Spin alignment between the triplet excited state of phenylanthracene and the dangling verdazyl radical as studied by time-resolved electron spin resonance

The photo-excited quartet (S = 3/2) high spin state of a radical-excited triplet pair of a novel compound, phenylanthracene-verdazyl radical, was detected by time-resolved electron spin resonance (TRESR) technique. The TRESR spectrum was well analyzed by the ordinary spin Hamiltonian with the Zeeman and fine-structure terms. The g value, fire-structure splitting, and relative population of the Ms sublevels have been determined to be g = 2.0043, D = 0.0230 cm(-1), E = 0.0 cm(-1) and P(1/2), = P(-/2) = 0.5 and P(3/2) = P(-3/2) = 0.0, respectively, by the spectral simulation. The direct observation of the excited quartet state shows that the photo-induced intramolecular spin alignment is realized between the excited triplet state (S = 1) of the phenylanthracene moiety and the doublet spin (S = 1/2) of the dangling verdazyl radical.