High Molecular Conductance and Inverted Conductance Decay over 3 nm in Aminium-Terminated Carbon-Bridged Oligophenylene-Vinylenes.

With the progressing miniaturization of electronic device components to improve circuit density while retaining or even reducing spatial requirements, single molecules employed as electric components define the lower limit of accessible structural width. To circumvent the typical exponential conductance decay for increasing length in molecule-based wires, topological states, which describe the occurrence of discontinuities of a bulk material's electronic structure confined to its surface, can be realized for molecules by the introduction of unpaired spins at the molecular termini. The resulting high conductance and reversed conductance decay are typically only observed for shorter molecules, as the terminal spins must be within the electronic coupling range to produce the desired effects.

A Molecular Engineering Approach to Conformationally Regulated Conductance Dualism in a Molecular Junction.

One key aspect for the development of functional molecular electronic devices is the ability to precisely tune and reversibly switch the conductance of individual molecules in electrode-molecule-electrode junctions in response to external stimuli. In this work, we present a new approach to access molecular switches by deliberately controlling the flexibility in the molecular backbone. We here describe two new conductance switches based on bis(triarylamines) that rely on the reversible toggling between two conformers, each associated with vastly different conductances.

The Emissive and Electrochemical Properties of Hypervalent Pyridine-Dipyrrolide Bismuth Complexes.

We present a series of six hypervalent bismuth complexes Bi(PDP)X bearing ligands characterized by the pyridine-2,6-bis(pyrrolide) (PDP) structural motif. While bismuth holds considerable potential for facilitating efficient intersystem crossing (ISC), reports on phosphorescent molecular bismuth complexes are still scarce and mostly based on systems that exhibit inter- or intraligand charge transfer character of their optical excitations. Herein, the UV/vis absorptive, luminescent, and electrochemical properties of complexes Bi(PDP)X are explored, where the substituents R and R, as well as the halide ligand X are varied.

Dimerization of 9-Phenyl-ferroceno[2,3]indenylmethyl Radicals: Electrochemical and Spectroelectrochemical Studies.

We report on three new 9-phenyl-substituted ferroceno[2,3]indenylmethylium dyes - with electron-donating (OMe, Me) or electron-withdrawing (CF) substituents. Complexes - exist as racemic mixtures of and enantiomers. Pyramidalization at the methyl C atom in the precursor carbinol species - or the corresponding one-electron reduced radicals induces a second stereocenter, as the 9-phenyl substituent may reside in an or an position.

Dual Fluorescence and Phosphorescence Emissions from Dye-Modified ()-Bismuth Pincer Thiolate Complexes.

We report the synthesis, characterization, and photophysical properties of four new dye-modified ()Bi pincer complexes with two mercaptocoumarin or mercaptopyrene ligands. Their photophysical properties were probed by UV/vis spectroscopy, photoluminescence (PL) studies, and time-dependent density functional theory (TD-DFT) calculations. Absorption spectra of the complexes are dominated by mixed pyrene or coumarin π → π*/n(pS) → pyrene or coumarin π* transitions.

Fully Reprogrammable 2D Array of Multistate Molecular Switching Units.

Integration of molecular switching units into complex electronic circuits is considered to be the next step toward the realization of novel logic and memory devices. This paper reports on an ordered 2D network of neighboring ternary switching units represented by triazatruxene (TAT) molecules organized in a honeycomb lattice on a Ag(111) surface. Using low-temperature scanning tunneling microscopy, the bonding configurations of individual TAT molecules can be controlled, realizing up to 12 distinct states per molecule.

Pyrene fluorescence in 2,7-di(4-phenylethynyl)pyrene-bridged bis(alkenylruthenium) complexes.

Complexes PyrDPE-RuCl and PyrDPE-Ruacac with a π-extended 2,7-di(4-phenylethynyl)pyrene linker undergo simultaneous one-electron oxidations of their {Ru}-styryl entities. The absence of an intervalence charge-transfer (IVCT) band at intermediate stages, where the mixed-valent, singly oxidized radical cation is present, and spin density confinement to the terminal styryl ruthenium site(s) are tokens of a lack of electronic coupling between the {Ru} entities across the π-conjugated linker. The close similarity of the linker-based π → π* bands in the complexes and the free ligand and their insensitivity towards oxidations at the terminal sites indicate that the central pyrenyl fluorophore is electronically decoupled from the electron-rich {Ru}-styryl termini.

