Suppression\nof Nonradiative Decay in TADF Emitters\nvia a Macrocyclic Strategy: An Experimental Study

To experimentally investigate the impact of macrocyclic\nstructures\non the nonradiative decay rate constants (<i>k</i><sub>nr</sub><sup>s</sup>) of thermally\nactivated delayed fluorescence (TADF), a macrocyclic molecule L-ring\nand its analogue NL-ring were designed and synthesized. The photophysical\nmeasurements reveal their TADF characteristics, and the <i>k</i><sub>nr</sub><sup>s</sup> of the\nL-ring (4.19 × 10<sup>6</sup> s<sup>–1</sup>) is slower\nthan that of the NL-ring (1.96 × 10<sup>7</sup> s<sup>–1</sup>), endowing the L-ring with a photoluminescence quantum yield of\n92.00%. Therefore, the L-ring device exhibited a high external quantum\nefficiency of 25.61%.