Bonding and Electronic Properties of Linear Diethynyl Oligothienoacene-Bridged Diruthenium Complexes and Their Oxidized Forms.

A series of five diruthenium diethynyl complexes based on α,ß-fused oligothienoacenes in the core of the bridging ligands [{Ru(dppe)Cp*}2(µ-C≡C-L-C≡C)] [dppe = 1,2-bis(diphenylphosphino)ethane, Cp* = η5-C5Me5; L = thieno[3,2-b]thiophene (4), thieno[2,3-b]thiophene (5), 3,4-dimethylthieno[2,3-b]thiophene (6), dithieno[3,2-b:2',3'-d]thiophene (7), and thieno[3,2-b]thieno[2',3':4,5]thieno[2,3-d]thiophene (8)] have been synthesized and fully characterized electrochemically and spectroscopically. Elongation of the redox noninnocent oligothienoacene bridge core causes a smaller potential difference between the initial two anodic steps, not seen for free dialkyl oligothienoacenes, and increased positive charge delocalization over the conjugated bridge backbone. The highest occupied molecular orbital of the parent complexes resides predominantly on the oligothienoacene core, with strong participation of the ethynyl linkers and slightly smaller contribution from the metallic termini. This bonding character makes the initial one-electron oxidation symmetrical, as revealed by combined voltammetric and spectroscopic (IR, UV-vis-near-IR, and electron paramagnetic resonance) methods as well as density functional theory (DFT) and time-dependent DFT calculations of truncated and selected nontruncated models of the studied series. The remarkable gradual appearance of two C≡C stretching absorptions in the IR spectra of the monocationic diethynyl complexes is ascribed to increasing vibronic coupling of the IR-forbidden νs(C≡C) mode of the oxidized -[C≡C-core-C≡C]+- bridge with a low-lying π-π*(intrabridge)/metal-to-ligand charge-transfer electronic transition in the near-to-mid-IR spectral region.

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.

Molecular engineering of thiophene- and pyrrole-fused core arylamine systems: Tuning redox properties, NIR spectral responsiveness and bacterial imaging applications.

The thiophene- and pyrrole-fused heterocyclic compounds have garnered significant interest for their distinctive electron-rich characteristics and notable optoelectronic properties. However, the construction of high-performance systems within this class is of great challenge. Herein, we develop a series of novel dithieno[3,2-b:2',3'-d] pyrrole (DTP) and tetrathieno[3,2-b:2',3'-d] pyrrole (TTP) bridged arylamine compounds (DTP-C4, DTP-C12, DTP-C4-Fc, TTP-C4-OMe, TTP-C4, and TTP-C12) with varying carbon chain lengths. The pertinent experimental results reveal that this series of compounds undergo completely reversible multistep redox processes. Notably, TTP-bridged compounds TTP-C4 and TTP-C12 exhibit impressive multistep near-infrared (NIR) absorption alterations with notable color changes and electroluminescent behaviors, which are mainly attributed to the charge transfer transitions from terminal arylamine units to central bridges, as supported by theoretical calculations. Additionally, compound DTP-C4 demonstrates the ability to visually identify gram-positive and gram-negative bacteria. Therefore, this work suggests the promising electroresponsive nature of compounds TTP-C4 and TTP-C12, positioning them as excellent materials for various applications. It also provides a facile approach to constructing high-performance multifunctional luminescent materials, particularly those with strong and long-wavelength NIR absorption capabilities.

[1,2-Bis(diphenyl-phosphino)ethane]-chlorido(η-penta-methyl-cyclo-penta-dien-yl)iron(II) dichloro-methane solvate.

In the title compound, [Fe(C(10)H(15))Cl(C(26)H(24)P(2))]·CH(2)Cl(2), the Fe(II) atom is coordinated by two P atoms from a 1,2-bis-(diphenyl-phosphino)ethane ligand [Fe-P = 2.2130 (7) and 2.2231 (7) Å], a chloride anion [Fe-Cl = 2.3329 (7) Å] and a penta-methyl-cyclo-penta-dienyl (Cp*) ligand [Fe-centroid(Cp*) = 1.732 (3) Å] in a typical piano-stool geometry. In the crystal structure, the complex and solvent mol-ecules are paired via weak C-H⋯Cl inter-actions.

Rutheniumethynyl-Triarylamine Organic-Inorganic Mixed-Valence Systems: Regulating Ru-N Electronic Coupling by Different Aryl Bridge Cores.

