New 1,3-diazabicyclo-[3.1.0]hex-3-ene photochromic azo dyes: Synthesis, characterization and spectroscopic studies

Ten new 1,3-diazabicyclo-[3.1.0]hex-3-ene-based azo dyes (3a-3k) were synthesized via three-component reaction between [3-(x-phenyl)aziridin-2-yl](phenyl)methanone (x = 4-NO2, 3-NO2), NH4OAc and azo-coupled o-vanillin or salicylaldehyde precursors (1a-1e) and characterized by UV-Vis, IR and 1H NMR spectroscopic techniques. The synthesized azo dyes undergo ring opening in EtOH by irradiation with 254 nm UV light. The properties and photochromic structural behavior relationship (PSBR) of these dyes has been analyzed. The spectroscopic information show that the close-E photoisomer prevails in ordinary room light, however by irradiation with UV light the open-Z photoisomer is prominent.