Photoinduced Bimolecular Electron Transfer from CyanoAnions in Ionic Liquids.

Ionic liquids with electron-donatinganions are used to investigaterates and mechanisms of photoinduced bimolecular electron transferto the photoexcited acceptor 9,10-dicyanoanthracene (9,10-DCNA). Theset of five cyano anion ILs studied comprises the 1-ethyl-3-methylimidazoliumcation paired with each of these five anions: selenocyanate, thiocyanate,dicyanamide, tricyanomethanide, and tetracyanoborate. Measurementswith these anions dilute in acetonitrile and 1-ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)amide show that the selenocyanate andtricyanomethanide anions are strong quenchers of the 9,10-DCNA fluorescence,thiocyanate is a moderately strong quencher, dicyanamide is a weakquencher, and no quenching is observed for tetracyanoborate. Quenchingrates are obtained from both time-resolved fluorescence transientsand time-integrated spectra. Application of a Smoluchowski diffusion-and-reactionmodel showed that the complex kinetics observed can be fit using onlytwo adjustable parameters, Dand V0, where Dis the relative diffusioncoefficient between donor and acceptor and V0is the value of the electronic coupling at donor–acceptorcontact. [ABSTRACT FROM AUTHOR]