2,3-Bis(diphenylmethylene)succinic Anhydride, (I), 2-(2-Adamantylidene)-3-(9-fluorenylidene)succinic Anhydride, (II), and 2-(9-Fluorenylidene)-3-(3,4,5-trimethoxybenzylidene)succinic Anhydride, (III)

The title compounds are derivatives of dimethylenesuccinic anhydride and belong to the fulgide family of compounds. The fulgides were the first photochromic systems to be discovered. Fulgide (I) (C₃₀H₂₀O₃) possesses a crystallographic twofold axis. The divinylsuccinic anhydride moiety is not planar in fulgides (II) (C₂₇H₂₂O₃) and (III) (C₂₇H₂₀O₆). In both (II) and (III), the C atom bonded to the fluorenyl moeity deviates significantly from the mean plane through the five-membered ring of the fluorenyl moiety.

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