Beyond Planar Architectures: Oxacalix[4]Arene ‐Bridged 3D Covalent Organic Frameworks with Saddle‐Shaped π‐Cavities for Efficient Hydrogen Peroxide Photogeneration and Non‐Covalent C60 Confinement

Abstract In this work, two calixarene‐based macrocyclic 3D COFs (XJU‐3, XJU‐4) are successfully developed by overcoming conformational instability via intramolecular heteroatom anchoring and peripheral structural extension. The stabilized saddle‐shaped conformation endows XJU‐4 with exceptional crystallinity and directional charge transfer channels, achieving an efficient hydrogen peroxide (H 2 O 2 ) production rate of 8384 µmol g 1 h −1 under pure water and oxygen (O 2 ) conditions, which further rises to 24605 µmol g 1 h −1 with a sacrificial agent. Combined experimental and theoretical analyses reveal that the curved π‐cavity facilitates O 2 activation through enhanced electron‐withdrawing effects, while the orthogonal dimer configuration promotes singlet oxygen ( 1 O 2 ) intermediates via reduced singlet‐triplet energy gaps (ΔE S‐T ). Building on this framework, the potential of calixarene cavities is further demonstrated as supramolecular hosts—C 60 is selectively encapsulated within their π‐rich pockets through non‐covalent interactions, distinct from conventional pore confinement or covalent linkage strategies. This host‐guest synergy enhances charge transfer pathways, as evidenced by luminescence quenching and orbital localization, showcasing the versatility of these COFs in both catalysis and functional composite design. The work establishes a paradigm for engineering conformation‐stable macrocycles into 3D COFs, expanding their functional design for solar energy conversion systems.