Conformational Engineering of Two-Coordinate Gold(I) Complexes: Regulation of Excited-State Dynamics for Efficient Delayed Fluorescence

Jian-Gong Yang; Xiu-Fang Song; Gang Cheng; Siping Wu; Xingyu Feng; Ganglong Cui; Wai-Pong To; Xiaoyong Chang; Yong Chen; Chi-Ming Che; Chuluo Yang; Kai Li

doi:10.1021/acsami.2c01776

Conformational Engineering of Two-Coordinate Gold(I) Complexes: Regulation of Excited-State Dynamics for Efficient Delayed Fluorescence

ACS Appl Mater Interfaces. 2022 Mar 23;14(11):13539-13549. doi: 10.1021/acsami.2c01776. Epub 2022 Mar 14.

Authors

Jian-Gong Yang^{1

2

3}, Xiu-Fang Song⁴, Gang Cheng⁵, Siping Wu⁵, Xingyu Feng¹, Ganglong Cui⁴, Wai-Pong To⁵, Xiaoyong Chang⁶, Yong Chen³, Chi-Ming Che⁵, Chuluo Yang¹, Kai Li¹

Affiliations

¹ College of Materials Science and Engineering, Shenzhen University, Shenzhen 518055, People's Republic of China.
² College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, People's Republic of China.
³ Key Laboratory of Photochemical Conversion and Optoelectronic Materials & CAS-HKU Joint Laboratory on New Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
⁴ Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, Chemistry College, Beijing Normal University, Beijing 100875, People's Republic of China.
⁵ State Key Laboratory of Synthetic Chemistry, HKU-CAS Joint Laboratory on New Materials, and Department of Chemistry, The University of Hong Kong Pokfulam Road, Hong Kong 123, People's Republic of China.
⁶ Department of Chemistry, Southern University of Science and Technology, Shenzhen 518055, People's Republic of China.

PMID: 35286066
DOI: 10.1021/acsami.2c01776

Abstract

Carbene-Au-amide (CMA) type complexes, in which the amide and carbene ligands act as an electron donor (D) and acceptor (A), respectively, can exhibit strong delayed fluorescence (DF) from a ligand to ligand charge transfer (LLCT) excited state. Although the coplanar donor-acceptor (D-A) conformation has been suggested to be a crucial factor favoring radiative decay of the charge-transfer excited state, the geometric structural factor underpinning the excited-state mechanism of CMA complexes remains an open question. We herein develop a new class of carbene-Au-carbazolate complexes by introducing large aromatic substituents onto the carbazolate ligand, the presence of which are conceived to restrict the rotation of the Au-N bond and thus confine a twisted D-A conformation in both ground and excited states. A highly twisted D-A orientation is found for the complexes in their crystal structures. Photophysical studies reveal that the twisted conformation induces a decrease in the gap (ΔE_ST) between the lowest singlet excited state (S₁) and the triplet manifold (T₁) and thus a faster reverse intersystem crossing (RISC) from T₁ to S₁ at the expense of oscillator strength for an S₁ radiative transition. In comparison with the coplanar analogue, the twisted complexes exhibit comparable or improved DF with quantum yields of up to 94% and short emission lifetimes down to sub-microseconds. The tuning of excited-state dynamics has been well interpreted by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, which unveil much faster RISC rates for twisted complexes. Solution-processed organic light-emitting diodes (OLEDs) based on the new CMA complexes show promising performances with almost negligible efficiency rolloff at a brightness of 1000 cd m^-2. This work implies that neither a coplanar ground-state D-A conformation nor a dynamic rotation of the M-N bond is the key to the realization of efficient DF for CMA complexes.

Keywords: OLED; charge-transfer excited state; gold(I) complex; metal TADF; noncovalent interactions.