Synthesis, Crystal Structure and Photochromic Property of a Dimeric Isofulgimide with an N-N Linkage

Isofulgimides, characterized by a 5-iminodihydrofuran-2(3H)-one moiety, constitute a subgroup of fulgide derivatives that have received comparatively limited attention despite their potential photochromic applications. Herein, we report the synthesis, crystal structure, and preliminary photochromic characterization of a structurally unique dimeric isofulgimide in which two conjugated systems are connected through a single N–N bond to form a more extensively conjugated system. The compound crystallizes in the centrosymmetric triclinic space group P-1, with disorder of the phenyl groups in close intermolecular contact and strong interactions, including strong π-π stacking. the molecular structure of each half of the dimer closely superimposes on that of the starting fulgide. In solution, irradiation with a low-power 405 nm laser produced a new broad absorption band centered at approximately 510 nm, indicating photoinduced isomerization. After irradiation was discontinued, this band gradually disappeared within approximately 42 min, demonstrating thermal recovery of the initial form. Because isofulgimides remain relatively uncommon and crystallographic studies of dimeric isofulgimides have not previously been reported, these findings provide new structural and preliminary photochemical insights into this understudied class of photochromic compounds.