Synthesis and photophysical characterization of a library of photostable halogenated bacteriochlorins: an access to near infrared chemistry

Near infrared (NIR) photons are ideally suited for photomedicine because they are relatively harmless and penetrate deeply in biological tissues. However, their use is impaired by lack of straightforward methods to synthesize large quantities of stable infrared-absorbing molecules with long-lived excited states. Here we present a one-step synthesis of amphiphilic meso-phenyl halogenated bacteriochlorins, via hydrazide reduction, possessing strong absorption about 750 nm. The reaction proceeds efficiently, in large quantities, with a solid-solid solvent-free methodology, that is characterized by its simplicity, efficiency and minimum environmental impact. The new bacteriochlorins have unprecedented chemical and photophysical properties, namely strong electronic absorption above 720 nm, adequate photostability, low fluorescence quantum yield and n-octanol/water partition coefficients (log POW) ranging from −1.7 to >4, meaning that the library of compounds synthesized in this work is versatile enough to be applied in photodynamic therapy for a range of biological targets.