Photoinduced Bimolecular Electron Transfer in Ionic Liquids: Cationic Electron Donors

Abstract

Recently, we have reported a systematic study of photoinduced electron-transfer reactions in ionic liquid solvents using neutral and anionic electron donors and a series of cyano-substituted anthracene acceptors [ Wu , B. ; Maroncelli , M. ; Castner , E. W. Jr Photoinduced Bimolecular Electron Transfer in Ionic Liquids . J. Am. Chem. Soc. 139 , 2017 , 14568 ]. Herein, we report complementary results for a cationic class of 1-alkyl-4-dimethylaminopyridinium electron donors. Reductive quenching of cyano-substituted anthracene fluorophores by these cationic quenchers is studied in solutions of acetonitrile and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Varying the length of the alkyl chain permits tuning of the quencher diffusivities in solution. The observed quenching kinetics are interpreted using a diffusion-reaction analysis. Together with results from the prior study, these results show that the intrinsic electron-transfer rate constant does not depend on the quencher charge in this family of reactions.

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).…”

The excited-state dynamics of the radical anions of cyanoanthracenes

“…These compounds were selected for their widespread use as electron-accepting chromophores in bimolecular ET studies. [40][41][42][43][44][45][46][47] Combined with a strong electron donor, such as tetramethylphenylenediamine (TMPD), high ET driving forces, at which Marcus inverted region is expected, 48 can be achieved. As the ET fluorescence quenching of these cyanoanthracenes by TMPD was found to be diffusion limited, 45 it could possibly involve the electronic excited states of the ensuing radical ions.…”

Experimental measurement and prediction of ionic liquid ionisation energies

“…117,118 A pyridinium-based cation in an IL can act as an electron donor to a neutral dye solute. 119 This study demonstrates that the cation has been considered as an electron donor in ILs, but the full potential and importance has not yet been considered.…”