Conjugated BODIPY Oligomers with Controllable Near-Infrared Absorptions as Promising Phototheranostic Agents through Excited-State Intramolecular Rotations

Conjugated
molecules with coplanar strong donor and acceptor (D-A)
units have been widely used in the design of near-infrared (NIR) photothermal
agents to increase an absorption band through intramolecular charge
transfer and to control intramolecular motions in aggregated states.
However, such conjugated D-A systems have strong dipolar moments and
intermolecular interactions, which may inhibit other channels of photothermal
conversion and are often susceptible to nucleophiles, especially in
the presence of light irradiation. Now, we report a molecular guideline
to develop novel NIR organic photothermal nanoagents based on conjugated
boron dipyrromethene (BODIPY) oligomers. This oligomerization is helpful
not only for their tunable NIR absorptions in the ground state with
distinctly redshifted absorption maxima up to 1002 nm and high extinction
coefficients but also for their highly efficient photothermal conversion
because of the possible motion of the BODIPY motifs around the ethene
linked group in the excited state. These oligomers were fabricated
as ultra-photostable nanoagents for multiple imaging-guided phototherapies,
which efficiently accumulated in tumors, and gave complete tumor ablation
with NIR laser irradiation. This strategy of “ground-state
conjugation, excited-state rotation” provides a novel guideline
to develop advanced theranostic molecules with NIR absorption.