Cage lifetimes of ionic liquids as studied by the magnetic field effect probe

Abstract

Magnetic field effects (MFEs) on the photoinduced hydrogen abstraction reaction of benzophenone with phenol were investigated in ionic liquids (ILs) with a short alkyl chain (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA TFSA)) and long alkyl chains ((N,N,N-trimethyl-N-octylammonium bis(trifluoromethanesulfonyl)amide (TMOA TFSA) and N-decyl-N,N,N-trimethylammonium bis(trifluoromethanesulfonyl)amide (DTMA TFSA)) by a nanosecond laser flash photolysis technique. In each ionic liquid, escaped radical yield of a benzophenone ketyl radical rapidly increased with increasing magnetic field strength (B) of 0 T < B≤ 0.01 T. At 0.01 T < B≤ 0.4 T, the escaped radical yield almost saturated in TMPA TFSA or gradually increased in TMOA TFSA and DTMA TFSA. At much higher fields of 0.4 T < B≤ 30 T, the yield gradually decreased, resulting in 10-15% decrease at 30 T. The observed MFEs can be explained by the hyperfine coupling and Δg mechanisms together with the relaxation mechanism. On the time profiles of the transient absorption observed for the benzophenone ketyl radical, MFEs were generated in the time range of 0 < t < 0.6 μs. The cage lifetimes of TMOA TFSA and DTMA TFSA were estimated to be at least 120 ns.

Diffusion and Solvation of Radical Ions in an Ionic Liquid Studied by the MFE Probe

“…In TMPA TFSA, the cage lifetime was estimated to be shorter than 20 ns from the generation dynamics of the MFE with the neutral RP. 54 In the present study, the estimated τ cage value of 170 ns is much longer than that obtained for the neutral RP in TMPA TFSA. The difference in τ cage values suggests that the solvation dynamics of the charged molecules are largely different from that of neutral molecules in the IL.…”

A practical approach to calculate the time evolutions of magnetic field effects on photochemical reactions in nano-structured materials

“…A magnetic field can change the populations of the singlet and the triplet RPs therefore affecting the recombination reaction of RPs quantum mechanically. Recently we discussed the solute molecular diffusions in mesoporous silicates of MCM-41 12 and in ionic liquids [13][14][15][16][17][18][19] from the observations made of the MFEs on the photochemical reactions. In contrast, the recombination reactions proceed efficiently in the contact RPs.…”

Local structure of ionic liquids probed by self-quenching of thiobenzophenone

“…In addition, results from the MFE probe measurements with analyses by the stochastic Liouville equation (SLE) show that TMPA TFSA has a local structure with a radius of about 2 nm [30][31]33 and a lifetime of at least 17 ns. 34 Such a local structure is analogous to the cage-like structure found in micellar solutions. To further investigate this possibility, we extended the study of self-quenching of 3 TBP* to an SDS micellar solution, which is known to have a similar cage size to TMPA TFSA.…”

“…Using another experimental technique, MFE probe, we recently studied the cage lifetimes of ILs which have short and long alkyl chains; TMPA TFSA, N,N,N,-trimethyl-N-octylammonium bis(trifluromethanesulfonyl)amide (TMOA TFSA), and N-decyl-N,N,N,-trimethylammonium bis(trifluromethanesulfonyl)amide (DTMA TFSA). 34 MFEs on the photoinduced hydrogen abstraction reactions of BP with phenol were investigated by nanosecond laser flash photolysis. MFEs were generated in the time range of several tens of ns (in TMPA TFSA) to hundreds of ns (in TMOA TFSA and DTMA TFSA) after laser excitation.…”

“…We have also studied the nanoscale ordering structures of ILs by the magnetic field effect probe (MFE probe). [27][28][29][30][31][32][33][34] Strong coulombic interactions and the aggregation of nonpolar regions of ILs can lead to nanoscale ordering structures, which may resemble micelles. Micelles are known to form from detergent molecules that possess both polar and nonpolar moieties.…”