Not So Innocent After All: Interfacial Chemistry Determines Charge-Transport Efficiency in Single-Molecule Junctions.

Most studies in molecular electronics focus on altering the molecular wire backbone to tune the electrical properties of the whole junction. However, it is often overlooked that the chemical structure of the groups anchoring the molecule to the metallic electrodes influences the electronic structure of the whole system and, therefore, its conductance. We synthesised electron-accepting dithienophosphole oxide derivatives and fabricated their single-molecule junctions. We found that the anchor group has a dramatic effect on charge-transport efficiency: in our case, electron-deficient 4-pyridyl contacts suppress conductance, while electron-rich 4-thioanisole termini promote efficient transport. Our calculations show that this is due to minute changes in charge distribution, probed at the electrode interface. Our findings provide a framework for efficient molecular junction design, especially valuable for compounds with strong electron withdrawing/donating backbones

Mesure de distances nanométriques entre deux complexes de manganèse par PELDOR (Pulsed Electron-Electron Double Resonance) à haut champ

In this work, the synthesis of a set of platforms that incorporate a central linker of varying length connected to two high-spin MnII complexes has been performed. Several ligands were screened and efficient synthetic methodologies were developed to graft them on various spacers covering the 1.5 – 5.5 nm range. The Mn-Mn distance has been successfully measured using high-field pulsed electron paramagnetic resonance (EPR) spectroscopy, more precisely pulsed electron-electron double resonance (PELDOR). We showed that the use of MnII complexes with low zero-field splitting (ZFS) parameters led to an improved sensitivity. For flexible polyproline-based platforms, distances and distribution profiles obtained with PELDOR were in good agreement with molecular dynamics (MD) estimations, but additional features in the distance distributions could be observed under specific conditions. These finding were rationalized by taking into account the pseudo-secular term of the dipolar Hamiltonian, which was found to be non-negligible for the studied platforms, where pumped and detected spins are very similar. When the linker was rigid, the influence of the pseudo-secular interaction was much more prominent, leading to distance profiles with a higher width than predicted by MD calculations. Other emergent spin labels for pulsed EPR-based distance measurements such as persistent substituted trityl radicals were studied and their g-tensor was accurately measured using high-field EPR with MnII as an internal reference. Density functional theory (DFT) calculations were performed to understand the relationship between the structure and the EPR properties of the studied trityl radicals.Au cours de ce travail, une série de plateformes constituées d'un espaceur central connecté à deux complexes de MnII à haut spin a été synthétisée. De nombreux ligands ont été étudiés et greffés sur un ensemble d'espaceurs de longueur variant entre 1,5 et 5,5 nm. La distance Mn-Mn a été mesurée avec succès par résonance paramagnétique électronique (RPE) impulsionnelle à haut champ en utilisant la méthode PELDOR (Pulsed Electron-Electron Double Resonance). L'emploi de complexes de MnII avec de faibles valeurs d'éclatement en champ nul (ECN) a permis d'améliorer la sensibilité de cette méthode. Pour les plateformes constituées d'un espaceur polyproline, un bon accord a été observé entre la distribution de la distance Mn-Mn obtenue par PELDOR et par dynamique moléculaire, mais des composantes plus courtes dans la distribution ont été détectées pour certains paramètres expérimentaux. Ces observations ont été rationalisées en tenant compte du terme pseudo-séculaire de l'Hamiltonien dipolaire, non négligeable pour les systèmes étudiés où les spins observés et détectés sont similaires. Lorsqu'un espaceur rigide est employé, l'interaction pseudo-séculaire est bien plus marquée, ce qui se traduit par une distribution de distances plus large que prévu par la dynamique moléculaire. L'étude de nouveaux centres paramagnétiques pour la méthode PELDOR comme les radicaux trityl persistants a également été entreprise. Le tenseur g de ces radicaux a été déterminé avec précision par RPE à haut champ en utilisant MnII comme référence. Des calculs de DFT (Density Functional Theory) ont été effectués pour comprendre la relation entre la structure et le spectre RPE de ces radicaux trityl

Highly Luminescent 4-Pyridyl-Extended Dithieno[3,2-b:2′,3′-d]phospholes

The unexpectedly challenging synthesis of 4-pyridyl-extended dithienophospholes is reported. The optical and electrochemical properties of the phosphoryl-bridged species were studied experimentally and computationally, and their properties compared to their non-P-bridged congeners. The 4-pyridyl-extended dithieno-phospholes display quantitative luminescence quantum yields in solution.<br /

