Abstract A combined matrix isolation FTIR and theoretical DFT/B3LYP/6-311++G(3df,3pd) study of the novel synthesised tetrazole-saccharyl conjugate 2-[1-(1 H -tetrazol-5-yl)ethyl]-1,2-benzisothiazol-3(2 H )-one 1,1-dioxide [1-TE-BZT] was performed. In the gas phase, at room temperature, the compound exists as a mixture of six isomeric forms (four conformers of 1 H tautomer and two conformers of 2 H tautomer). According to theoretical calculations, conformers 1 H were the most stable and the relative energies among the three most stable forms are lower than 4 kJ mol −1 . These conformers benefit from stabilising intramolecular hydrogen bonds-like interactions involving the 1 H of the tetrazole ring and the carbonyl oxygen of the saccharyl moiety. The photochemistry of 1-TE-BZT in solid argon was investigated and theoretical DFT/B3LYP/6-311++G(3df,3pd) calculations also helped in assignment of the experimental bands. A quick consumption of the compound occurred after irradiation of the matrix with UV laser light at λ = 275 nm. Three photofragmentation pathways were proposed, one leading to 2-[1-(1 H -diaziren-3-yl)ethyl]-1,2-benzisothiazol-3(2 H )-one 1,1-dioxide and molecular nitrogen, a second one giving 2-(1,1-dioxide-3-oxo-1,2-benzisothiazol-2(3 H )-yl)propanenitrile and azide, and a third one involving loss of azide from the tetrazole ring and decarbonylation of the saccharyl ring of 1-TE-BZT to give acrylonitrile and 7-thia-8-azabicyclo[4.2.0] octa-1,3,5-triene 7,7 dioxide. The comparison of the relative intensities of the bands of the photoproducts obtained from the three channels allowed us to consider the latter pathway, involving an unprecedented photocleavage of the benzisothiazole (saccharyl) ring, as the preferred photodegradation channel of 1-TE-BZT.