Interlocked Rotaxane Enables TADF with Distinct Excited-State Structural Relaxation

We present the first demonstration of a rotaxane-based thermally activated delayed fluorescence (TADF) exciplex, its unique excited-state structural relaxation and application in organic light-emitting diodes (OLEDs). 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 quenched 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 (τ ≈ 264 ps) and solid state (τ ≈ 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 nonrotaxane 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.