Self‐Contained Calix[3]Acridans with Macrocyclization Induced TADF Property for Highly Selective Recognition of Fe ³⁺ and Detection of Oxidation Degree of Pyrite Medicinal Herbs

In this work, a new synthetic strategy for construction of macrocyclic arenes with thermally activated delayed fluorescence (TADFMAs) property was developed. Consequently, a series of acceptor-linked calix[3]acridans (o-/m-/p-AC) with self-contained structures were synthesized by the template effect and the ''2 + 1″ fragment coupling reaction. By utilizing the macrocyclic confinement effect to establish through-space charge transfer (TSCT) pathways and realize effective donor-acceptor separation, excellent TADF properties of o-/m-/p-AC in both solution and solid state were achieved. Compared to the monomers, the macrocyclization strategy not only significantly enhanced TADF emission of TADFMAs but also enabled the emergence of TADF property from their originally non-TADF systems. Moreover, these TADFMAs also exhibited multicolor property through positional isomerization effects and tunable self-assembly. Especially, o-AC exhibited highly selective recognition toward Fe³⁺ in solution with the limit of detection (LOD) concentration of 3.8 µM, which was two orders of magnitude lower than the o-monomer. Furthermore, the detection of the oxidation degree of pyrite-based medicinal herbs was achieved. This work represents the pioneering example of TADFMAs in detection, and provides a new insight into the development of organic luminescent materials.