Methoxyl-induced fluorescence quenching in N,N′-bridged 9H-dipyrrinones and an X-ray crystal structure

Strategic Construction of meso-Aryl-Substituted N,N-Carbonyl-Bridged Dipyrrinones as Small, Bright, and Tunable Fluorophores

“…Among them, boron dipyrromethene (BODIPY A , Figure a), which consists of a dipyrrolic fragment complexed with a boron center, has found applications in diverse areas such as fluorescence imaging, diagnostic and therapeutic reagents, and optoelectronic materials due to its ease of accessibility and derivatization, and tunable photophysical and chemical properties. − Consequently, considerable efforts have been devoted to developing new synthetic methods to expand the range of fascinating fluorescent dyes similar to the BODIPY π-systems . One intriguing but less explored strategy involves replacing BF 2 units with carbon as the bridging linker, resulting in a rigid 5.6.5 fused-ring system with excellent properties. − An elegant example of this is the successful synthesis of carbon-dipyrromethene ( B ) by Guo et al, which employed methylene to replace BF 2 units…”

“…Nonetheless, despite these breakthroughs, the development of CODPO fluorophores remains significantly constrained compared to BODIPY. The primary reason for this limitation is the synthetic challenges posed by restricted methods for the crucial precursor dipyrrinone E , which is currently mainly obtained through the base promoted condensation of premodified 2-formyl-1 H -pyrrole and pyrrolin-2-one (Figure b) . The synthesis of the above two starting compounds was notably complex and lengthy, resulting in low overall yields.…”

“…Inspired by our recent synthesis of cyclic BODIPY arrays, the essential precursor meso -phenyl substituted dipyrone 2a was obtained in a 76% yield from the hydrolysis of readily available α,α′-dichlorodipyrrin 1a in DMF with trifuoroacetic acid (TFA) at rt (Scheme a). Subsequently, following Lightner’s method, compound 2a was directly treated with 1,1′-carbonyldiimidazole (CDI) in the presence of 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU). However, this reaction produced a quite complex reaction mixture.…”