Thieno–Pyrrole‐Fused BODIPY Intermediate as a Platform to Multifunctional NIR Agents

We report the synthesis, photophysical and electrochemical properties, and in vivo fluorescence imaging of a series of new thieno–pyrrole-fused near-infrared (NIR) BODIPY agents by using a versatile intermediate as a building block. The versatile thieno–pyrrole-fused BODIPY intermediate was rationally designed to bear bromo-substituents and absorb in the mid-red region (635 nm) to act as an organic electrophile for the development of NIR multifunctional agents. The use of subsequent palladium-catalyzed and nucleophilic substitution reactions afforded highly conjugated NIR BODIPYs. The novel BODIPYs exhibit long-wavelength absorptions in the NIR region (650–840 nm). The agents produce sharp fluorescence bands, and most of them display respectable quantum yields of fluorescence (0.05–0.87) useful for biomedical imaging, as demonstrated by in vivo imaging with SBDPiR740. Interestingly, a number of agents in the series that are non-halogenated were reactive to O2 at the triplet photo-excited state coupled with a favorable redox potential and decent fluorescence, and hence could be potential candidates for use as photosensitizers in fluorescence-guided photodynamic therapy. Furthermore, the synthetic approach allows further functionalization of the highly conjugated NIR BODIPYs to tune the excited states (PET, ICT) and to conjugate targeting moieties for enhanced biological applications.