Fluorescence-based Measurement of the Lewis Acidities of Lanthanide Triflates in Solution

Despite the prominence of rare earth complexes to act as Lewis-acid catalysts in organic synthesis, the comprehensive measure of the Lewis-acid strength of such compounds has yet to be performed due to incompatibilities with existing methods. We report our results in measurement of a sequence of lanthanide triflates via our recently established Fluorescent Lewis adduct (FLA) method. The persistence in solution of these Lewis acids as solvated coordination complexes is accurately measurable by the FLA method. However, several of the RE species exhibit fluorescence quenching, which may potentially inhibit the measurement. Nevertheless, meaningful FLA measurements were still able and the results correspond to both periodic trends and were even consistent with previous correlated reported dat

Nanoparticles under the light: click functionalization by photochemical thiol-yne reaction, towards double click functionalization.

International audienceA light click away: The first application of the thiol-yne reaction to nanoparticle functionalization is described (see figure). This metal-free click chemistry approach is compatible with the addition of various molecules at the surface and can be combined with CuAAC methodology to perform chemoselective double functionalization

Synthesis of Homoditopic Ligands with an Incrementable Rodlike Backbone

International audienc

CCDC 1896018: Experimental Crystal Structure Determination

BODCAB : 26,28,30,32,34-pentamethoxyhexacyclo[21.2.2.23,6.28,11.213,16.218,21]pentatriaconta-1(25),3,5,8,10,13,15,18,20,23,26,28,30,32,34-pentadecaene-4,9,14,19,24-pentayl pentakis[4-(phenyldiazenyl)phenyl] pentakis(sulfate) unknown solvate Space Group: P 1 (2), Cell: a 15.5126(5)Å b 17.6739(5)Å c 18.9334(6)Å, α 99.421(3)° β 92.842(3)° γ 92.615(2)

CCDC 1904736: Experimental Crystal Structure Determination

BODJAI : 2,2',2'',2''',2''''-{[26,28,30,32,34-pentamethoxyhexacyclo[21.2.2.23,6.28,11.213,16.218,21]pentatriaconta-1(25),3,5,8,10,13,15,18,20,23,26,28,30,32,34-pentadecaene-4,9,14,19,24-pentayl]pentakis(oxy)}penta-acetonitrile unknown solvate Space Group: P 1 (2), Cell: a 12.1203(2)Å b 13.2138(2)Å c 17.0854(3)Å, α 89.7350(10)° β 81.9010(10)° γ 75.3150(10)

CCDC 1896023: Experimental Crystal Structure Determination

BODCIJ : 4,9,14,19,24-pentamethoxy-26,28,30,32,34-pentaphenylhexacyclo[21.2.2.23,6.28,11.213,16.218,21]pentatriaconta-1(25),3,5,8,10,13,15,18,20,23,26,28,30,32,34-pentadecaene unknown solvate Space Group: P c a 21 (29), Cell: a 25.0851(7)Å b 20.5287(6)Å c 22.3174(4)Å, α 90° β 90° γ 90

CCDC 1904933: Experimental Crystal Structure Determination

BODJEM : 26,28,30,32,34-pentakis([1,1'-biphenyl]-4-yl)hexacyclo[21.2.2.23,6.28,11.213,16.218,21]pentatriaconta-1(25),3,5,8,10,13,15,18,20,23,26,28,30,32,34-pentadecaene-4,9,14,19,24-pentol acetone unknown solvate Space Group: P 1 (2), Cell: a 16.63130(10)Å b 19.13610(10)Å c 25.19360(10)Å, α 94.5000(10)° β 96.8560(10)° γ 98.2260(10)° BODJEM : 26,28,30,32,34-pentakis([1,1'-biphenyl]-4-yl)hexacyclo[21.2.2.23,6.28,11.213,16.218,21]pentatriaconta-1(25),3,5,8,10,13,15,18,20,23,26,28,30,32,34-pentadecaene-4,9,14,19,24-pentol acetone unknown solvate Space Group: P 1 (2), Cell: a 16.63130(10)Å b 19.13610(10)Å c 25.19360(10)Å, α 94.5000(10)° β 96.8560(10)° γ 98.2260(10)