Triplet (diphenoxyphosphoryl)nitrene (3) was studied by solution phase laser flash photolysis, low-temperature absorption spectroscopy, and low-temperature EPR spectroscopy. In ethanol, an absorption maximum at 345 nm was observed upon laser flash photolysis of diphenyl phosphorazidate (1) and assigned to the triplet nitrene (r = 3.8 +/- 0.6 mu s). After irradiation of 1 in an EPA glass at 77 K, an absorption attributed to the triplet nitrene was observed at 336 am. The zero field splitting parameters from the EPR spectrum of the nitrene in EPA glass at 77 K were D/hc = 1.5408 cm(-1) and E/hc = 0.007 39 cm(-1). Stronger transient absorptions observed in hydroxylic solvents support the proposal that hydrogen bonding catalyzes intersystem crossing in nitrenes. [(a) Schuster, G. B.; Platz, M. S. In Advances in Photochemistry; Volman, D., Hammond, G., Neckers, D., Eds.; John Wiley and Sons : New York, 1992; Vol. 17. (b) Poe, R.; Grayzar, J.; Young, M. J. T.; Leyva, E.; Schnapp, K. A.; Platz, M. S. J. Am. Chem. Sec. 1991, 113, 3209. (c) Schnapp, K. A.; Platz, M. S. Bioconjugate Chem. 1993, 4, 178.]