Fast photochromic molecules have attractive potential to apply to the ophthalmic lenses and realtime dynamic holography. However, the thermal decoloration reaction rate and the photoconversion efficiency of the photochromic molecules largely depend on their surrounding medium. Herein, we investigated the thermal decoloration behavior of fast photochromic 3Hnaphthopyrans in poly(methyl methacrylate)-b-poly(n-butylacrylate) (PMMA-b-PBA) block