Intensely fluorescent dipyrrinones

Intense fluorescence from a new, more highly conjugated (benzannelated) xanthoglow analog, 9,11‐ dimethyl‐10‐[2‐(methoxycarbonyl)ethyl]‐5 H ,7 H ‐pyrrolo[2′,1′:6,1]pyrimidino[3,4‐ a ]isoindole‐5,7‐dione ( 1 ), was determined accurately and compared with fluorescence from the parent xanthoglow, 1‐ethyl‐8‐[2‐(methoxycarbonyl) ethyl]‐2,7,9‐trimethyl‐3 H ,5 H ‐dipyrrolo[1,2‐ c :2′,1′‐ f ]pyrimidine‐3,5‐dione ( 2 ). Benzoxanthoglow ( 1 ) gave a quantum yield for fluorescence (ϕ F ) of 0.78 in cyclohexane (λ exc 412 nm, λ em 487 nm), whereas xanthoglow methyl ester ( 2 ) gave ϕ F  = 0.80 in cyclohexane (λ exc 410 nm, λ em 473 nm). In DMSO, 1 gave ϕ F  = 0.55 (λ exc 419 nm, λ em 530 nm) and 2 gave ϕ F  = 0.65 (λ exc 419 nm, λ em 508 nm), illustrating the large Stokes shifts and strong fluorescence properties of these easily synthesized yellow pigments. Copyright © 2004 John Wiley & Sons, Ltd.