Face-to-Face Orientation of Quasiplanar Donor and Acceptor Enables Highly Efficient Intramolecular Exciplex Fluorescence

Intramolecular through-space charge-transfer (TSCT) excited states have been exploited for developing thermally activated delayed fluorescence (TADF) emitters, but the tuning of excited state dynamics by conformational engineering remains sparse. Designed here is a series of TSCT emitters with precisely controlled alignment of the donor and acceptor segments. With increasing intramolecular pi-pi interactions, the radiative decay rate of the lowest singlet excited state (S-1) progressively increased together with a suppression of nonradiative decay, leading to significantly enhanced photoluminescence quantum yields of up to 0.99 in doped thin films. A high-efficiency electroluminescence device, with a maximum external quantum efficiency (EQE) of 23.96 %, was achieved and maintains >20 % at a brightness of 1000 cd m(-2). This work sheds light on the importance of conformation control for achieving high-efficiency intramolecular exciplex emitters.

Automated summary

Intramolecular through-space charge-transfer (TSCT) excited states are utilized for developing thermally activated delayed fluorescence (TADF) emitters, with a series of precisely controlled TSCT emitters designed through alignment optimization of donor and acceptor segments. By increasing intramolecular pi-pi interactions, radiative decay rate of the lowest singlet excited state (S-1) is progressively enhanced with suppression of nonradiative decay, leading to significantly improved photoluminescence quantum yields of up to 0.99 in doped thin films. A high-efficiency electroluminescence device achieves a maximum external quantum efficiency (EQE) of 23.96% and maintains >20% at a brightness of 1000 cd m(-2), highlighting the importance of conformation control for high-efficiency intramolecular exciplex emitters.