Spiropyrans as Vapor-Deposited and Amorphous Films

Vacuum-deposited films of 6-nitroBIPS having in the l -position -alkyl chains of 1, 7, 12, and 18 carbon atoms are amorphous and colorless, but crystallize upon standing. The films color with UV exposure, and the colored film bleaches upon exposure to visible light. 

6-NitroBIPS having in the 5 -position (4 -X-benzoyloxy)-benzylidenamino substituents (128), where X is cyano, methoxy, and n-hexoxy, form amorphous films exhibiting birefringence when colored. The bulk materials exhibit quasi-liquid crystalline properties, intermediate between supercooled liquids and mesophases, which are attributed to the interactions between small ordered domains of the spiropyran molecules.149 

In another alternative to the simple evaporation of 6-nitroBIPS, a plasma polymerization process was used to prepare a highly adherent, smooth, transparent film having good photochromic properties. However, after 1 week of storage, the film lost its photochromic properties, probably through crystallization.152 

The photocoloration and photobleaching behaviors of vacuum-deposited and spin-coated poly(methyl methacrylate) films of 6-hydroxyBIPS, and of the 6-nitroBIPS having 1, 7, 12, and 18-carbon alkyl chains on the indoline N atom, were studied at 50K. The 6-hydroxy BIPS was photobleached both in deposited and cast 

Three spiropyrans, each molecule having a long alkyl chain located in a different relative position (l -hexadecyl, 3-decyl, and 8-dodecanoyloxymethyl), were spread as monolayers on water under irradiation and the changes of surface area and surface pressure with time were measured both when the lamp was turned on and after it was turned off. The results were especially striking observations of a reversible and an irreversible photoconversion of a surface-inactive system into a surface-active one.154 

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