Photochromic heterocyclic fulgides. Part 7. (E)-Adamantylidene-[1-(2,5-dimethyl-3-furyl)ethylidene]succinic anhydride and derivatives: model photochromic compounds for optical recording media

The thermally-stable coloured form 5a, obtained by irradiation (λ= 366 nm) of the title compound 4a, contains a rigid inflexible spiroadamantylidene group which results in a five- to nine-fold increase in the quantum efficiency for bleaching compared to the analogous compound 2 having methyl groups in the 7-position. The quantum efficiency for bleaching decreases with increasing wavelength of irradiation and increases with increasing temperature in a linear manner, and is solvent dependent.