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Electronic Coupling and Spin–Orbit Charge-Transfer Intersystem Crossing in Phenothiazine–Perylene Compact Electron Donor/Acceptor Dyads

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journal contribution
posted on 2019-03-01, 00:00 authored by Muhammad Imran, Andrey A. Sukhanov, Zhijia Wang, Ahmet Karatay, Jianzhang Zhao, Zafar Mahmood, Ayhan Elmali, Violeta K. Voronkova, Mustafa Hayvali, Yong Heng Xing, Stefan Weber
We prepared perylene (Pery)-phenothiazine (PTZ) compact donor/acceptor dyads with connection at either N- or 2-C positions of the PTZ moiety to attain molecular conformation restriction and to study the relationship between mutual chromophore orientation and spin–orbit charge-transfer intersystem crossing (SOCT-ISC) efficiency. In Pery-N-PTZ, the linkage is at the N-position of the PTZ moiety, and the molecule adopts an orthogonal geometry (φ = 91.5°), whereas in Pery-C-PTZ, the connection is at the 2-C position, resulting in a more planar geometry (φ = 60.6°). A diphenylamino derivative (Pery-DPA) was also prepared in which a N atom is fully π-conjugated with the perylene moiety. Highly solvent polarity-dependent singlet oxygen production was observed for the dyads (ΦΔ = 3–60%), which is an indication of the SOCT-ISC mechanism. The potential energy curve of the torsion about the C–N/C–C linker indicated different energy landscapes for the dyads; interestingly, we found that nonorthogonal geometry also induces efficient SOCT-ISC, which is different from previous studies. The ultrafast charge separation process (<100 fs) and the ISC rate (0.27 ps) were observed by femtosecond transient absorption spectroscopy. Time-resolved electron paramagnetic resonance spectroscopy further confirmed the SOCT-ISC mechanism. With perylenebisimide as the triplet acceptor and the dyads as the triplet photosensitizer, the triplet–triplet annihilation-induced delayed fluorescence was observed, with the luminescence lifetime up to 71 μs.

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