Photochromic spin traps. Part IV. + 3,3-Diphenyl-5-[2-(N-tert-butylethanalnitrone)]-[3H]-naphtho[2,1-b]pyran

The title compound, a nitrone of the chromene series exhibiting photochromic properties, was synthesized and ESR studies proved its ability to act as a spin trapping agent. Although in general the aminoxyls formed in the trapping process did not exhibit any evidence of opening of the heterocyclic ring, both the closed and open forms have been observed for the spin adduct of the methyl radical. The rate constant for ring closure, i.e. the conversion of the latter isomer into the former upon ceasing optical excitation, was measured as 7 10?3 s?1 at 20 °C. The new photochromic nitrone did not exhibit a significant stabilizing effect towards Corn Yellow, a typical photochromic compound, but its action was synergistic to that of popular commercial additives.