Photochromic benzo[g]indolyl fulgimide with modulated fluorescence

Abstract

A new photochromic fulgimide, (E)-1-(anthracen-9-ylmethyl)-3-[1-(5-methoxy-2-methyl-1-phenyl-1H-benzo[g]indol-3-yl)ethylidene]-4-(propan-2-ylidene)pyrrolidine-2,5-dione, has been synthesized and found to exhibit fluorescence. The structure of this compound and intermediate fulgenates and amidofulgenic and fulgenic acids has been determined by electronic and vibrational spectroscopy, ¹H and ¹³C NMR, and mass spectrometry. The amidofulgenic and fulgenic acids are capable of undergoing photoinduced reversible Z/E isomerization with respect to the C=C bond without subsequent cyclization, whereas fulgenates are converted to the corresponding cyclic structures. The new fluorescent fulgimide is transformed into the colored nonfluorescing cyclic isomer under UV irradiation. The reverse ring opening under visible light irradiation restores the fluorescence properties, which makes this compound a molecular fluorescence switch.