Molecular structure and photochromic properties of 1,3-dimethylindoline-3,3 '-alkano-2-spiro-2 '-(6 '-nitro)benzopyrans

Photochromic properties of spiroindolinobenzopyrans in which a -(CH2)(3)- or -(CH2)(5)- moiety links the 3-position of indoline and the 3'-position of benzopyran have been studied, In this regard, a photochromic color change was observed only when the -(CH2)(5)- bridging group was used. X-ray crystallographic data showed that the spiro-CO bond length in the pyran ring of the dye containing the -(CH2)(5) bridging group was slightly longer than that in the dye with th -(CH2)(3)-bridging group. X-ray data also suggest that extended conjugation in the open form of the dye containing the -(CH-(2))(3)-bridging group is inhibited because of the fixed conformation of the 6-membered ring. (C) 2002 Elsevier Science Ltd. All rights reserved.