Dimers of pyrrolo-annelated indenofluorene-extended tetrathiafulvalenes – large multiredox systems

Novel scaffolds of indenofluorene (IF)-extended tetrathiafulvalenes (TTF) were synthesized starting from a new pyrrolo-annelated IF-TTF monomer. Rigid para- and meta-phenylene linked dimers were obtained via N-arylation reactions of the monomer, and their optical and redox properties were elucidated by UV-Vis absorption spectroscopy and cyclic and differential pulse voltammetries

Interaction-induced negative differential resistance in asymmetric molecular junctions

Combining insights from quantum chemistry calculations with master equations, we discuss a mechanism for negative differential resistance (NDR) in molecular junctions, operated in the regime of weak tunnel coupling. The NDR originates from an interplay of orbital spatial asymmetry and strong electron-electron interaction, which causes the molecule to become trapped in a non-conducting state above a voltage threshold. We show how the desired asymmetry can be selectively introduced in individual orbitals in e.g., OPE-type molecules by functionalization with a suitable side group, which is in linear conjugation to one end of the molecule and cross-conjugated to the other end.Comment: 8 page

Phosphite-mediated conversion of benzaldehydes into stilbenes via umpolung through a dioxaphospholane intermediate

AbstractThe phosphite-mediated coupling of two benzaldehydes into 2,2,2-triethoxy-1,3,2-dioxaphospholanes was investigated using 13C NMR spectroscopy and was found to be very sensitive to the nature of the ortho/para substituents, and promoted by electron-withdrawing groups (EWGs). Stilbene-extended tetrathiafulvalenes were prepared by heating the intermediate dioxaphospholane, containing aldehyde substituents at para positions and ethynyl groups at ortho/meta positions, with 1,3-dithiol-2-thiones in P(OEt)3. While EWGs promoted dioxaphospholane formation, electron-donating groups (EDGs), generated by conversion of the aldehydes into dithiafulvenes, promoted subsequent conversion into an alkene

Molecular solar thermal systems - control of light harvesting and energy storage by protonation/deprotonation

Molecular solar thermal (MOST) systems that undergo photoisomerizations to long-lived, high-energy forms present one approach of addressing the challenge of solar energy storage. For this approach to mature, photochromic molecules which can absorb at the right wavelengths and which can store a sufficient amount of energy in a controlled time period have to be developed. Here we show in a combined experimental and theoretical study that incorporation of a pyridyl substituent onto the dihydroazulene/vinylheptafulvene photo-/thermoswitch results in molecules whose optical properties, energy-releasing back-reactions and energy densities can be controlled by protonation/deprotonation. The work thus presents a proof-of-concept for using acid/base to control the properties of MOST systems

Subphthalocyanine-triangulene dyads: Property tuning for light-harvesting device applications

Organic photovoltaics relies on the development of stable chromophores and redox-active organic molecules with tailor-made HOMO/LUMO energies. Here, we present the synthesis and properties of novel dyads composed of boron subphthalocyanine (SubPc) and triangulene units, connected either at the peripheral position of the subphthalocyanine or at the axial boron. The connectivity has strong implications for the absorption and fluorescence properties of the dyads, as well as their redox properties. While the SubPc unit has a bowl shape, triangulene is a planar structural unit that allows dyads to dimerize in the solid state on account of π-stacking interactions as shown by X-ray crystallography of one of the dyads. The electronic properties were also studied computationally by density functional theory methods. Excellent agreement between experimental and computed data were obtained, showing that our computational method is a strong tool in the rational design of optimum molecules to ultimately obtain finely tuned molecules for device applications. Keywords: chromophores; conjugation; molecular engineering; redox‐active molecules; structure–property relationship