image: Charge separation state of PBI–4Cz are exclusively formed when photoexcited at different wavelengths. Energy dissipation of the resulting charge-separated state is subjected to the toggle between charge recombination toward ground states (Path I) and intersystem-crossing toward excited triplet states (Path II). view more
Credit: ©Science China Press
Integrating multiple photosensitive properties into an “all-in-one” photosensitizer (PS) shows great promise for the treatment of cancers owing to synergistic effect among them. However, the development of such PSs, especially those where a single laser source is needed, remains a challenge.
Yu Fang et al. report an orchestration of electron donor and acceptor in a propeller-like pentad, PBI-4Cz, where four carbazole (Cz) units are covalently linked at the ortho-positions of the perylene bisimide (PBI) core. Strong intramolecular donor-acceptor interaction significantly quenches the luminescence and largely extends the absorption spectrum to near-infrared region.
Excited state dynamics investigated via femto- and nanosecond transient absorption spectroscopy revealed exclusive charge separation of PBI-4Cz within initial 0.5 ps when photoexcited regardless of which intermediate is involved. Energy dissipation of the resulting charge separated state is subjected to toggle between intersystem crossing toward excited triplet state and charge recombination to ground state. Relative importance of the two paths can be tuned by microenvironmental polarity, which endows PBI-4Cz remarkable performance of singlet oxygen generation (>90.0%) in toluene and photothermal conversion (~28.6%) in DMSO.
The work not only show the promise for multifunctional photo-theranostics, but also provide a prototype for designing high-performance PSs with tunable photoconversion pathways through harnessing the intrinsic photostability and excited state processes of a heavy-atom-free PBI derivative.
See the article:
Orthogonal carbazole-perylene bisimide pentad: a photoconversion-tunable photosensitizer with diversified excitation and excited-state relaxation pathways
https://doi.org/10.1007/s11426-021-1154-0
Journal
Science China Chemistry