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 electron-deficient 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 three-dimensional cages as versatile platforms for charge-transfer-based optical materials.