Abstract
We report the characterization of rotaxanes based on a carbazole‐benzophenone thermally activated delayed fluorescence luminophore. We find that the mechanical bond leads to an improvement in key photophysical properties of the emitter, notably an increase in photoluminescence quantum yield and a decrease in the energy difference between singlet and triplet states, as well as fine tuning of the emission wavelength, a feat that is difficult to achieve when using covalently bound substituents. Computational simulations, supported by X‐ray crystallography, suggest that this tuning of properties occurs due to weak interactions between the axle and the macrocycle that are enforced by the mechanical bond. This work highlights the benefits of using the mechanical bond to refine existing luminophores, providing a new avenue for emitter optimization that can ultimately increase the performance of these molecules.
Highlights
Organic compounds exhibiting thermally activated delayed fluorescence (TADF) have enjoyed tremendous recent attention due to their ability to undergo efficient spin state changes between the low-lying excited states
TADF is the result of two successive processes: reverse intersystem crossing from the lowest excited triplet (T1) to the lowest excited singlet state (S1), followed by the emission from S1 to the ground state (S0)
The design of prototypical interlocked TADF emitters [2]rotaxane 1&2 and [3]rotaxane 1&22 (Figure 1 a) was based on the carbazole-benzophenone system developed by Zysman-Colman and co-workers.[22]
Summary
Organic compounds exhibiting thermally activated delayed fluorescence (TADF) have enjoyed tremendous recent attention due to their ability to undergo efficient spin state changes between the low-lying excited states. The challenge of enhancing krISC by decreasing DEST whilst maintaining sufficient kr, to give high photoluminescence quantum yield, FPL, has motivated a significant amount of experimental[11] and computational[12] work focused on both elucidating and resolving the complex interplay between the photophysical properties of TADF materials This has demonstrated, with the exception of multi-resonance emitters,[13] the importance of the rotational freedom around the D-A bond to permit vibronic coupling between T1 and other low lying triplet excited states which aids rISC to the S1 state, combined with a near 908 mean dihedral angle between donor and acceptor to minimise DEST. We report a series of carbazole-benzophenone-based rotaxanes that demonstrate the ability of the environment provided by the macrocycles threaded close to the emitting core to fine-tune the photophysical properties of a TADF-active axle in solution and thin films.[21]
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