The UV absorption spectra of B(N-3)(3), BCl(N-3)(2) and BCl2N3 isolated in low temperature argon matrices were measured as the matrices were photolyzed with the loosely focused output of a D-2 lamp. IR spectra were taken simultaneously with the UV spectra, and changes in the UV spectra were correlated with changes in the IR spectra. A series of bands at 348.0, 353.5, 360.0, 366.0, 372.5, and 379.5 nm appeared during the photolysis of B(N-3)(3) and were assigned as a vibrational progression in a bending mode of NNBN. Photolysis of BCl(N-3)(2) generated a feature at 408 nm that displayed evidence of vibrational structure and a sharp band at 275 nm. The 408 nm absorption was tentatively assigned to ClBN2, a three-membered ring compound, and the 275 nm band as the A(1)II <-- X(1)Sigma transition in BCl. No new UV features were observed during the photolysis of BCl2N3, although the IR spectrum clearly indicated the formation of ClBNCl. These data indicate that ClBNCl has no UV absorption spectrum at wavelengths longer than 240 nm.