NEGATIVE PHOTOCHROMISM OF 3,1'-TRIMETHYLENE-BRIDGED 6-NITROINDOLINOSPIROPYRAN

A new photochromic nitroindolinospiropyran with a 3,1'-trimethylene bridge was synthesized. Different from the nonbridged spiropyrans it exists mainly as the colored twitter-ionic open form in polar solvents. The following values in CHCl3, DMSO, and CH3OH at 20 degrees C were determined: (1) molar absorption coefficient of the open form at lambda(max), (2) Arrhenius' activation energy, Delta G(double dagger) , Delta H-double dagger, and Delta S-double dagger of thermal coloring and bleaching, (3) Delta G, Delta H, and Delta S of the thermal coloring.