Sterically Protected N2O-Type Benzopyrromethene Boron Complexes from Boronic Acids with Intense Red/Near-Infrared Fluorescence

A series of N2O-type benzopyrromethene boron complexes have been synthesized from the condensation of pyrrole, formylisoindole, and various boronic acids. These dyes have red/near-infrared absorption, high solution- and solid-state fluorescence, as well as good solubility in a variety of solvents due to the presence of axial-substituted groups that provide steric protection and prevent their possible aggregations. Two water-soluble derivatives with pyridinium ions were developed as near-infrared excitable mitochondrially localizing fluorescent probes.