Oxidative Coupling of 1,7,8-Unsubstituted BODIPYs: Synthesis and Electrochemical and Spectroscopic Properties

We report the synthesis of BODIPYs with unsubstituted
1,7,8-positions and their dimerization by oxidative coupling with
phenyliodine­(III)-bis­(trifluoroacetate) (PIFA). This dimerization
was achieved for BODIPYs substituted in the 3,5-positions with either
methyl or thienyl groups. The position and the type of the linkage
in the resulting dimers depended on the nature of the substituent.
The 3,5-dimethyl-BODIPY dyes were linked either via direct 1,1′-pyrrole–pyrrole
coupling or via a 1,3′-methylene bridge. The 3,5-dithienyl-BODIPY
dyes provided, in excellent yields, unique compounds linked exclusively
via the α-thienyl positions. All dyes were unreactive in the
8-position. Electrochemical and spectroscopic measurements on the
monomers and dimers provided evidence of interactions between the
two halves of the dimers. Thus, oxidation and reduction potentials
were split by up to 210 mV, and modest excitonic coupling and an internal
charge transfer were observed in some cases.