Conformational Modulation of Efficient Macrocyclic Emitters Featuring Delayed Fluorescence by Conjugation Length and Cavity Dimensions

Abstract The π‐conjugated macrocyclic emitters with thermally activated delayed fluorescence (TADF) characteristics have attracted widespread attention in the field of organic electroluminescence (EL) materials due to their unique geometries and excellent luminescence performance. Despite the significant impact of conjugation length and cavity dimensions on molecular conformation, the influence of these factors on the excited‐state properties remains understudied. Herein, we formulated a strategy aimed at modulating the conformation of TADF macrocyclic molecules containing aniline as the donor (D) unit, and triazine as the acceptor (A), linked in D−A and D‐π‐A alternative macrocyclic construction ( MC‐TNT and MC‐TST ). Corroborated by experimental and theoretical analyses, the compact and conformationally twisted MC‐TNT exhibits efficient blue luminescence in crystalline state, facilitating EL at high doping concentrations with maximum external quantum efficiency (EQE max ) of 13.9 %, leading the field of blue macrocyclic emitters. Notably, MC‐TST with π‐bridge and flat conformation, demonstrates diminished Coulombic repulsion, achieving nearly 100 % photoluminescence quantum yield and superior horizontal dipole orientation of 85 % in 5 wt % doped films, and the corresponding device‘s EQE max reaches record‐high 32.7 % within the TADF macrocyclic domain.