Programmable Vertical Expansion of Bilayer 2D Supramolecular Frameworks via Molecular Pillar Engineering

Achieving quantitative control over interlayer spacing in multilayer two-dimensional (2D) supramolecular organic frameworks (SOFs) remains a fundamental challenge. Here, we report a molecular pillar engineering strategy enabling programmable vertical expansion of bilayer architectures. By designing elongated bipyridine pillars L2/L3 (3.0/4.4 nm) with hydrophilic side chains, we transform a Zn-porphyrin/CB[8] monolayer SOF (ml-2D-SOF, 1.8 nm) into bilayers with precision-tuned thicknesses: bl-2D-SOF-2 (5.4 ± 0.2 nm) and bl-2D-SOF-3 (6.7 ± 0.3 nm). Synchrotron small-angle and wide-angle X-ray scattering (SAXS/WAXS), transmission electron microscopy (TEM) lattice imaging, and atomic force microscopy (AFM) confirm structural regularity with Ångstrom-level accuracy in layer spacing. Crucially, we establish a linear correlation between pillar length and interlayer distance, while multivalency-driven assembly ensures >93% bilayer selectivity. This work pioneers quantitative 3D engineering in 2D SOFs, opening avenues for tailored nanoconfined environments.