Tetrahedral boron chemistry for the preparation of highly efficient "cascatelle" devices.
The replacement of the two fluorine atoms on the boron center of the well-known Bodipy fluorophore by functionalized acetylenic groups opens the way to a new family of highly luminescent, redox active, and stable fluorophores termed "E-Bodipy" species. The substitution is effective for ethynyl-lithium reagents incorporating tolyl, naphthyl, pyrenyl, fluorenyl, and terpyridinyl units. The protocol also tolerates the presence of various functional groups in the dipyrromethene meso position such as pyrene, phenylethynylpyrene, 4'-terpyridine, and iodophenyl. The last of these is particularly useful for a further coupling reaction enabling introduction of a flexible arm bearing a succinimidyl unit reactive toward primary amines. X-ray structure determinations of two E-Bodipy compounds confirm the introduction of the ethynyl units and show the boron atoms to have a distorted tetrahedral environment, with B-C(ethynyl) approximately 1.59 A and both boron atoms lying essentially in the mean planes of the dipyrromethene units. All the new compounds show intense electronic absorption bands (epsilon 60,000-70,000 M-1 cm-1), high quantum yields (>80%), and slow rates of nonradiative decay. Absorption by the aromatic substituents results in a "cascatelle" process leading to emission exclusively through the boradiazaindacene entity and thus large virtual Stokes' shift (>10,000 cm-1). The new compounds are also redox active, with the formation of both Bodipy+* and Bodipy-* occurring more readily than for F-Bodipy species. The molecules in their excited states are strong reducing agents.
Goze
Christine
C
Laboratoire de Chimie Moléculaire, Centre National de la Recherche Scientifique (CNRS), Ecole de Chimie, Polymères, Matériaux (ECPM), 25 rue Becquerel, 67087 Strasbourg Cedex 02, France.
Ulrich
Gilles
G
Ziessel
Raymond
R
D001896:Boron Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D013050:Spectrometry, Fluorescence
C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D005456:Fluorescent Dyes