Long-Lived Triplet Charge Separated State and Thermally Activated Delayed Fluorescence in a Compact Orthogonal Anthraquinone-Phenothiazine Electron Donor-Acceptor Dyad

Xiaoyu Zhao; Andrey A Sukhanov; Xiao Jiang; Jianzhang Zhao; Violeta K Voronkova

doi:10.1021/acs.jpclett.2c00435

Long-Lived Triplet Charge Separated State and Thermally Activated Delayed Fluorescence in a Compact Orthogonal Anthraquinone-Phenothiazine Electron Donor-Acceptor Dyad

J Phys Chem Lett. 2022 Mar 24;13(11):2533-2539. doi: 10.1021/acs.jpclett.2c00435. Epub 2022 Mar 14.

Authors

Xiaoyu Zhao^{1

2}, Andrey A Sukhanov³, Xiao Jiang⁴, Jianzhang Zhao^{1

2}, Violeta K Voronkova³

Affiliations

¹ State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, P. R. China.
² State Key Laboratory of Chemistry and Utilization of Carbon Based Energy Resources, College of Chemistry, Xinjiang University, Urumqi 830017, P. R. China.
³ Zavoisky Physical-Technical Institute, FRC Kazan Scientific Center of Russian Academy of Sciences, Kazan 420029, Russia.
⁴ Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, P. R. China.

PMID: 35285632
DOI: 10.1021/acs.jpclett.2c00435

Abstract

A long-lived triplet charge separated state (³CS state lifetime: 0.56 μs) was observed in a compact electron donor-acceptor dyad with electron donor phenothiazine (PTZ) and acceptor anthraquinone (AQ) directly connected by a single C-N bond (AQ-PTZ). The ¹CS state energy (2.0 eV in cyclohexane) is lower than those of the ³AQ (2.7 eV) or the ³PTZ state (2.6 eV). By oxidation of the PTZ unit, thus increasing of the ¹CS state energy (2.7 eV in cyclohexane), thermally activated delayed fluorescence (TADF) was observed [τ = 17.7 ns (99.9%)/1.5 μs (0.1%)]. Time-resolved electron paramagnetic resonance (TREPR) spectra confirm the electron spin multiplicity of the ³CS state, and the zero-field-splitting (ZFS) parameters |D| and |E| are 48.2 mT and 11.2 mT, respectively. These results are useful for design of compact electron donor-acceptor dyads to access the long-lived ³CS state and study the TADF mechanism.