The first example of triplet-state phosphoryl diradicals is reported. Photoinduced dissociative electron capture of two diastereoisomeric m-phenylenebis(ph0sphinic ch1oride)is in a glassy toluene matrix at 130 K using an electron-rich olefin affords the corresponding hosphoryl monoradicals and triplet-state diradicals in a 5:2 ratio. The triplet-state ESR spectrum gives zero-field parameters of IDlhcl = 0.0120 cm-' and IElhcl = 0.0015 cm-I. Variable temperature ESR experiments reveal Curie behavior for the Am, = 2 ESR signals between 3.8 and 100 K, consistent with a low-energy triplet state that either corresponds to the ground state or is degenerate with a singlet state. For the corresponding p-phenylene diastereoisomers, no triplet-state diradicals can be detected under identical experimental conditions and the ESR spectra only reveal the primary phosphoryl monoradicals and their protonated forms, as secondary species.