C7 and C9 Carbon-Rich Bridges in Diruthenium Systems: Synthesis, Spectroscopic, and Theoretical Investigations of Different Oxidation States

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.

Near-infrared dyes for two-photon absorption in the short-wavelength infrared: strategies towards optical power limiting

The recent advances in the field of two-photon absorbing chromophores in the short-wavelength infrared spectral range (SWIR 1100–2500 nm) are summarized, highlighting the development of optical power limiting devices in this spectral range.

Understanding the singlet–triplet energy splittings in transition metal-capped carbon chains

Density functional theory and molecular orbital analysis suggest that the odd–even alternation of singlet–triplet energy separations is a general feature of transition metal-capped carbon chains, determined primarily by the carbon chains.

Most favorable cumulenic structures in iron-capped linear carbon chains are short singlet odd-carbon dications: a theoretical view

DFT computations suggest that the odd iron-capped linear-carbon dications exhibit large ΔE_S–T values and more cumulenic structures than short even-carbon chains.

Asymmetric oxidation of vinyl- and ethynyl terthiophene ligands in triruthenium complexes

Newly synthesized open-triangle triruthenium vinyl and ethynyl terthiophene complexes exhibit stepwise laterally localized oxidation processes, as revealed by UV-vis-NIR and IR spectroelectrochemistry.

Rapid Markovnikov addition of HCl to a pendant alkyne: evidence for a quinoidal cumulene

The reaction of the vinylidene cations trans-[Ru(CCH–C₆H₂-2,5-R₂-4-CCH)Cl(dppm)₂]⁺ (R = H, Me) with chloride results in Markovnikov addition of HCl to the terminal alkyne, suggesting the intermediacy of a quinoidal cumulene complex.

Organosilver(I) framework assembly with trifluoroacetate and enediyne-functionalized alicycles

Eight new silver(I) trifluoroacetate complexes based on a series of designed ligands, each featuring an alicyclic ring with enediyne functionality, have been synthesized and characterized by single-crystal X-ray diffraction. Each ethynide terminal is inserted into an Agn (n = 4-5) basket, leading to the generation of coordination chain or layer structures, but the well shielded ethenyl group does not take part in silver-olefin bonding. Variation in ring size of the alicycles is shown to influence the construction of the organosilver(I) coordination networks, which are consolidated by weak intermolecular interactions in the crystal structures. The effect of adding ancillary N-donor ligands to the reaction system on the coordination and supramolecular network assembly is also investigated.

Metal complexes containing allenylidene and higher cumulenylidene ligands: a theoretical perspective

Transition metal complexes containing unsaturated carbenes have enjoyed a recent surge in research interest. In addition to showing potential as molecular wires and as components of opto-electronic materials, they provide multifaceted reactive sites for organic synthesis. In this Account, we describe results of recent theoretical studies that delineate the main features of electronic structure and bonding in allenylidenes and higher cumulenylidene complexes, [L(m)M]═C(═C)(n)═CR(1)R(2) (where L represents the ligand, M the metal, and n ≥ 1). Although free cumulenylidene ligands, :C(═C)(n)═CR(1)R(2), are extremely unstable and reactive species, they can be stabilized by coordination to a transition metal. The σ-donation of the electron lone pair on the terminal carbon atom to an empty metal d-orbital, together with the simultaneous π back-donation from filled metal d(π)-orbitals to empty cumulene π* system orbitals, leads to the formation of a strong M═C bond with multiple character. Density functional theory studies on the model systems [(CO)(5)Cr(═C)(n)CH(2)] and [trans-Cl(PH(3))(4)Ru(═C)(n)CH(2)](+) (where n = 1-9) have been useful in interpreting the structural and spectroscopic properties and the reactivity of this class of complexes. Geometry optimizations significantly contributed to the generalization of the sparse structural data available for allenylidene, butatrienylidene, and pentatetraenylidene complexes to higher cumulenylidene complexes (with up to eight carbon atoms in the chain), which show a clear structural trend. In particular, the geometries of all even-chain cumulenes are consistent with an almost purely cumulenic structure, whereas the geometries of odd-chain cumulenes present a significant polyyne-like carbon-carbon bond length alternation. The calculated bond dissociation energies (BDEs) of the cumulenylidene ligand remain almost constant on lengthening the cumulene chain. These BDEs indicate that there is no thermodynamic upper limit to the cumulene chain length and suggest that the synthetic difficulties in preparing higher cumulenylidenes are due to an increase in reactivity. The calculated charges on the carbon atoms show no significant polarization along the cumulene chain, indicating that charge distribution is not important in determining the regioselectivity of either electrophilic or nucleophilic attack, which is instead determined by frontier orbital factors. The breakdown of the contributions from the metal and the carbon atoms along the chain to the HOMO and LUMO shows that the HOMO has contributions mainly from the metal and the carbon atoms in even positions along the chain (C(2), C(4), C(6), and higher). In contrast, the LUMO has contributions mainly from the carbon atoms in odd positions along the chain (C(1), C(3), C(5), and higher), thus explaining the experimentally observed regioselectivity of electrophilic and nucleophilic attacks, which are directed, respectively, to even and odd positions of the cumulenylidene chain. The study of the electronic structure of cumulenylidenes has allowed us not only to give a consistent rationale for the main structural and spectroscopic properties and for the reactivity of this emerging class of compounds but also to predict the effect of ancillary ligands on the metal center or substituents on the carbon end. The result is a useful guide to new developments in the still-underexplored fields of this fascinating class of compounds.