A Dibenzotetrathiafulvalene-Bridged Bis(alkenylruthenium) Complex and Its One- and Two-Electron-Oxidized Forms.

We report on the synthesis of the new bis(alkenylruthenium) complex with a longitudinally extended, π-conjugated dibenzotetrathiafulvalene (DBTTF) bridge, characterized by multinuclear NMR, IR, and UV/vis spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Cyclic and square-wave voltammetry revealed that undergoes four consecutive oxidations. IR, UV/vis/near-IR, and electron paramagnetic resonance spectroscopy indicate that the first oxidation involves the redox-noninnocent DBTTF bridge, while the second oxidation is biased toward one of the peripheral styrylruthenium entities, thereby generating an electronically coupled mixed-valent state ({Ru}-CH═CH)-DBTTF-(CH═CH-{Ru}) [{Ru} = Ru(CO)Cl(PPr)].

Ferrocenyl-Substituted Triazatruxenes: Synthesis, Electronic Properties, and the Impact of Ferrocenyl Residues on Directional On-Surface Switching on Ag(111).

We report on seven new ferrocenyl-(, )- and ferrocenylethynyl-modified ,',″-triethyltriazatruxenes (s) - as well as the dodecyl counterpart of compound and their use as molecular switching units when deposited on a Ag(111) surface. Such functional units may constitute a new approach to molecule-based high-density information storage and processing. Besides the five compounds -, , and , where the 3-fold rotational symmetry of the triazatruxene (TAT) template is preserved, we also included 2-ethynylferrocenyl-TAT and 2,2'-di(ethynylferrocenyl)-TAT , whose mono- and disubstitution patterns break the 3-fold symmetry of the TAT core.

Linker permethylation as a means to foster valence tautomerism and thwart dimerization in ferrocenyl-triarylmethylium cations.

Permethylation of the phenylene linker in a cationic ferrocenyl-phenylthioxanthylium dyad increases the amount of the diradical ferrocenium thioxanthyl radical valence tautomer and aids in supressing dimerization of the latter and of the one-electron reduced neutral radical.

Single-molecule conductance studies on quasi- and metallaaromatic dibenzoylmethane coordination compounds and their aromatic analogs.

The ability to predict the conductive behaviour of molecules, connected to macroscopic electrodes, represents a crucial prerequisite for the design of nanoscale electronic devices. In this work, we investigate whether the notion of a negative relation between conductance and aromaticity (the so-called NRCA rule) also pertains to quasi-aromatic and metallaaromatic chelates derived from dibenzoylmethane (DBM) and Lewis acids (LAs) that either do or do not contribute two extra electrons to the central resonance-stabilised β-ketoenolate binding pocket. We therefore synthesised a family of methylthio-functionalised DBM coordination compounds and subjected them, along with their truly aromatic terphenyl and 4,6-diphenylpyrimidine congeners, to scanning tunneling microscope break-junction (STM-BJ) experiments on gold nanoelectrodes.

Organic binary charge-transfer compounds of 2,2' : 6',2'' : 6'',6-trioxotriphenylamine and a pyrene-annulated azaacene as donors.

Three binary charge-transfer (CT) compounds resulting from the donor 2,2' : 6',2'' : 6'',6-trioxotriphenylamine (TOTA) and the acceptors FTCNQ and FBQ and of a pyrene-annulated azaacene (PAA) with the acceptor FTCNQ are reported. The identity of these CT compounds are confirmed by single-crystal X-ray diffraction as well as by IR, UV-vis-NIR and EPR spectroscopy. X-ray diffraction analysis reveals a 1 : 1 stoichiometry for TOTA·FTCNQ, a 2 : 1 donor : acceptor ratio in (TOTA)·FBQ, and a rare 4 : 1 stoichiometry in (PAA)·FTCNQ, respectively.

Reversible Multielectron Release from Redox-Active Three-Dimensional Molecular Barrels with Ruthenium-Alkenyl Moieties.

