Photodegradation of Flutamide and Halogen Derivatives of Nitrobenzotrifluoride: The NO Release Channel.

The photodegradation of the nonsteroidal antiandrogen drug flutamide has been long linked to the photoisomerization involving the nitro group. In this work, the dynamics of NO photoelimination upon photolysis at 266 nm of flutamide, nitrobenzotrifluoride, and its halogen derivatives were investigated. Similar to nitrobenzene and its derivatives, a bimodal translational energy distribution was observed for the NO photofragment indicating the presence of two distinct elimination channels resulting in slow and fast components. The trends in the slow/fast branching ratio show that halogen substitution at the para position increases the triplet state yield due to the internal heavy-atom effect leading to enhancement of the fast component. Furthermore, the topology of the triplet state potential energy surface showed that the minimum energy path favors the oxaziridine ring-type intermediate over the NO 2 roaming mechanism in all five molecules investigated. The steric interaction between the NO 2 group and the CF 3 group, which are placed in the ortho position, lowers the barrier for the formation of the oxaziridine transition state compared to that of nitrobenzene.