<i>N,O</i>‐Alternant Belt[3]arene Utilized for Construction of Multi‐Color Supramolecular TADF Materials and Highly Selective Detection of 2‐Cyanopyrazine

In this work, 3,6-dimethoxycalix[3]acridine (3,6-DMO-C[3]A), as a new macrocyclic arene, was synthesized and then applied to the construction of a new kind of N,O-alternant belt[3]arene (NOAB[3]A) by the conversion approach from macrocycle to belt. NOAB[3]A has a regularly hexagonal structure and electron-rich cavity, and it can be successfully utilized as an electron donor to construct supramolecular thermally activated delayed fluorescence (STADF) materials with multi-color emissions by its complexation with electron acceptors with different electron-deficient abilities. Notably, due to the formation of STADF accompanied by fluorescence enhancement and redshift when NOAB[3]A combines with the cyanide-containing aromatic compounds, the belt[3]arene can also be directly used for highly selective, sensitive, and visual detection of 2-cyanopyrazine (2-CP) vapor at trace level. The limit of detection (LOD) concentration for 2-CP reached 1.7 mg L^-1, indicating that NOAB[3]A can serve as an excellent sensing platform for detecting 2-CP. This work not only expands the applications of functionalized belt[n]arenes but also provides an innovative insight into the detection application of the STADF strategy.