Three-dimensional molecular barrels and were synthesized in high yields from dinuclear ruthenium-vinyl clamps and tritopic triphenylamine-derived carboxylate linkers and characterized by multinuclear NMR spectroscopy including H-H COSY and H DOSY measurements, high-resolution electrospray ionization mass spectrometry, and X-ray crystallography. The metal frameworks of the cages adopt the shape of twisted trigonal prisms, and they crystallize as racemic mixtures of interdigitating Δ- and Λ-enantiomers with a tight columnar packing in . Electrochemical studies and redox titrations revealed that the cages are able to release up to 11 electrons on the voltammetric timescale and that their cage structures persist up to the hexacation level.

Exploring Structure-Property Relations of B,S-Doped Polycyclic Aromatic Hydrocarbons through the Trinity of Synthesis, Spectroscopy, and Theory.

Polycyclic aromatic hydrocarbons (PAHs) are prominent lead structures for organic optoelectronic materials. This work describes the synthesis of three B,S-doped PAHs with heptacene-type scaffolds via nucleophilic aromatic substitution reactions between fluorinated arylborane precursors and 1,2-(MeSiS)CH/1,8-diazabicyclo[5.4.

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

The synthesis of dinuclear ruthenium alkenyl complexes with {Ru(CO)(P Pr ) (L)} entities (L=Cl in complexes Ru -3 and Ru -7; L=acetylacetonate (acac ) in complexes Ru -4 and Ru -8) and with π-conjugated 2,7-divinylphenanthrenediyl (Ru -3, Ru -4) or 5,8-divinylquinoxalinediyl (Ru -7, Ru -8) as bridging ligands are reported. The bridging ligands are laterally π-extended by anellating a pyrene (Ru -7, Ru -8) or a 6,7-benzoquinoxaline (Ru -3, Ru -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.

Five shades of green: substituent influence on the (spectro-) electrochemical properties of diferrocenyl(phenyl)methylium dyes.

Five new, intensely green diferrocenylphenylmethylium complexes 1+-5+ with electron donating (EDG: 4-MeO, 4-Me, 4-Br) or withdrawing (EWG: 3,5-CF, 4-CF) substituents were synthesized and fully characterized. The substituent influence on their electrochemical and spectroscopic properties was investigated by cyclic voltammetry, UV/Vis/NIR and -dependent EPR spectroscopy of the cationic as well as the oxidized (12+-52+) and reduced (1˙-5˙) species. The reduced forms equilibrate with their corresponding dimers (65-83%) with a clear substituent influence as expressed by their Hammett parameters in an ordering 4+ > 5+ > 3+ > 2+ > 1+.

A "Pretender" Croconate-Bridged Macrocyclic Tetraruthenium Complex: Sizable Redox Potential Splittings despite Electronically Insulated Divinylphenylene Diruthenium Entities.

Careful optimization of the reaction conditions provided access to the particularly small tetraruthenium macrocycle , which is composed out of two redox-active divinylphenylene-bridged diruthenium entities {Ru}-1,4-CH=CH-CH-CH=CH-{Ru} (RuPh; {Ru} = Ru(CO)Cl(PPr)) and two likewise redox-active and potentially non-innocent croconate linkers. According to single X-ray diffraction analysis, the central cavity of is shielded by the bulky PPr ligands, which come into close contact. Cyclic voltammetry revealed two pairs of split anodic waves in the weakly ion pairing CHCl/NBuBAr (BAr = [B{CH(CF)-3,5}] electrolyte, while the third and fourth waves fall together in CHCl/NBuPF.

Ferro-self-assembly: magnetic and electrochemical adaptation of a multiresponsive zwitterionic metalloamphiphile showing a shape-hysteresis effect.

Metallosurfactants are molecular compounds which combine the unique features of amphiphiles, like their capability of self-organization, with the peculiar properties of metal complexes like magnetism and a rich redox chemistry. Considering the high relevance of surfactants in industry and science, amphiphiles that change their properties on applying an external trigger are highly desirable. A special feature of the surfactant reported here, 1-()-heptenyl-1'-dimethylammonium-methyl-(3-sulfopropyl)ferrocene (), is that the redox-active ferrocene constituent is in a gemini-position.

