Long-Range Ruthenium-Amine Electronic Communication through the para-Oligophenylene Wire

Abstract

The studies of long-range electronic communication are hampered by solubility and potential-splitting issues. A “hybridized redox-asymmetry” method using a combination of organic and inorganic redox species is proposed and exemplified to overcome these two issues. Complexes 1(PF6)–6(PF6) (from short to long in length) with the organic redox-active amine and inorganic cyclometalated ruthenium termini bridged by the para-oligophenylene wire have been prepared. Complex 6 has the longest Ru-amine geometrical distance of 27.85 Å. Complexes 3(PF6) and 4(PF6) show lamellar crystal packing on the basis of a head-to-tail anti-parallelly aligned dimeric structure. Two redox waves are observed for all complexes in the potential region between +0.2 and +0.9 V vs Ag/AgCl. The electrochemical potential splitting is 410, 220, 143, 112, 107, and 105 mV for 1(PF6) through 6(PF6), respectively. Ruthenium (+2) to aminium (N•+) charge transfer transitions have been identified for the odd-electron compounds 12+–62+ by spectroelectrochemical measurements. The electronic communication between amine and ruthenium decreases exponentially with a decay slope of −0.137 Å−1. DFT calculations have been performed to complement these experimental results.

Kinetic pathway for interfacial electron transfer from a semiconductor to a molecule

“…This suggests that electron transfer occurs by a 'hole'-transfer superexchange mechanism with the filled bridge orbitals. This mechanism is well established in purely molecular compounds and has recently been shown to support long-range electronic communication over distances of >27 Å through an oligophenylene bridge that provides an electronic coupling intermediate to that reported here for the xylyl-and phenylthiophene bridges 44 . Although there would be no kinetic advantage to hole superexchange through an oligophenylene bridge immobilized on semiconductor surfaces, the data reported here indicate that this bridge would also provide a pathway for electron transfer over large distances.…”

“…Prior reports and DFT analysis indicate that the direct oxidation or reduction of the bridge through a 'hopping mechanism' can be ruled out under these experimental conditions 44 . The lowestenergy bridge-dominated unfilled molecular orbitals are >3 eV, whereas the filled molecular orbitals are within 1 eV of the Ru III/II and TPA •+/0 reduction potentials.…”

Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment

“…16,17,19,[107][108][109] Additionally, cyclometalated bridging ligands enhance the electronic coupling between the redox centers in mixed-valent Ru/Ru complexes [110][111][112] and Ru/organic hybrid structures. [113][114][115][116] Despite the large variety of cyclometalated polypyridine ruthenium complexes synthesized up-to-date, however, no phosphorescence comparable to [Ru(bpy) 3 ] 2+ has yet been achieved. Furthermore, a general explanation for the striking difference in the luminescence Her key research interests comprise functional complex systems based on coordination and organometallic compounds with special emphasis on molecular wires, light-harvesting systems, bistable systems, emitters, switches and sensors as well as on (biomimetic) catalysts.…”

Transition from a Metal‐Localized Mixed‐Valence Compound to a Fully Delocalized and Bridge‐Biased Electrophore in a Ruthenium–Amine–Ruthenium Tricenter System

“…Such a connection mode ensures strong electronic coupling between the ruthenium and amine components. [24,25] …”

“…Each ruthenium component contains a RuÀC bond, which makes the Ru III/II potential comparable to the amine oxidation potential. [24,25] The bridging amine nitrogen atom is placed on the para position of the metalating phenyl ring with respect to the RuÀC bond. Such a connection mode ensures strong electronic coupling between the ruthenium and amine components.…”