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Benzopyrans, photoreactions

The structural formula of l,2-dicyano-l,2-bis-(2,4,5-trimethyl-3thienyl)ethene, and 6-nitro-l, 3, 3 -trimethylspiro[2H-l-benzopyrane-2,2 -indoline], referred to here as DE and SP, respectively, and their photochemical isomers are shown in Figure 3.14. The DE and SP chromophores have two photochemical isomers, a stable isomer and a thermally unstable isomer, namely the open-ring and close-ring forms for DE and the spiropyran and photomerocyanine for SP. The stable and thermally unstable isomers are henceforth referred to here as the A and B isomers, respectively- Light irradiation produces photoreaction in both the A—>B and A< B directions, and the thermal reaction proceeds in the A<—B direction. In contrast to the colored photomerocyanine form, which usually fades after several minutes at room temperature, the colored close-ring form of DE is stable for more than three months at Both the A and B isomers of DE and SP can... [Pg.88]

As the geomeMcal structural changes are relatively small in the photochromic reactions, most of these reversible photoreactions could also proceed in the crystalline state. Thus, diarylethenes also exhibit crystalline state photochro-2.3 Benzopyran and naphthopyran (chromene) mism. Single crystals of the cocrystals with two or... [Pg.1989]


See other pages where Benzopyrans, photoreactions is mentioned: [Pg.353]    [Pg.170]    [Pg.162]    [Pg.88]    [Pg.250]    [Pg.820]    [Pg.170]   
See also in sourсe #XX -- [ Pg.355 ]




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