Solvent Tuning from Normal to Inverted Marcus Region of Intramolecular Electron Transfer in Ferrocene-Based Organic Radicals

Abstract

The solvent dependence of spectroscopic data of two neutral paramagnetic donor-acceptor dyads, based on a polychlorinated triphenylmethyl radical acceptor unit linked through a vinylene pi-bridge to a ferrocene (compound 1) or a nonamethylferrocene donor (compound 2) unit, is described. Both compounds exhibit broad absorptions in the near-IR region, with band maxima appearing around 1000 and 1500 nm for 1 and 2, respectively. These bands correspond to the excitation of a neutral DA ground state to the charge-separated D+A- state, indicative of an intramolecular electron-transfer process. Compounds 1 and 2 show two reversible one-electron redox processes associated with the oxidation of the ferrocene and the reduction of the polychlorotriphenylmethyl radical subunits. The solvent dependence of the redox potentials was also investigated, allowing the determination of the redox asymmetries DeltaG degrees of both dyads. The latter values, along with the experimental Eopt spectroscopic data, allow us to estimate, using the total energy balance Eopt = lambda + DeltaG degrees , the reorganization energy values, lambda, and their solvent polarity dependence. Since DeltaG degrees and lambda are of the same order of magnitude but exhibit opposite trends in their solvent polarity dependence, a unique shift from the normal to the inverted Marcus region with the change in solvent polarity is found. The kinetics of the charge recombination step of the excited charge-separated D+A- state was studied by picosecond transient absorption spectroscopy, which allows us to observe and monitor for the first time the charge-separated D+A- state, thereby confirming unambiguously the photoinduced electron-transfer phenomena.

Design of Perchlorotriphenylmethyl (PTM) Radical‐Based Compounds for Optoelectronic Applications: The Role of Orbital Delocalization

“…A paramagnetic and electronically switchable compound that has attracted a great deal of attention during the last decades in the field of molecular electronics and spintronics is the perchlorotriphenylmethyl (PTM) radical (see Figure ), with many derivatives studied in solution,,, crystals,,, under the form of Self‐Assembled Monolayers (SAMs),, or in molecular junctions ,,. These radical systems exhibit a high chemical and thermal stability and present very different electronic, optical, and magnetic properties compared to the corresponding closed‐shell or anionic forms.…”

Phase‐Transfer Catalysis in Oxidations Based on the Covalent Bonding of Hydrogen Peroxide to Amphiphilic Flavinium Salts

“…Ferrocene (Fc) and polyazine ruthenium complexes are two commonly used redox species for MV systems because of their well‐defined redox processes and the feasibility of structure modifications. In addition to symmetric structures,2, 7 redox asymmetric systems have also been well studied, as demonstrated by the early works of the groups of Taube,8 Henry,9 Sato,10 Meyer,11 and Long,12 as well as more recent works by Kaim,13 Low,14 Yuan,15 Liu,16 van Koten,17 Veciana,18 Winter,19 and Zhong,20 among others 21. However, studies on the changes of E op by a combined method of structure modification and solvent variation are limited.…”

Induced Self‐Assembly of a Tetrathiafulvalene‐Based Open‐Shell Dyad through Intramolecular Electron Transfer

“…Along the same research line we previously reported IET studies based on PTM dyads using ferrocenes as electron donor subunits in solution. [7] Moreover, the bistability phenomenon of one of these dyads in solid state was properly rationalized. [8] Here we focus on the study of the selfassembly of dyad 1 in solution induced by the associated IET process.…”