# Interlocked Rotaxane Enables TADF with Distinct Excited-State Structural Relaxation

## TL;DR

This paper introduces a new type of TADF exciplex based on an interlocked rotaxane structure, which improves the efficiency and stability of OLEDs.

## Contribution

The first rotaxane-based TADF exciplex with distinct excited-state structural relaxation is demonstrated.

## Key findings

- The CT-Rotaxane exhibits a small singlet–triplet energy gap and fast reverse intersystem crossing.
- The rotaxane TADF exciplex shows structural relaxation in both solution and solid state.
- Rotaxane-type OLEDs achieved a peak external quantum efficiency of 7.23% with improved operational stability.

## Abstract

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.