Photochemistry of Tetrasulfur Tetranitride: Laser Flash Photolysis and Quantum Chemical Study

The photochemistry of tetrasulfur tetranitride (1) was studied in hexane solution by the laser flash photolysis technique (LFP). The experimental findings were interpreted E.A.; Gritsan, NP.; Bally, T.; Zibarev, A.V. Inorg. Chem. 2009, using the results of previous matrix isolation studies (Pritchina, 48, 4075) and high-level quantum chemical calculations. LFP produces two primary intermediates, one of which is the boatshaped 8-membered cyclic compound (2) and the other is the 6-membered S3N3 cyclic compound carrying an exocyclic (S)-N=S group (3). The primary products 2 and 3 absorb a second photon and undergo transformation to the 6-membered S3N3 cycle carrying an exocyclic (N)-S N group (4), which is very unstable and converts back to intermediate 3. The quantum yield of the primary product formation is close to unity even though the quantum yield of photodegradation of 1 is low (similar to 0.01). Thus, 1 is a photochromic compound undergoing in solution the thermally reversible photochemical isomerization. The mechanism of the photochromic process was established, and the rate constants of the elementary reactions were measured.