Suppression of Nonradiative Decay in TADF Emitters via a Macrocyclic Strategy: An Experimental Study

To experimentally investigate the impact of macrocyclic structures on the nonradiative decay rate constants (k_nr^s) of thermally activated delayed fluorescence (TADF), a macrocyclic molecule L-ring and its analogue NL-ring were designed and synthesized. The photophysical measurements reveal their TADF characteristics, and the k_nr^s of the L-ring (4.19 × 10⁶ s^-1) is slower than that of the NL-ring (1.96 × 10⁷ s^-1), endowing the L-ring with a photoluminescence quantum yield of 92.00%. Therefore, the L-ring device exhibited a high external quantum efficiency of 25.61%.