Department of Chemistry

• The full article entitled “Interlocked Rotaxane Enables TADF with Distinct Excited-State Structural Relaxation” can be found at the JACS website at https://doi.org/10.1021/jacs.5c19031
• Authors: Chuan-Jing Lin, Kai-Hsin Chang, Chun-Yen Lin, Kuan-Hsuan Su, Chieh-Ming Hung, Yi-Hung Liu, Orion Shih,* Ken-Tsung Wong,* and Pi-Tai Chou*

The research team of Prof. Pi-Tai Chou and Prof. Ken-Tsung Wong in the Department of Chemistry, National Taiwan University, presents the first demonstration of a rotaxane-based TADF exciplex, whose unique excited-state structural relaxation and application in OLEDs are reported. The design employs a triazene cage (Trz-cage) as the host electron acceptor, threaded by a carbazole derivative with ethylene glycol ether chains serving as the guest donor, and capped at both ends with bulky triphenylmethane stoppers, thus forming the rotaxane exciplex, namely the charge-transfer CT-Rotaxane. The TADF nature of CT-Rotaxane is evidenced by microsecond-scale delayed fluorescence subject to quenching by oxygen, a small singlet–triplet energy gap (ΔE_ST = 0.084 eV), and a fast reverse intersystem crossing rate of 9.8 × 10⁵ s⁻¹ in toluene. Notably, the rotaxane TADF exciplex undergoes pronounced structural relaxation in both solution (t ≈ 264 ps) and solid state (t ≈ 177 ns), corroborated by combined quantum mechanical and molecular dynamics simulations. Importantly, the interlocked CT-Rotaxane enabled the fabrication of rotaxane-type OLEDs that delivered green electro-luminescence (EL) with a peak external quantum efficiency (EQE) of 7.23% at 263 cd m^-2—surpassing the reference non-rotaxane 1@Trz-cage and TrMe@Trz-cage exciplex OLEDs in efficiency and operational stability, respectively. These findings underscore mechanically interlocked TADF exciplexes as a promising strategy for optoelectronic applications.  

Figure 1. The first demonstration of a rotaxane-based TADF exciplex, CT-Rotaxane, which undergoes pronounced structural relaxation in both solution and solid state and offers superiority in operational stability of OLEDs.