ABSTRACT
Boron-dipyrromethene dyes (BODIPYs) containing halogens at pyrrole carbons are very useful synthons for the synthesis of a variety of BOIDPYs for a wide range of applications. Among the functional groups, halogens are the functional groups which can be regiospecifically introduced at any desired pyrrole carbon of the BODIPY framework by adopting appropriate synthetic strategies. The halogenated BODIPYs can undergo facile nucleophilic substitution reactions to prepare several interesting BODIPY based compounds. This review describes the synthesis, properties and potential applications of halogenated BODIPYs containing one to six halogens at the pyrrole carbons of the BODIPY core as well as properties and applications of some of the substituted BODIPYs derived from halogenated BODIPYs.
ABSTRACT
A series of boron dipyrromethene (BODIPY) dyes containing two aldehyde functional groups at the 3 and 5 positions have been synthesized in low-to-decent yields in two steps. In the first step, the meso-aryl dipyrromethanes were treated with POCl(3) in N,N-dimethylformamide to afford 1,9-diformylated dipyrromethanes. In the second step, the diformylated dipyrromethanes were first in situ oxidized with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and then reacted with BF(3)·OEt(2) to afford 3,5-diformylboron dipyrromethenes. The X-ray structural analysis indicated that the aldehyde groups are involved in intramolecular hydrogen bonding with fluoride atoms, which may be responsible for the stability of the diformylated BODIPY compounds. The presence of two formyl groups significantly alters the electronic properties, which is clearly evident in downfield shifts in the (1)H and (19)F NMR spectra, bathochromic shifts in the absorption and fluorescence spectra, better quantum yields, and increased lifetimes compared to 3,5-unsubstituted BODIPYs. Furthermore, 3,5-diformylboron dipyrromethenes are highly electron-deficient and undergo facile reductions compared to unsubstituted BODIPYs. These compounds exhibit pH-dependent on/off fluorescence and thus act as fluorescent pH sensors.
