A photochromic compound including a core skeletal structure represented by the following Formula (I), wherein D is oxygen or sulfur; E is oxygen, sulfur, or NR2′; a is 0 or 1; R1 is hydrogen, or substituted or unsubstituted alkyl; R2 and R2′ are each independently selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, or substituted or unsubstituted heterocycloalkyl; and the photochromic compound is a thermally reversible photochromic compound.