Intersystem Crossing and Triplet-State Property of Anthryl- and Carbazole-[1,12]fused Perylenebisimide Derivatives with a Twisted π‑Conjugation Framework
Heavy atom-free triplet photosensitizers (PSs) are particularly of interest concerning both fundamental photochemistry study and practical applications. However, achieving efficient intersystem crossing (ISC) in planar heavy atom-free aromatic organic compounds is challenging. Herein, we demonstrate...
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Published in: | The journal of physical chemistry. B 2021-08, Vol.125 (32), p.9317-9332 |
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Main Authors: | , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
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Online Access: | Get full text |
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Summary: | Heavy atom-free triplet photosensitizers (PSs) are particularly of interest concerning both fundamental photochemistry study and practical applications. However, achieving efficient intersystem crossing (ISC) in planar heavy atom-free aromatic organic compounds is challenging. Herein, we demonstrate that two perylenebisimide (PBI) derivatives with anthryl and carbazole moieties fused at the bay position, showing twisted π-conjugation frameworks and red-shifted UV–vis absorption as compared to the native PBI chromophore (by 75–1610 cm–1), possess efficient ISC (singlet oxygen quantum yield: ΦΔ = 85%) and a long-lived triplet excited state (τT = 382 μs in fluid solution and τT = 4.28 ms in solid polymer film). Femtosecond transient absorption revealed ultrafast intramolecular charge-transfer (ICT) process in the twisted PBI derivatives (0.9 ps), and the ISC takes 3.7 ns. Pulsed laser excited time-resolved electron paramagnetic resonance (TREPR) spectra indicate that the triplet-state wave function of the twisted PBIs is mainly confined on the PBI core, demonstrated by the zero-field-splitting D parameter. Accordingly, the twisted derivatives have higher T1 energy (E T1 = 1.48–1.56 eV) as compared to the native PBI chromophore (1.20 eV), which is an advantage for the application of the derivatives as triplet PSs. Theoretical computation of the Franck–Condon density of states, based on excited-state dynamics methods, shows that the efficient ISC in the twisted PBI derivatives is due to the increased spin–orbit coupling matrix elements for the S1–T1 and S1–T2 states [spin–orbit coupling matrix element (SOCME): 0.11–0.44 cm–1. SOCME is zero for native PBI], as well as the Herzberg–Teller vibronic coupling. For the planar benzoPBI, the moderate ISC is due to S1 → T2 transition (SOCME: 0.03 cm–1. The two states share a similar energy, ca. 2.5 eV). |
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ISSN: | 1520-6106 1520-5207 |
DOI: | 10.1021/acs.jpcb.1c05032 |