Magnetic field modulation of the delayed fluorescenceyield in the photoionization reaction of N, N, N′, N′‐tetramethyl‐p‐phenylenediamine in water

Abstract

Abstract. External magnetic field effects on the recombination fluorescence (MARY effect) in the photoionization reaction of N,N,N ,N -Tetramethyl-p-phenylenediamine (TMPPD) in water and DMSO/water mixture are studied. Relatively large magnetic field effects (MFE), ∼ 2-4%, on the fluorescence yield are observed in the extremely polar water solvent under magnetic fields as small as 3 mT. Such MFE is hardly expected in water due to instability and very fast escape of the solvated electron from the solvent cage. Enhancement in the signal-to-noise ratio and superior time resolution characterizing the technique of field modulation allowed the detection of a very short lived radical ion pair (about 1 ns). The observed MARY spectra illustrate that the singlet radical ion pair is more reactive than the triplet one.

Photoionization of TMPD in DMSO solution: mechanism and magnetic field effects

“…A particularly striking feature of figure 1(a), and of the observations by Grampp et al [13,14], is the unusually large Low Field Effect. It has been suggested that pronounced LFEs are expected, other things being equal, when one of the radicals has many large hyperfine couplings whilst its partner has hyperfine interactions that are few and small (i.e.…”

“…Moreover, the dependence of the TMPD fluorescence on the strength of the applied field should reflect the strength of the relevant internal magnetic interactions (hyperfine or dipolar). Previous studies [5,13,14] suggest that the RPM contribution is likely to dominate except, perhaps, when high yields of 3 TMPD result from intense pulsed laser irradiation.…”

“…UV irradiation of TMPD in a variety of solvents (alcohols, alcohol mixtures, dimethylsulphoxide (DMSO)/toluene mixtures) leads to the formation of a spin-correlated radical ion pair. As a consequence, the primary photochemistry can conveniently be studied using the magnetic field-dependence of the radical pair recombination kinetics and/or the reaction product yields [12][13][14].…”