Red Thermally Activated Delayed Fluorescence and the Intersystem Crossing Mechanisms in Compact Naphthalimide-Phenothiazine Electron Donor/Acceptor Dyads

Year: 2019

Authors: Tang GL., Sukhanov AA., Zhao JZ., Yang WB., Wang ZJ., Liu QY., Voronkova VK., Di Donato M., Escudero D., Jacquemin D.

Autors Affiliation: Dalian Univ Technol, Sch Chem Engn, State Key Lab Fine Chem, Dalian 116024, Peoples R China; RAS, Zavoisky Phys Tech Inst, FRC Kazan Sci Ctr, Kazan 420029, Russia; Xinjiang Univ, Sch Chem & Chem Engn, Minist Educ, Inst Appl Chem, Urumqi 830046, Peoples R China; Xinjiang Univ, Key Lab Energy Mat Chem, Minist Educ, Inst Appl Chem, Urumqi 830046, Peoples R China; Shandong Univ Sci & Technol, Coll Chem & Environm Engn, Qingdao 266590, Shandong, Peoples R China; European Labor Nonlinear Spect, Via N Carrara 1, I-50019 Sesto Fiorentino, Italy; Ist Nazl Ott Largo Enrico, INO, Fermi 6, I-50125 Florence, Italy; Katholieke Univ Leuven, Dept Chem, Celestijnenlaan 200F, B-3001 Leuven, Belgium; Univ Nantes, Lab CEISAM, CNRS, UMR 6230, 2 Rue Houssiniere, F-44322 Nantes 3, France

Abstract: Controlling the electronic coupling between electron donor and acceptor subunits in a dyad is pivotal for the development of novel organic materials, for instance, thermally activated delayed fluorescence (TADF) materials and triplet photosensitizers. Herein, we prepared two compact electron donor/acceptor dyads based on phenothiazine (PTZ) and naphthalimide (NI) with different conformation restrictions induced by the C-N (NI-N-PTZ) or C-C (NI-C-PTZ) linkers. The effect of electronic coupling (matrix elements, V-DA) on the photophysical properties, especially the intersystem crossing (ISC) and the TADF, were investigated. NI-C-PTZ shows stronger ground-state electronic coupling (V-DA = 2548 cm(-1)) compared to NI-N-PTZ (V-DA = 870 cm(-1)). TADF was observed only for NI-N-PTZ due to its smaller electronic coupling. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy indicated the presence two triplet excited states and three ISC mechanisms in NI-N-PTZ with different electron spin polarizations (ESP): radical pair ISC (RP-ISC) and spin-orbital charge transfer ISC (SOCT-ISC) for one triplet state, and spin-orbital coupling ISC (SO-ISC) for another. Moreover, for the second one, an inversion of the electron spin polarization (ESP) was observed at 0.5-1.1 mu s delay time. NI-N-PTZ represents a rare example for compact electron donor/acceptor dyad showing TADF emission in the red spectral region.


Volume: 123 (50)      Pages from: 30171  to: 30186

More Information: J.Z. thanks the NSFC (21673031, 21761142005, and 21911530095), the State Key Laboratory of Fine Chemicals (ZYTS201901), and the Fundamental Research Funds for the Central Universities (DUT2019TA06) for the financial support. A.A.S. and V.K.V. acknowledge the financial support from the Government of the Russian Federation (Mega-grant No. 14.W03.31.0028) and the Russian Foundation for Basic Research (Project 19-53-53013). D.E. thanks funding from Internal Funds KU Leuven. This work used the computational resources of the CCIPL computing center installed in Nantes, France.
DOI: 10.1021/acs.jpcc.9b09335

Citations: 58
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