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

Abstract 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.