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A series of novel 2-and 5-naphtho[2,1-b]furyl fulgides with different combinations of substituents (H, Me, Et) in the furan ring and methylidene bridge were synthesized and their spectral, luminescent and photochromic properties were studied. The most sterically overcrowded ring-opened fulgides 4Z O and 14Z O under UV irradiation rearrange into the colored fluorescent ring-closed isomers C. The reverse dark reaction C®E O is not observed at room temperature over 48 h. The exposure of C forms to visible light results in the backward isomerization into the initial non-fluorescent form O. Thus, fulgides 4 and 14 represent photochromic compounds with modulated fluorescence which are sufficiently fatigue-resistant with respect to photodegradation, surviving at least ten cycles of photocoloration-photobleaching without notable decrease in the optical density at the absorption maximum of the cyclic form C.

2-Benzo[b]thienyl fulgides and fulgimides containing bulky diphenylmethylene substituents were synthesized in the form of their ring-opened E- or Z-isomers. In contrast to the majority of known fulgides/fulgimides, that form colored ring-closed structures under UV irradiation, the obtained compounds undergo an irreversible transformation leading to decoloration of their solutions. This rearrangement with the formation of the dihydronaphthalene core appeared to be by 2–3 orders of magnitude more efficient than for the known diphenylmethylene(aryl(hetaryl))fulgides. The molecular structures of E- and Z-isomers and of products of the photoinduced rearrangement completed by 1,5-H shift reaction, 3a,4-dihydronaphtho[2,3-c]furans(pyrroles) C, were established based on the data of 1H and 13C NMR spectroscopy and X-ray diffraction studies.

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