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 photochromi c properties, was synthesized and ESR studies proved its ability to act as a spin trapping agent. Although in general the aminoxyls formed in the trap ping process did not exhibit any evidence of opening of the heterocyclic ri ng, both the closed and open forms have been observed for the spin adduct o f the methyl radical. The rate constant for ring closure, i.e. the conversi on of the latter isomer into the former upon ceasing optical excitation, wa s measured as 7 x 10(-3) s(-1) at 20 degrees C. The new photochromic nitron e did not exhibit a significant stabilizing effect towards Corn Yellow, a t ypical photochromic compound, but its action was synergistic to that of pop ular commercial additives. Copyright (C) 2000 John Wiley & Sons, Ltd.