Manipulating spatial alignment of donor and acceptor in host-guest MOF for TADF

Xiao-Ting Liu; Weijie Hua; Hong-Xiang Nie; Mingxing Chen; Ze Chang; Xian-He Bu

doi:10.1093/nsr/nwab222

Manipulating spatial alignment of donor and acceptor in host-guest MOF for TADF

Natl Sci Rev. 2021 Dec 7;9(8):nwab222. doi: 10.1093/nsr/nwab222. eCollection 2022 Aug.

Authors

Xiao-Ting Liu¹, Weijie Hua², Hong-Xiang Nie¹, Mingxing Chen³, Ze Chang¹, Xian-He Bu^{1

4}

Affiliations

¹ School of Materials Science and Engineering, TKL of Metal and Molecule-Based Material Chemistry, Nankai University, Tianjin 300350, China.
² MIIT Key Laboratory of Semiconductor Microstructure and Quantum Sensing, Department of Applied Physics, School of Science, Nanjing University of Science and Technology, Nanjing 210094, China.
³ Analytical Instrumentation Center, Peking University, Beijing 100871, China.
⁴ State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China.

Abstract

Thermally activated delayed fluorescence (TADF) was achieved when electron-rich triphenylene (Tpl) donors were confined to a cage-based porous metal-organic framework (MOF) host (NKU-111) composed of electron-deficient 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine (Tpt) acceptor as the ligand. The spatially separated donor and acceptor molecules in a face-to-face stacking pattern generated strong through-space charge transfer (CT) interactions with a small energy splitting between the singlet and triplet excited states (∼0.1 eV), which enabled TADF. The resulting Tpl@NKU-111 exhibited an uncommon enhanced emission intensity as the temperature increased. Extensive steady-state and time-resolved spectroscopic measurements and first-principles simulations revealed the chemical and electronic structure of this compound in both the ground and low-lying excited states. A double-channel (T₁, T₂) intersystem crossing mechanism with S₁ was found and explained as single-directional CT from the degenerate HOMO-1/HOMO of the guest donor to the LUMO+1 of one of the nearest acceptors. The rigid skeleton of the compound and effective through-space CT enhanced the photoluminescence quantum yield (PLQY). A maximum PLQY of 57.36% was achieved by optimizing the Tpl loading ratio in the host framework. These results indicate the potential of the MOFs for the targeted construction and optimization of TADF materials.

Keywords: donor–acceptor; host–guest MOF; thermally activated delayed fluorescence (TADF); through-space charge transfer.