Synthesis and Photochromism of <i>2H</i> ‐Naphthopyrans With an Extended Conjugation Skeleton

Abstract Two series of new 2H‐naphthopyran derivatives with an extended conjugation skeleton—benzonaphthopyrans ( BNPs ) and naphthonaphthopyran ( NNPs )—have been designed and synthesized in this work. Their photochromic properties in organic solution and in poly(methyl methacrylate) (PMMA) have been investigated with special attention on the relationship between the extended conjugation skeleton and the photochromism. Compared to the simple benzopyran ( BP ) and the parent 2 H ‐naphthopyran (NP), both BNPs and NNPs exhibit much better photochromic properties, such as faster photo‐responsive and thermal fading rates, and excellent fatigue resistance, which indicates the extended conjugation skeleton can significantly improve the photochromic properties of 2 H ‐naphthopyran derivatives. This is a new strategy to develop photochromic 2 H ‐naphthopyrans with potential applications in fields such as ophthalmic lenses and photo‐information storage.