Boron-dipyrromethene dyes for incorporation in synthetic multi-pigment light-harvesting arrays

The synthesis of light-harvesting arrays requires modular pigment building blocks. Boron-dipyrromethene dyes are well-suited for the photochemical sensitization of free base or metalloporphyrins. Direct access to boron-dipyrromethene dyes bearing reactive substituents is provided by a simple synthetic route involving two one-flask reactions. Reaction of pyrrole or 2-methylpyrrole with an aldehyde under gentle acid catalysis affords the corresponding dipyrromethane. Subsequent oxidation (DDQ or p-chloranil) and complexation affords the dye. Boron-dipyrromethene dyes bearing iodo- or ethynyl-phenyl substituents at the meso-position have been prepared as modular components for building block applications. These dyes are stable, accessible, and have suitable spectroscopic features for use as porphyrin accessory pigments in light-harvesting arrays.