We
report that conjugated polymer nanoparticles (CPNs) coated with
polyethylene glycols (PEGs) exhibit photothermal and photodynamic
capabilities according to molecular ordering in their assembly structures.
CPN-PEGs were made using three different methods: a dispersion process
of phase-separated film assemblies of a conjugated polymer and a phospholipid-conjugated
PEG (CPN-I), a dispersion process of a conjugated polymer and a phospholipid
followed by surface conjugation with PEGs (CPN-II), and a miniemulsification
of the conjugated polymer and the phospholipid-conjugated PEG. Our
findings revealed that the ordered molecular assembly structures in
CPN-I and CPN-II increased intermolecular interactions and decreased
the optical band gap, promoting nonradiative exciton relaxation via
the energy-gap law’s internal conversion mechanism and rationalizing
CPN-I’s shorter singlet exciton lifetime (13 ps). Meanwhile,
CPN-III with a disordered structure generated more singlet oxygen
than CPN-I and CPN-II, indicating increased triplet exciton generation
upon the polaron recombination. Our findings present that the photothermal
and photodynamic properties of CPNs are obviously dependent on the
assembly structure order and that CPNs with an ordered assembly of
conjugated backbones have a stronger photothermal effect, whereas
those with a disordered structure have a better photodynamic effect.
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