Four rutheniumethynyl-triarylamine complexes 1-4 with different aryl bridge cores were prepared. The solid structures of complexes 2-4 were fully confirmed by X-ray single-crystal diffraction analysis. Two consecutive one-electron oxidation processes of complexes 1-4 were attributed to the ruthenium and nitrogen centers, as revealed by cyclic voltammetry and square-wave voltammogram. Results also showed decreasing potential difference ΔE of complexes 1, 3, and 4, with the largest value for 2. Upon chemical oxidation of complexes 1-4 by 1.0 eq oxidation reagents FcPF6 or AgSbF6 , the mixed-valence complexes, except for 2+ , show characteristic broad NIR absorptions in the UV-vis-NIR spectroscopic experiments. NIR multiple absorptions were assigned to NAr2 →RuCp*(dppe) intervalence charge transfer (IVCT) and metal-to-ligand charge transfer transitions by TDDFT calculations. Coupling parameter (Hab ) from Hush theory revealed that increasing electronic communication in 1+ , 3+ , and 4+ . Electron density distribution of the HOMO for neutral molecules (1, 3, and 4) and spin density distribution of the corresponding single-oxidized states (1+ , 3+ , and 4+ ) increases progressively on the bridge as the size of the aromatic system increases, proving incremental contributions from bridge cores during oxidation.

Oxidized divinyl oligoacene-bridged diruthenium complexes: bridged localized radical characters and reduced aromaticity in bridge cores.

A series of bimetallic ruthenium vinyl complexes 1-5 bridged by oligoacenes were synthesized and characterized in this study. Comparative cyclic voltammetry results from 1-5 indicated that the first oxidation potential decreased gradually with the extension of conjugate ligands. Upon oxidation to singly oxidized species 1+-5+, rather small ν(CO) changes in the infrared (IR) spectra and the characteristic bands of metal-to-ligand charge transfer absorptions in the near IR (NIR) region predicted via time-dependent DFT calculations suggested that strong bridged ligands participate in redox processes. NIR absorptions were not observed in complexes 4+ and 5+ possibly because of instability in their twisted and noncoplanar geometry. Electron paramagnetic resonance results and spin density distribution demonstrated that the bridged localized degrees of 1+-5+ successively increased with the extension of oligoacene from benzene to tetracene. Further comparative analysis of neutral molecules and monocations to the aromaticity and π-electron density of bridge cores indicated a step-by-step transformation process from an aromatic to quinoidal radical upon oxidation.

Notable differences between oxidized diruthenium complexes bridged by four isomeric diethynyl benzodithiophene ligands.

Four new diruthenium complexes [{(η(5)-C5Me5)Ru(dppe)}2(µ-C[triple bond, length as m-dash]C-L-C[triple bond, length as m-dash]C)] featuring different bridging isomeric diethynyl benzodithiophenes viz. L = benzo[1,2-b;4,5-b']dithiophene (complex ), benzo[2,1-b;4,5-b']dithiophene (complex ), benzo[1,2-b;3,4-b']dithiophene (complex ) and benzo[1,2-b;4,3-b']dithiophene (complex ), were synthesized and characterized by molecular spectroscopic and crystallographic methods. The subtle changes in the molecular structure introduced by the diethynyl benzodithiophene isomers have a notable impact on the stability of the oxidized complexes and their absorption characteristics in the visible-NIR and IR spectral domains. Electronic properties of stable oxidized complexes [](n+) and [](n+) (n = 1, 2) were investigated by cyclic voltammetry, UV-vis-NIR and IR spectroelectrochemistry as well as DFT and TDDFT calculations. The results document the largely bridge-localized character of the oxidation of parents and . Cations [](+) and [](+) are too unstable at ambient temperature to afford their unambiguous characterization. UV-vis-NIR absorption spectral data combined with TDDFT calculations (BLYP35) reveal that the broad electronic absorption of [](+) and [](+) in the NIR region has a mixed intraligand π-π* and MLCT character, with similar contribution from their spin-delocalized trans and cis conformers. A spin-localized (mixed-valence) rotamer was only observed for [](+) at ambient temperature as a minor component on the time scale of IR spectroscopy.

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.

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.

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.

Dithia[3.3]paracyclophane-bridged bimetallic ruthenium acetylide complexes: synthesis, structures and influence of transannular π-π interactions on their electronic properties.

Two dithia[3.3]paracyclophane-bridged bimetallic ruthenium acetylide complexes 2 and 3, in which the upper deck of the cyclophanes were assembled with naphthalenyl and anthracenyl rings, have been designed and synthesized. X-ray crystal structures of 2 and 3 show that there are effective transannular π­π interactions between the two rings in the cyclophane unit. Electrochemistry studies revealed that the successive introduction of naphthalenyl and anthracenyl rings reduced the thermodynamic stability of the corresponding mixed-valence states of 2 and 3. Radical cations and dications of complexes 2 and 3 were generated after the addition of 1.0 or 2.0 equivalents of ferrocenium hexafluorophosphate ([FcH][PF6]). The ν(C≡C) of radicals 2+ and 3+ shift 86 nm and 88 nm in contrast to 2 and 3, respectively. UV-Vis-NIR spectra of 2+ and 3+ exhibited three enveloped transitions in the NIR (10,000­4000 cm(−1)) range. DFT studies showed that the compositions of the FMOs of 2 and 3 are more naphthalenyl and anthracenyl in character than the upper deck of complex 1. Spectroscopy and DFT studies indicated that the influence of transannular π­π interactions on the electronic transitions is more pronounced than in complex 1.