| abstract |
Described herein are photochromic compounds or a structural isomer of the photochromic compound, the photochromic compounds represented by the formula: ##STR1## wherein R 1 , R 2 , R 4 , R 5 , R 6 , R 8 , A, B, C, and D are each selected from the group consisting essentially of hydrogen, a stable organic radical, a heterocyclic group, halogen, a nitrogen-substituted radical, and a nitrogen-substituted ring radical. |