Orthogonal carbazole-perylene bisimide pentad: a photoconversion-tunable photosensitizer with diversified excitation and excited-state relaxation pathways

• Published in: Science China. Chemistry 2021-12, Vol.64 (12), p.2193-2202
• Main Authors: Wang, Zhaolong, Sun, Yue, Lin, Simin, Wang, Gang, Chang, Xingmao, Gou, Xinyu, Liu, Taihong, Jin, Shengye, He, Gang, Wei, Yu-Chen, Chou, Pi-Tai, Fang, Yu
• Format: Article
• Language: English
• Subjects: Absorption spectra; Absorption spectroscopy; Carbazoles; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Energy dissipation; Excitation; Infrared spectra; Near infrared radiation; Photosensitivity; Photothermal conversion; Spectrum analysis; Synergistic effect; Toluene
• ISSN: 1674-7291; 1869-1870
• DOI: 10.1007/s11426-021-1154-0

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 that need a single laser source, remains a challenge. Herein, we report an orchestration of electron donors and acceptors in a propeller-like pentad, PBI - 4Cz , where four carbazole (Cz) units are covalently linked to the ortho-positions of the perylene bisimide (PBI) core. Strong intramolecular donor-acceptor interaction significantly quenches the luminescence and largely extends the absorption spectra to near-infrared region. Excited-state dynamics investigated via femto- and nano-second transient absorption spectroscopy revealed exclusive charge separation of the PBI - 4Cz within initial 0.5 ps when photoexcited regardless of which intermediate is involved. Energy dissipation of the resulting charge-separated state (PBI •− -4Cz •− ) is subjected to the toggle between intersystem-crossing toward excited triplet states and charge recombination toward ground states. Relative importance of the two pathways can be tuned by micro-environmental polarity, which endows PBI - 4Cz remarkable performances of singlet-oxygen generation (>90.0%) in toluene and photothermal conversion (∼28.6%) in DMSO. Harnessing intrinsic photostability and excited-state processes of heavy-atom-free PBI derivatives not only holds a promise for multifunctional phototheranostics, but also provides a prototype for designing high-performance PSs with tunable photoconversion pathways.