A Furan Prism Cage: Synthesis, Guest Recognition, and Applications in Constructing Charge-Transfer Co-crystals

Abstract

Supramolecular hosts featuring well-defined cavities and electron-rich architectures are highly attractive for functional applications, yet their synthesis-particularly for three-dimensional organic cages-often relies on complex, irreversible reaction pathways. Herein, we report the synthesis of an electron-rich furan prism cage (FPC) bearing π-conjugated platforms and pillars, which displays strong host-guest affinities toward a broad range of guests, including both electrondeficient and electron-rich species. Single-crystal and solid-state studies reveal two distinct binding modes, corresponding to host-guest stoichiometries of 1:2 and 1:1. In the 1:2 complexes, one guest is encapsulated within the cavity while the second associates with the exo-wall of the cage, enabling the formation of ordered supramolecular networks through cooperative intra-and intermolecular π•••π interactions. In contrast, the 1:1 binding mode leads to less ordered solid-state arrangements. Notably, complexation with electron-deficient guests, including 1,2,4,5-tetracyanobenzene (TCNB) and tetrafluoroterephthalonitrile (TFTN), gives rise to pronounced charge-transfer interactions, which are manifested by distinct color changes, bathochromic shifts in solid-state absorption, and altered luminescence behaviors. One of these cage-guest complexes in the solid state demonstrates vapochromic behavior, whose color undergoes visible switching upon exposure to pyridine derivatives. These results demonstrate that precise control over host-guest stoichiometry and solid-state organization enables effective modulation of charge-transfer states, highlighting the potential of electron-rich threedimensional cages as versatile platforms for charge-transfer-based optical materials.