Photoinduced Bimolecular Electron Transfer from Cyano Anions in Ionic Liquids

Abstract

Ionic liquids with electron-donating anions are used to investigate rates and mechanisms of photoinduced bimolecular electron transfer to the photoexcited acceptor 9,10-dicyanoanthracene (9,10-DCNA). The set of five cyano anion ILs studied comprises the 1-ethyl-3-methylimidazolium cation paired with each of these five anions: selenocyanate, thiocyanate, dicyanamide, tricyanomethanide, and tetracyanoborate. Measurements with these anions dilute in acetonitrile and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide show that the selenocyanate and tricyanomethanide anions are strong quenchers of the 9,10-DCNA fluorescence, thiocyanate is a moderately strong quencher, dicyanamide is a weak quencher, and no quenching is observed for tetracyanoborate. Quenching rates are obtained from both time-resolved fluorescence transients and time-integrated spectra. Application of a Smoluchowski diffusion-and-reaction model showed that the complex kinetics observed can be fit using only two adjustable parameters, D and V0, where D is the relative diffusion coefficient between donor and acceptor and V0 is the value of the electronic coupling at donor-acceptor contact.

Microscopic Structural and Dynamic Features in Triphilic Room Temperature Ionic Liquids

“…Additional details of our NMR diffusion protocols have been described previously (Liang et al, 2015; Wu et al, 2015, 2018).…”

Photoinduced Bimolecular Electron Transfer in Ionic Liquids: Cationic Electron Donors

“…Recent research into the mechanisms of electron-transfer reactions in ionic liquid (IL) solvents is focused on how the transport properties of the reactants and the solvation properties of the ionic liquids (ILs) determine the reaction kinetics. − The present work involves an extension of our recent investigations of reductive quenching of a series of cyanoanthracene fluorophores by an array of neutral and anionic electron donors . In the prior work, the measured differences in the electron donor diffusivities correlated with the observed quenching rates, which were interpreted on the basis of an analysis using the Marcus electron-transfer theory. , …”

Photodetachment and Electron Dynamics in 1-Butyl-1-methyl-pyrrolidinium Dicyanamide

“…The additional complexity of the multifaceted solvent time scales can have a substantial influence on the observed rates of bimolecular reactions. For example, charge transfer in the ionic liquids has been shown to occur at rates much faster than predicted by simple diffusion-limited models as a result of the interplay between transport- and distance-dependent rates of reaction. − Structural heterogeneity, characterized by X-ray scattering studies and molecular dynamics (MD) simulations, arises from charge and polarity ordering as a result of the neutral and charged components of the constituent ions. − Across these different nanometer-scale domains, solutes are subjected to different rates of diffusion and solvation motions. ,− The dynamics are complicated, with rates that vary in time and time scales that span decades. − In the presence of ionizing radiation, the initial events in the first few nanoseconds following the separation of charge, as electrons and intermediate species solvate and exhibit evolving reactivity, can have a significant impact on the time-integrated chemistry …”