Nanoscopy

Controlling stacking architecture in covalent organic frameworks (COFs) films remains a fundamental challenge in interfacial polymerization because interlayer alignment directly governs π–π coupling and band structure. While dynamic covalent chemistry enables structural error correction, externally addressable stimuli capable of biasing stacking architecture during growth - without altering framework composition - remain scarcely explored. Here, we demonstrate that photonic activation functions as an independent process parameter that directs stacking architecture during surfactant-monolayer-assisted interfacial synthesis (SMAIS) at the air–water interface. Using a porphyrin-based COF as a model system, wavelength-selective illumination (420–640 nm) induces a reproducible hypsochromic shift of the Q-band relative to dark-grown films and increases the optical band gap by 110 meV. Spectroscopy of films collected at defined growth times reveals earlier emergence of COF-characteristic signatures under illumination. Quantum chemical calculations disentangle the electronic contributions of linker functionalization, lateral network extension, and interlayer coupling, identifying the Q-band as a sensitive probe of stacking geometry. The calculations predict a weaker bathochromic response for AB stacking compared to slipped AA′ stacking. Consistent with this prediction, transmission electron microscopy reveals a light-dependent lattice contraction from 2.50 nm to 1.76 nm, supporting the assignment of preferential AB-type stacking under illumination. Atomic force microscopy further demonstrates wavelength- and time-dependent modulation of vertical film build-up under illumination, yielding thinner multilayer films and revealing a shift in the balance between interfacial growth and structural reorganization. Together, these results establish light as a controllable stimulus for directing stacking registry and tuning interlayer electronic coupling during dynamic covalent growth at soft interfaces.