Methoxyl-induced fluorescence quenching in N,N′-bridged 9H-dipyrrinones and an X-ray crystal structure
作者:Sanjeev K. Dey、David A. Lightner
DOI:10.1007/s00706-008-0924-2
日期:2008.11
Strongly fluorescent dipyrrinones can be prepared by bridging the pyrrole and lactam nitrogens with a carbonyl group, from reaction with N,N'-carbonyldiimidazole in the presence of a strong, non-nucleophilic base. The yellow, N,N'-carbonyl-bridged dipyrrinones typically have fluorescent quantum yields (phi(F)) approaching 1.0. Thus, in chloroform, N,N'-bridged 9H-dipyrrinones with beta-alkyl substituents: 2,3-diethyl-7,8-dimethyl has phi(F) = 0.90 (lambda(em) = 465 nm) and 2,3-dimethyl-7,8-dimethoxy has phi(F) = 0.84 (lambda(em) = 482 nm). In contrast, 2,3-dimethoxy-7,8-dimethyl and 2,3,7,8-tetramethoxy show red-shifted lambda(em) but with strongly reduced phi(F): phi(F) = 0.10 (lambda(em) = 511 nm) and 0.08 (lambda(em) = 511 nm), respectively. Methoxy substituents on the lactam, but not the pyrrole ring act to quench the fluorescence and shift the emission and excitation wavelengths bathochromically. The first X-ray crystal structure of an N,N'-carbonyl-bridged dipyrrinone was obtained from 7,8-dimethoxy-2,3-dimethyl-10H-dipyrrin-1-one.