The Photophysics of Naphthalimide-Phenoselenazine Electron Donor-Acceptor Dyads: Revisiting the Heavy-Atom Effect in Thermally Activated Delayed Fluorescence

Year: 2024

Authors: Pei Y.Y., Sukhanov .AA., Chen X., Iagatti A., Doria S., Dong X., Zhao J.Z., Li Y.Q., Chi W.J., Voronkova V.K., Di Donato M., Dick B.

Autors Affiliation: Dalian Univ Technol, Frontier Sci Ctr Smart Mat, Sch Chem Engn, State Key Lab Fine Chem, 2 Ling Gong Rd, Dalian 116024, Peoples R China; Dalian Univ Technol, Sch Chem Engn, Dalian 116024, Peoples R China; Russian Acad Sci, Zavoisky Phys Tech Inst, FRC Kazan Sci Ctr, Sibirsky Tract 10 7, Kazan 420029, Russia; LENS, European Lab Nonlinear Spect, via Nello Carrara n Firenze,1, I-50019 Sesto Fiorentino, Florence, Italy; INO CNR Ist Nazl Ott, Largo Enr Fermi 6, I-50125 Florence, FI, Italy; ICCOM CNR, Via Madonna Piano 10, I-50019 Sesto Fiorentino, Fi, Italy; Ningbo Sunny Automot Optech Co LTD, 27-29 Shunke Rd, Ning 315400, Yuyao, Peoples R China; Hainan Univ, Sch Chem & Chem Engn, 58 Renmin Ave, Haikou 570228, Peoples R China; Univ Regensburg, Inst Phys & Theoret Chem, Lehrstuhl Phys Chem, D-93053 Regensburg, Germany.

Abstract: We prepared thermally activated delayed fluorescence (TADF) emitter dyads, NI-PTZ, NI-PTZ-2Br and NI-PSeZ, with naphthalimide (NI) as electron acceptor and 10H-phenothiazine (PTZ) or 10H-phenoselenazine (PSeZ) as electron donor to study the heavy-atom effect on the intersystem crossing (ISC) and reverse ISC (rISC) in the TADF emitters. The delayed fluorescence lifetimes of the dyads containing heavy atoms ((Formula presented.) =5.9 μs for NI-PSeZ and (Formula presented.) =16.5 μs for NI-PTZ-2Br, respectively) are longer than the heavy atom-free counterpart NI-PTZ ((Formula presented.) =2.0 μs). Nanosecond transient absorption (ns-TA) spectral study and the time-resolved electron paramagnetic resonance (TREPR) spectra show the presence of both 3LE and 3CS states. These findings represent solid experimental evidences for the spin-vibronic coupling mechanism of TADF. Moreover, the ns-TA spectra show that the heavy atoms don´t have a significant effect since the lifetime of the triplet transient species (1.3 μs for NI-PTZ) is not shortened in their presence (4.5 μs for NI-PSeZ and 5.3 μs for NI-PTZ-2Br). These results show that the previously claimed heavy-atom effect on rISC and TADF is not a universal principle. The femtosecond transient absorption (fs-TA) spectra of the compounds indicate the occurrence of fast charge separation within 1–2 ps, and the charge recombination is slow (>4 ns).

Journal/Review: CHEMISTRY-A EUROPEAN JOURNAL

More Information: J. Z. thanks the NSFC (22473021 and U2001222), the National Key Research and Development Program of China (No. 2023YFE0197600), the Research and Innovation Team Project of Dalian University of Technology (DUT2022TB10), the Fundamental Research Funds for the Central Universities (DUT22LAB610) and the State Key Laboratory of Fine Chemicals of Dalian University of Technology for financial support. A. A. S. and V. K. V. acknowledge financial support from the government assignment for FRC Kazan Scientific Center of RAS. M.D.D. thanks the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 871124, Laserlab, Europe, for the support.
KeyWords: heavy-atom effect; intersystem crossing; reverse intersystem crossing; thermally activated delayed fluorescence; time resolved electron paramagnetic resonance
DOI: 10.1002/chem.202403542