Magnetic field-enhanced photoinization of 6-methylpurine

The dominant features in the transient absorption spectra of 6-methylpurine (P) in aqueous solution, following laser excitation at 266 nm, are the triplet–triplet and the hydrated electron (eaq) absorption bands. Upon applying a weak magnetic field (H) of 234 G, the ionization yield increases 200%, whereas the population of triplet molecules remains the same, indicating that P is not ionized from the triplet manifold. Electronically excited P(S1) is the precursor of a geminate radical cation–electron pair 1{P+, e}, that evolves into an intermediate with triplet multiplicity 3{P+, e} that is sensitive to H and from which eaq is produced.