Electron Transfer around a Molecular Corner

Abstract

The distance dependence of electron transfer (ET) is commonly investigated in linear rigid rod-like compounds, but studies of molecular wires with integrated corners imposing 90° angles are very rare. By using spirobifluorene as a key bridging element and by substituting it at different positions, two isomeric series of donor-bridge-acceptor compounds with either nearly linear or angled geometries were obtained. Photoinduced ET in both series is dominated by rapid through-bond hole hopping across oligofluorene bridges over distances of up to 70 Å. Despite considerable conformational flexibility, direct through-space and through-solvent ET is negligible even in the angled series. The independence of the ET rate constant on the total number of fluorene units in the angled series is attributed to a rate-limiting tunneling step through the spirobifluorene corner. This finding is relevant for multidimensional ET systems and grids in which individual molecular wires are interlinked at 90° angles.

Dual Nickel-/Palladium-Catalyzed Reductive Cross-Coupling Reactions between Two Phenol Derivatives

“…GC-MS analysis was conducted on Agilent 5977B GC/MSD instrument equipped with a HP-5MS UI column (30 m  0.25 mm). 1 H NMR, 13 C NMR and 19 F NMR spectra were recorded at 400 MHz, 101 MHz and 376 MHz, respectively in CDCl3 (or DMSO-d6) at room temperature. 1 H NMR was reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quadruplet, m = multiplet), coupling constant (J values) in Hz and integration.…”

“…A change in reaction temperature of +/-5 °C only had a small impact on the yields (entries [15][16]. Finally, a range of other polar solvents were shown to decrease the yield of the desired cross-coupling product (entries [17][18][19][20].…”

“…The presence of various common aliphatic functional groups such as ether, ketones, nitrile, and ester did not affect the reaction outcome, and high yields were obtained (13)(14)(15)(16)(17). An aryl fluoride and even an aryl chloride were well-tolerated (18)(19). Substrates containing an aryltrimethylsilyl group and a dihydrobenzofuran could also undergo the reductive crosscoupling reaction (20)(21).…”

Shortcuts for Electron‐Transfer through the Secondary Structure of Helical Oligo‐1,2‐Naphthylenes

“…The choice of triarylamine( TAA) and [Ru(bpy) 3 ] 2 + as electron-donor and electron-acceptor units was mainly motivatedb yt heir favorable electrochemical andoptical spectroscopic properties, providing unambiguous observables in time-resolved laser spectroscopy. [6,13] As pace-filling molecular model of the dyad with n = 3 (Scheme 2b)i llustrates the steric congestion caused by the 1,2-naphthylene based wire backbone, and it becomes evident that pathways involving noncovalent contacts can potentially contribute to electron transfer between TAAa nd [Ru(bpy) 3 ] 2 + in such structures. To some extent,t he situation in our dyads resembles that encountered in proteins, in which electron transfer along the covalent primary structure is often preferable, but in which individual steps involving noncovalent contacts across the tertiary structure can make important contributions.…”

“…Quantitative information on electron transfer pathways is often extractable from distance dependence studies of electron transfer rates, and therefore, we synthesized three donor–acceptor dyads (Scheme a) comprised of variable‐length 1,2‐naphthylene bridges ( n =1, 2, 3). The choice of triarylamine (TAA) and [Ru(bpy) 3 ] 2+ as electron‐donor and electron‐acceptor units was mainly motivated by their favorable electrochemical and optical spectroscopic properties, providing unambiguous observables in time‐resolved laser spectroscopy . A space‐filling molecular model of the dyad with n =3 (Scheme b) illustrates the steric congestion caused by the 1,2‐naphthylene based wire backbone, and it becomes evident that pathways involving noncovalent contacts can potentially contribute to electron transfer between TAA and [Ru(bpy) 3 ] 2+ in such structures.…”