Laser flash photolysis (LFP) of I-naphthyl azide in glassy 3-methylpentane at 77 K produces singlet 1-naphthylnitrene (362, 383, 397 nm), which relaxes to the lower energy triplet nitrene with k(isc) = (1.1 +/- 0.1) x 10(7) s(-1). LFP of 2-naphthyl azide under the same conditions fails to produce the corresponding singlet nitrene presumably due to rapid (k greater than or equal to 10(8) s(-1), 77 K) isomerization to an azirine. LFP of 1- and 2-naphthyl azides at ambient temperature produces the expected azirines which were detected by time-resolved infrared spectroscopy (1728 cm(-1) from 1-naphthylnitrene; 1724 cm(-1) from 2-naphthyinitrene) with lifetimes of 3.2 and 150 mus, respectively. Absolute bimolecular rate constants of reaction of the azirines with diethylamine in solution at ambient temperature were determined.