Here, we report multinuclear organometallic molecular wires having the (2,5-diethynylthiophene)diyl-Ru(dppe)2 repeating units. Despite the molecular dimension of 2 – 4 nm the multinuclear wires show high conductance (up to 10–2...

The organometallic AcAHQ/AQ-Ru system turns out to be an effective redox and pH stimuli triggered bimodal molecular switch.

Green and yellow luminescent 4,4′‐dimethyl‐5,5′‐divinyl‐2,2′‐bipyrrole derivatives bearing ester and amide were synthesized from blue luminescent 5,5′‐diformyl‐4,4′‐dimethyl‐2,2′‐bipyrrole and diethyl malonate, 2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione, 1,3‐dimethylbarbituric acid, and 1,3‐dihexylbarbituric acid under Knoevenagel condensation conditions. All the synthesized products clearly showed a red‐shifted π–π* transition absorption band in the visible region compared with the starting bipyrrole. Single‐crystal X‐ray diffraction analysis and 1H nuclear magnetic resonance (NMR) spectroscopy revealed that the carbonyl moiety interacts with NH to form an intramolecular hydrogen‐bonding. Out of the synthesized compounds, a Knoevenagel adduct of 1,3‐dimethylbarbituric acid showed fluorescence at 578 nm with an 88 % quantum efficiency in dichloromethane, which is the highest value for the bipyrrole system. The highly efficient yellow photoluminescence can be attributed to the rigid molecular structure of the compound. Density Functional Theory (DFT) calculation revealed that the rigid and planar structure is essential for the bathochromically shifted absorption and high photoluminescence quantum yield.

Controlling radical localization/delocalization is important for functional materials. The present paper describes synthesis and results of electrochemical, spectroscopic, and theoretical studies of diruthenium (pdiethynylacene)diyl complexes, Me 3 Si-(C�C) 2 -Ru(dppe) 2 -C�CÀ Ar-C�CÀ Ru(dppe) 2 -(C�C) 2 -SiMe 3 (1-6) (dppe: 1,2bis(diphenylphosphino)ethane), and their monocationic radical species ([1] + -[6] + ). The HOMO-LUMO energy gaps can be finely tuned by the acene rings in the bridging ligands installed, as indicated by the absorption maxima of the electronic spectra of 1-6 ranging from the UV region even to the NIR region. The cationic species [1] + -[6] + show two characteristic NIR bands, which are ascribed to the charge resonance (CR) and π-π* transition bands, as revealed by spectroelectrochemistry. Expansion of the acene rings in [1] + -[6] + causes (1) blue shifts of the CR bands and red shifts of the π-π* transition bands and (2) charge localization on the acene parts as evidenced by the ESR, DFT and TD-DFT analyses. Notably, the monocationic complexes of the larger acene derivatives are characterized as the non-classical acene-localized radicals.

The cover picture shows molecular structures of green to yellow luminescent bipyrroles, which consist of two nitrogen-containing aromatic rings. Vinyl groups were introduced to the bipyrroles via Knoevenagel condensation. Their luminescent colors were dependent on the electron withdrawing groups at the terminal of the vinyl groups. Both crystal structure analysis and DFT calculations agreed that cyclic structure at the terminal can reduce thermal deactivation from excited states and promote efficient photoluminescence. Further details of the results can be found in the Full paper by Kawano et al.

Photoluminescent divinylbipyrroles were synthesized from 3,3′,4,4′-tetraetyl-2,2′-bipyrrole-5,5′-dicarboxaldehyde and activated methylene compounds via aldol condensation. For mechanistic clarity, molecular structures of Meldrum’s acid- and 1,3-dimethylbarbituric acid-derived divinylbipyrroles were determined by single-crystal X-ray diffraction. Photoluminescent properties of the synthesized divinylbipyrroles in dichloromethane were found to be dependent on the presence of electron withdrawing groups at the vinylic terminal. The divinylbipyrroles derived from malononitrile, Meldrum’s acid, and 1,3-dimethylbarbituric acid showed fluorescent peaks at 553, 576, and 602 nm respectively. Computational studies indicated that the alkyl substituents on the bipyrrole 3 and 3′ positions increased energy level of the highest occupied molecular orbital (HOMO) compared to the unsubstituted derivatives and provided rationale for the bathochromic shift of the ultraviolet-visible (UV-Vis) spectra compared to the previously reported analogs.