Photo‐Induced Discoloration and the Corresponding Mechanism of Benzotrifuroxan under UV Irradiation

Benzotrifuroxan (BTF) as a powerful and hydrogen-free explosive discolors under UV irradiation, but the process remains unclear. Herein, we comprehensively investigated the photochemical process and mechanism of BTF under UV irradiation. A pink color is observed in BTF after irradiation with 365-nm light, while BTF becomes brown by 254-nm light. Besides BTF, compound 1 is detected by ultrahigh-performance liquid chromatography after UV irradiation. Compound 1 is prone to be yielded under 254-nm irradiation compared to 365-nm irradiation. Meanwhile, it is easier for the formation of compound 1 in BTF solution rather than solid BTF. Additionally, a small amount of compound 2 is found in BTF solution after 254-nm irradiation over 120 min. A new photodegradation pathway of BTF is proposed through high-resolution mass spectrometry. Compound 1 is produced as the main product through the isomerization of the N-oxide of BTF, and BTF also loses NO to yield compound 2. Through the analysis of scanning electron microscopy, BTF exhibits different crystal structures between 365-nm irradiation and 254-nm irradiation. Nano holes are widely observed in solid BTF after 365-nm irradiation, but these holes disappear under 254-nm irradiation. Thus, the differences originating from the content of compound 1 and the crystal structure of BTF may lead to the discoloration of BTF under UV irradiation.