Electronic communication in dinuclear C(4)-bridged tungsten complexes

The dinuclear tungsten carbyne [X(CO)(2)(dppe)WC(4)W(dppe)(CO)(2)X] (dppe = 1,2-bis(diphenylphosphino)ethane; X = I (3), Cl (7)) complexes were prepared from the bisacetylide precursor Li(2)[(CO)(3)(dppe)WC(4)W(CO)(3)(dppe)] (2) via oxidative replacement of one CO group at each tungsten center with a halide substituent. The iodide ligand in 3 could be substituted with isothiocyanate or triflate resulting in [X(CO)(2)(dppe)WC(4)W(dppe)(CO)(2)X] complexes (X = NCS (8), OTf (9)). Substitution of two and all four CO ligands in 3 was achieved via subsequent photolytic or thermal activation with dppe. The "half-substituted" complex [I(CO)(2)(dppe)WC(4)W(dppe)(2)I] (11) allows reversible one-electron oxidation which results in the monocationic species [I(CO)(2)(dppe)WC(4)W(dppe)(2)I][PF(6)] (11[PF(6)]). The "all-dppe substituted" complex [I(dppe)(2)WC(4)W(dppe)(2)I] (10) possesses two reversible redox states leading to the stable monocationic [I(dppe)(2)WC(4)W(dppe)(2)I][PF(6)] (10[PF(6)]) and the dicationic [I(dppe)(2)WC(4)W(dppe)(2)I][PF(6)](2) (10[PF(6)](2)) compounds. The complexes 2, 3, [W(CO)(3)(dppe)(C[triple bond]CPh)(I)] (4), [X(CO)(2)(dppe)W[triple bond]C-C(Me)=C(Me)-C[triple bond]W(dppe)(CO)(2)X] (X = I (5), Cl (6)), 7, 8, 10, 11 and 11[PF(6)] were characterized by single crystal X-ray diffraction. The electronic properties of complexes 10, 10[PF(6)], 10[PF(6)](2), as well as of compounds 11 and 11[PF(6)], were investigated using cyclic voltammetry (CV), EPR, IR, near-IR spectroscopy, and magnetization measurements. These studies showed that the [W][triple bond]C-C[triple bond]C-C[triple bond][W] canonical form of the bridged system with strong tungsten-carbon interaction contributes significantly to the electronic coupling in the mixed-valent species 10[PF(6)] (comproportionation constant K(c) = 7.5 x 10(4)) and to the strong antiferromagnetic coupling in the dicationic complex 10[PF(6)](2) (exchange integral J = -167 cm(-1)). In addition, the rate for electron transfer between the tungsten centers in 10[PF(6)] was evaluated by near-IR and IR studies.