Laser flash photolysis detection of mono- and biradical mesitylene

Time-resolved transient absorption spectra have been obtained first for mesitylene by 355 nm laser flash photolysis at ambient temperature. Mono- and biradicals were observed in the experiment, in which the transient absorption peak at about 370 nm was assigned to the biradical and the peak at about 580 nm to the monoradical; the biradical has a longer lifetime than the monoradical. According to the representative value of the C-H bond dissociation energy for aromatic compounds monoradical formation might be a single-photon process. For comparison with the absorption spectra the time-resolved fluorescence spectra were obtained and also the biradical was assigned to about 393 nm.