Synthesis and Photochromic Properties of Naphthopyran Dimers

Abstract

We realized the synthesis of 2H-naphtho[1,2-b]pyran derivatives with substituents of halo, methyl at 6-position and/or, methyl, cyclopropyl, aryl at the 2-position in addition to three different spironaphtho[1,2-b]pyran derivatives with terpene substituents at the 2-spiro position of the pyran ring. The prepared naphtho[1,2-b]pyran derivatives 1a-c,2a-c,3a-c were subjected to dimerization in acetic acid with a few drops of concentrated sulfuric acid affording the corresponding dimers 4a-i. The structures of the dimers were confirmed based on the spectral tools (especially nuclear magnetic resonance). On exposure of the produced dimers to unfiltered light, a change from colorless to color state was observed. The effect of the substituent nature at the 2- or 6-positions of dimers on the photochromic properties and thermal fade characteristics was investigated