of the Intramolecular Electronic Coupling in Molecular-Wire Biruthenium Complexes Bridged by Biphenyl Derivatives

The synthesis and characterization of a series of biphenyl-derived binuclear ruthenium complexes with terminal {RuCl(CO)(PMe3)3} moieties and different structural arrangements of the phenyl rings are reported. Electrochemical studies revealed that the two metal centers of the binuclear ruthenium complexes interact with each other through the biphenyl bridge, and the redox splittings ΔE1/2 show a strong linear correlation with cos(2)  ϕ, where ϕ is the torsion angle between the two phenyl rings. A combination of electrochemical, UV/Vis/NIR, and in situ IR differential spectroelectrochemical analysis clearly showed that: 1) the intramolecular electronic couplings in the binuclear ruthenium complexes could be modulated by changing ϕ; 2) the electronic ground state of the mixed-valent cations changes from delocalized to localized through the biphenyl bridge with increasing torsion angle ϕ, that is, the redox processes of these complexes change from significant involvement of the bridging ligand to an oxidation behavior with less participation of the bridge.

Bimetallic ruthenium complexes bridged by divinylphenylene bearing oligo(ethylene glycol)methylether: synthesis, (spectro)electrochemistry and the lithium cation effect

A series of 1,4-disubstituted ruthenium-vinyl complexes, (E,E)-[{(PMe3)3(CO)ClRu}2(μ-HC=CH-Ar-CH=CH)], in which the 1,4-diethenylphenylene bridge bears two oligo(ethylene glycol)methyl ether side chains at different positions (2,5- and 2,3-positions), were prepared. The respective products were characterized by elemental analyses and NMR spectroscopy. The structures of complexes 1b and 1e were established by X-ray crystallography. The electronic properties of the complexes were investigated by cyclic voltammetry, and IR and UV-vis/NIR spectroscopies. Electrochemical studies showed that the 2,5-substituents better stabilized the mixed-valence states; the electrochemical behavior was greatly affected by lithium cations, especially complex 1g with 2,3-substituents, which was further supported by IR and UV-vis/NIR spectra changes. Spectroelectrochemical studies showed that the redox chemistry was dominated by the non-innocent character of the bridging fragment.

2Rotaxane based on terpyridyl bimetal ruthenium complexes and β-cyclodextrin as organic sensitizer for dye-sensitized solar cells

The conjugated carboxy-functionalized terpyridyl bimetal ruthenium complex [(tdctpy)Ru(dctpy-(ph)4-dctpy)Ru(tdctpy)][PF6]4 and [2]rotaxane by self-assembly of [(tdctpy)Ru(dctpy-(ph)4-dctpy)Ru(tdctpy)][PF6]4 with β-cyclodextrin are reported as sensitizer for dye-sensitized solar cells (DSSCs), where tdctpy = 4′-p-tolyl-4,4″-dicarboxy-2,2′ : 6,2″-terpyridine, dctpy = 4,4″-dicarboxy-2,2′ : 6,2″-terpyridine and dctpy-(ph)4-dctpy represents a bridging ligand where two 4,4″-dicarboxy-2,2′ : 6′,2″-terpyridine units are connected through four phenyl spacers in the 4′-position. The DSSCs fabricated utilizing these materials give typical electric power conversion efficiency of 0.013–0.523% under air mass (AM) 1.5, 100 mW cm−2 irradiation at room temperature. The terpyridyl bimetal ruthenium complex [(tdctpy)Ru(dctpy-(ph)4-dctpy)Ru(tdctpy)][PF6]4 with conjugated-bridge chains displayed much higher conversion efficiency compared with the carboxy-functionalized terpyridyl monometal ruthenium complex [tdctpy-Ru-(idctpy)][PF6]2, where idctpy = 4′-p-iodophenyl-4,4″-dicarboxy-2,2′ : 6,2″-terpyridine. [2]Rotaxane displayed the highest electric power conversion efficiency of 0.523% when β-cyclodextrin was introduced into the conjugated terpyridyl bimetal ruthenium complex and formed [2]rotaxane.

Substituted diethynyldithia[3.3]paracyclophanes—synthetically more accessible new building blocks for molecular scaffolding

A series of dialkyne building blocks based on the dithia[3.3]paracyclophane unit have been synthesized in good yields. The electronic properties of these novel dialkynes can be tuned through a transannular substitution effect. These synthetically more accessible diethynyldithia[3.3]paracyclophanes are promising candidates for the building of relatively carbon rich molecular scaffolds.

Mononuclear piano-stool iron 2-ethynylbenzo[b]thiophene complex: crystal structure and reversible oxidation studied by spectro-electrochemical and DFT methods

Abstract A mononuclear iron complex with 2-ethynylbenzo[b]thiophene C-coordinated to the (η5-Cp*)(η2-dppe)Fe (Cp* = pentamethylcyclopentadienyl, dppe = 1,2-diphenylphosphinoethane) framework (1) was prepared and characterized by 1H NMR, elemental analysis, and single crystal X-ray diffraction. The redox behavior of 1 was investigated by voltammetric methods and anodic spectroelectrochemistry in the UV–vis-NIR-IR region and compared with reference complexes including 2-ferrocenylbenzo[b]thiophene (2) and the 2-ethynylpyridine derivative of 1. The spin density distribution along the linear molecular backbone in 1+ was analyzed by DFT (BLYP35) and TDDFT calculations of a truncated model complex. The combined experimental and theoretical results revealed an important role of the ethynylene linker in determining the redox properties of this family of complexes and participation of the 2-ethynylbenzo[b]thiophene framework in the largely iron-based anodic electron transfer.