Tailoring Valence Tautomerism by Using Redox Potentials: Studies on Ferrocene-Based Triarylmethylium Dyes with Electron-Poor Fluorenylium and Thioxanthylium Acceptors.

Three new electrochromic ferrocenyl triarylmethylium dyes with fluorenylium (1 a , 1 b ) or thioxanthylium (1 c ) residues were selected in order to keep the intrinsic differences of redox potentials for ferrocene oxidation and triarylmethylium reduction small and to trigger valence tautomerism (VT). UV/Vis/NIR and quantitative EPR spectroscopy identified paramagnetic diradical isomers 1 a -1 c alongside diamagnetic forms 1 a -1 c , which renders these complexes magnetochemical switches. The diradical forms 1 a -1 c as well as the one-electron-reduced triarylmethyl forms of the complexes were found to dimerize in solution.

Voltammetry as a Tool to Monitor the Aggregation Behavior of a Zwitterionic Ferrocene Surfactant.

Amphiphiles are unique in their ability to self-assemble in aqueous solution into aggregates. The control of the self-organization of amphiphiles and the live monitoring of the ensuing structure changes by analytical methods are key challenges in this field. One way to gain control and to trigger the self-assembly/disassembly of amphiphiles is to introduce a redox-active constituent to the amphiphile structure, as is the case with metallosurfactants.

Redox-Induced Hydrogen Bond Reorientation Mimicking Electronic Coupling in Mixed-Valent Diruthenium and Macrocyclic Tetraruthenium Complexes.

We present the coordination-driven self-assembly of three tetranuclear metallacycles containing intracyclic NH, OH, or OMe functionalities through the combination of various isophthalic acid building blocks with a divinylphenylene diruthenium complex. All new complexes of this study were characterized by means of nuclear magnetic resonance spectroscopy, ultrahigh-resolution ESI mass spectrometry, cyclic and square wave voltammetry and, in two cases, X-ray diffraction. The hydroxy functionalized macrocycle and the corresponding half-cycle stand out, as their intracyclic OHO hydrogen bonds stabilize their mixed-valent one- (, ) and three-electron-oxidized states ().

Geodesic-Planar Conjugates: Substituted Buckybowls-Synthesis, Photoluminescence and Electrochemistry.

C-C cross coupling products of bowl-shaped as-indaceno[3,2,1,8,7,6-pqrstuv]picene (Idpc) and different planar arenes and ethynyl-arenes were synthesized. Photoluminescence as well as electrochemical properties of all products were investigated and complemented by time-dependent quantum chemical calculations. UV/Vis spectroelectrochemistry investigations of the directly linked (Idpc) indicated the absence of any intramolecular charge-transfer transition of intermittently formed (Idpc) .

Ruthenium(II) Complex Containing a Redox-Active Semiquinonate Ligand as a Potential Chemotherapeutic Agent: From Synthesis to Studies.

Chemotherapy remains one of the dominant treatments to cure cancer. However, due to the many inherent drawbacks, there is a search for new chemotherapeutic drugs. Many classes of compounds have been investigated over the years to discover new targets and synergistic mechanisms of action including multicellular targets.

Increasing the Cytotoxicity of Ru(II) Polypyridyl Complexes by Tuning the Electronic Structure of Dioxo Ligands.

Due to the great potential expressed by an anticancer drug candidate previously reported by our group, namely, Ru-sq ([Ru(DIP)(sq)](PF) (DIP, 4,7-diphenyl-1,10-phenanthroline; sq, semiquinonate ligand), we describe in this work a structure-activity relationship (SAR) study that involves a broader range of derivatives resulting from the coordination of different catecholate-type dioxo ligands to the same Ru(DIP) core. In more detail, we chose catechols carrying either an electron-donating group (EDG) or an electron-withdrawing group (EWG) and investigated the physicochemical and biological properties of their complexes. Several pieces of experimental evidences demonstrated that the coordination of catechols bearing EDGs led to deep-red positively charged complexes - in which the preferred oxidation state of the dioxo ligand is the uninegatively charged semiquinonate.