Charge Delocalization in an Organic Mixed Valent Bithiophene Is Greater Than in a Structurally Analogous Biselenophene

Intramolecular Through-Space Double-Electron Transfer Between A Pair of Redox-Active Guanidine Units Aligned by Dithiolate Bridges

Using unconventional synthesis protocols, two redox-active triguanidine units are connected by a dithiolate bridge, aligning the two redox-active units in close proximity. The reduced, neutral and the tetracationic redox states with two dicationic triguanidine units are isolated and fully characterized. Then, the dicationic redox states are prepared by mixing the neutral and tetracationic molecules. At low temperatures, the dications are diamagnetic (singlet ground state) with two different triguanidine units (neutral and dicationic). At room temperature, the triplet state with two radical monocationic triguanidine units is populated. At low temperature (210 K), chemical exchange by intramolecular through-space electron-transfer between the two triguanidine units is evidenced by EXSY NMR spectroscopy. Intramolecular through-space transfer of two electrons from the neutral to the dicationic triguanidine unit is accompanied by migration of the counterions in opposite direction. The rate of double-electron transfer critically depends on the bridge. No electron-transfer is measured in the absence of a bridge (in a mixture of one dicationic and one neutral triguanidine), and relatively slow electron transfer if the bridge does not allow the two triguanidine units to approach each other close enough. The results give detailed, quantitative insight into the factors that influence intramolecular through-space double-electron-transfer processes.

Electron-Rich Diruthenium Complexes with π-Extended Alkenyl Ligands and Their F4 TCNQ Charge-Transfer Salts

The synthesis of dinuclear ruthenium alkenyl complexes with {Ru(CO)(Pⁱ Pr₃ )₂ (L)} entities (L=Cl^- in complexes Ru₂ -3 and Ru₂ -7; L=acetylacetonate (acac^- ) in complexes Ru₂ -4 and Ru₂ -8) and with π-conjugated 2,7-divinylphenanthrenediyl (Ru₂ -3, Ru₂ -4) or 5,8-divinylquinoxalinediyl (Ru₂ -7, Ru₂ -8) as bridging ligands are reported. The bridging ligands are laterally π-extended by anellating a pyrene (Ru₂ -7, Ru₂ -8) or a 6,7-benzoquinoxaline (Ru₂ -3, Ru₂ -4) π-perimeter. This was done with the hope that the open π-faces of the electron-rich complexes will foster association with planar electron acceptors via π-stacking. The dinuclear complexes were subjected to cyclic and square-wave voltammetry and were characterized in all accessible redox states by IR, UV/Vis/NIR and, where applicable, by EPR spectroscopy. These studies signified the one-electron oxidized forms of divinylphenylene-bridged complexes Ru₂ -7, Ru₂ -8 as intrinsically delocalized mixed-valent species, and those of complexes Ru₂ -3 and Ru₂ -4 with the longer divinylphenanthrenediyl linker as partially localized on the IR, yet delocalized on the EPR timescale. The more electron-rich acac^- congeners formed non-conductive 1 : 1 charge-transfer (CT) salts on treatment with the F₄ TCNQ electron acceptor. All spectroscopic techniques confirmed the presence of pairs of complex radical cations and F₄ TCNQ^.- radical anions in these CT salts, but produced no firm evidence for the relevance of π-stacking to their formation and properties.

End-to-end communication in a linear supermolecule with a BOPHY centre and N,N-dimethylanilino-based terminals

Long-range electrostatic interactions are sufficient to cause sequential ionization of the terminal groups in a BOPHY-based supermolecule.

Tuning the Electronic Coupling and Electron Transfer in Mo2 Donor-Acceptor Systems by Variation of the Bridge Conformation

Assembling two quadruply bonded dimolybdenum units [Mo2 (DAniF)3 ](+) (DAniF=N,N'-di(p-anisyl)formamidinate) with 1,4-naphthalenedicarboxylate and its thiolated derivatives produced three complexes [{Mo2 (DAniF)3 }2 (μ-1,4-O2 CC10 H6 CO2 )], [{Mo2 (DAniF)3 }2 (μ-1,4-OSCC10 H6 COS)], and [{Mo2 (DAniF)3 }2 (μ-1,4-S2 CC10 H6 CS2 )]. In the X-ray structures, the naphthalene bridge deviates from the plane defined by the two Mo-Mo bond vectors with the torsion angle increasing as the chelating atoms of the bridging ligand vary from O to S. The mixed-valent species exhibit intervalence transition absorption bands with high energy and very low intensity. In comparison with the data for the phenylene analogues, the optically determined electronic coupling matrix elements (Hab =258-345 cm(-1) ) are lowered by a factor of two or more, and the electron-transfer rate constants (ket ≈10(11)  s(-1) ) are reduced by about one order of magnitude. These results show that, when the electron-transporting ability of the bridge and electron-donating (electron-accepting) ability of the donor (acceptor) are both variable, the former plays a dominant role in controlling the intramolecular electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO-LUMO energy gap by elevating the (bridging) ligand-based LUMO energy. Therefore, our experimental results and theoretical analyses verify the superexchange mechanism for electronic coupling and electron transfer.

Convenient synthesis of organic-electronics-oriented building blocks via on-water and under-air homocoupling of (hetero)aryl iodides

An on-water homocoupling reaction is developed for the alternative synthesis of various organic-electronically versatile bi(hetero)aryls. These multi-function building blocks are indispensable to polymer chemistry and modern organic electronics.