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.