Substituted spirobenzopyrans

C. J. Roxburgh and P. G. Sammes, On the acid catalyzed isomerisation of some substituted spirobenzopyrans, Dyes Pigm., 27, 63-69 (1995). 

Therefore, the chemical linking of the dye molecules is only worthwhile if it results in a substantially better performance of the resulting materials. For the reasons discussed below, this is mainly expected for nonlinear optics (NLO) dyes. However, other dye-containing materials were also prepared by this approach. For example, new transparent photochromic hybrid materials were prepared by sol-gel processing of Si(OEt)4, sUanol-terminated dimethylsiloxane oligomers and triethoxysilylpropyl-substituted spirobenzopyranes, and fluorescent glasses and films from pyrene derivatives covalently tethered to RS103/2 (R = alkyl, phenyl) . 

Fig. 2. Stereoisomers of merocyanine derived from X-substituted l-alkyl-3,3-dimethylindolino-spirobenzopyran...

In solution, the thermal reversion of methacrylate polymers substituted with spirobenzopyrans was often accompanied by a spectral shift of the photomerocyanines and a deviation from first-order kinetics. These observations were ascribable to intermolecular interaction between the merocyanine form and the ester residue of methyl methacrylate. This was supported by the emergence of photoviscosity effects in solutions of these photochromic polymers. 

The V1/2 values obtained for dioxane solutions (10 4M) of spirobenzopyrans substituted on the chromene moiety are presented in Table 2. In the nitro-substituted spiropyran series (6, 28, and 29), the 6-nitro derivative is usually more stable. OCH3 and CHO substituents are also more stabilizing when on C6 (cf. 6 and 32 30 and 32). Indeed, the electron-donor efficiency of the methoxy group is higher when at C6 as indicated by the Hammett ct constant values, which are -0.76 for the C6 (para) position and -0.39 for the C8 (ortho) position. For the nitro-substituted spiropyrans, the electron-withdrawing character of N02 depends on the substitution position, with Hammett constants of 0.66, 0.78, and 0.80, for N02 at C7, C6, and C8, respectively. 

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