Synthesis and photochromism of naphtho[2,1-b]furyl fulgides

Abstract

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.