The photochemistry of 2-thienylsulfonyl azide (1) and 3-thienylsulfonyl azide (6) has been disclosed by combining matrix-isolation spectroscopy with quantum chemical calculations. Two novel heteroaryl sulfonyl nitrenes, 2-thienylsulfonyl nitrene (2) and 3-thienylsulfonyl nitrene (7), have been generated during the 266 nm laser photolysis of 1 and 6, respectively. Both nitrenes in the triplet ground state have been characterized with matrix-isolation IR (N-15-labeling) in solid Ar (10.0 K), N-2 (10.0 K), and Ne (2.8 K) matrixes and EPR spectroscopy (2, vertical bar D/hc vertical bar = 1.452 cm(-1) and vertical bar E/hc vertical bar = 0.0058 cm(-1); 7, vertical bar D/hc vertical bar = 1.492 cm(-1) and vertical bar E/hc vertical bar = 0.0060 cm(-1)) in solid toluene at 5.0 K. Upon subsequent UV-light irradiation (365 nm), no Curtius rearrangement but decomposition of 2 occurs by SO2-elimination and the concurrent formation of ring-opening product (s-Z)-4-thioxo-2-buteneni- trile (3) via the intermediacy of the putative 2-thienylnitrene (4). In contrast, violet-light irradiation (400 +/- 20 nm) of 7 causes SO2-elimination to yield triplet 3-thienylnitrene (8), for which the IR spectroscopic identification is supported by quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) level. 3-Thienylnitrene is highly reactive, since it not only combines with SO2 to furnish 3-thienyl-N-sulfonylamine (9) but also undergoes ring-opening to (s-E)-4-thioxo-2-butenenitrile (10) under the UV-light irradiation (365 nm).