Design and Synthesis of Box[6]arenes for 3D Charge‐Transfer Co‐Crystal Engineering via Macrocyclic Self‐Complementary and Exo‐Wall Interactions

The construction of well-defined 3D charge-transfer (CT) co-crystals using new macrocyclic hosts to enable programmable functionality remains challenging due to the dimensional constraints imposed by conventional assembly strategies. Herein, we address this limitation using a new synthetic macrocycle named box[6]arene (B[6]A) with a flexible skeleton, which adopts two distinct conformations (B[6]Aα and B[6]Aβ). Crucially, the self-complementary and exo-wall CT co-assembly of B[6]A facilitates the construction of 3D macrocycle-based co-crystals (MCCs) with planar electron-deficient guests, including 1,2,4,5-tetracyanobenzene (TCNB), tetrafluoroterephthalonitrile (TFTN), and tetrachloroterephthalonitrile (TClTN). These MCCs exhibit tunable fluorescence with emission maxima at 690, 594, and 592 nm, respectively. Notably, activated B[6]A-TCNB demonstrates selective vapochromic behaviors toward picoline isomers via a dual response mechanism. This study provides new insights into the design of functional macrocyclic arenes and 3D MCCs, paving the way for the development of color-tunable crystalline luminescent materials and advanced vapochromic systems.