Synthesis, Structure, and Properties of β‑Vinyl Ketone/Ester Functionalized AzaBODIPYs from FormylazaBODIPYs

Postfunctionalization
of azaBODIPY (the BF2 complex
of azadipyrromethene) is highly desirable due to the strong tunable
absorption bands at wavelengths above 650 nm and the wide-ranging
applications of this class of dyes in biomedicine and materials science.
Currently available postfunctionalization methods for this class of
dyes have been limited to the Pd-catalyzed coupling reactions on β-halogenated
(brominated or iodinated) azaBODIPY platforms. In this work, we report
a new strategy for the facile postfunctionalization of the azaBODIPY
chromophore with various vinyl ketone and vinyl esters based on a
Wittig reaction on our previously developed β-formylazaBODIPYs
and our recently developed β-bromo-β′-formylazaBODIPYs.
Our strategy uses easily accessible starting materials and mild reaction
conditions. It is highly compatible with various common phosphonium
ylides (aliphatic, aromatic, and ester substituted ones). These resultant
bromo-containing β-vinyl ketone/ester functionalized azaBODIPYs
are potential photosensitizers and can be further functionalized via
coupling reactions. The ester groups on some of these resultant azaBODIPYs
can be further hydrolyzed to achieve the desired water solubility
and conjugate with the biomolecule and solid surface.