Stacking Effects on the Optoelectronic Properties of 2D Perylene-Zn-Porphyrin-Based COFs.

Crystalline porous materials, such as covalent organic frameworks (COFs), have emerged as promising candidates for photocatalytic and optoelectronic applications due to their tunable architecture and capacity to mitigate charge recombination. The incorporation of highly aromatic organic building blocks that promote self-assembly and columnar growth enables the formation of COFs with a controlled layer thickness. However, the influence of interlayer stacking on the structural and optoelectronic behaviors of these materials remains poorly understood. In this work, we combine experimental and theoretical approaches to elucidate the stacking-induced evolution of perylene-Zn-porphyrin COFs. Spectroscopic and microscopic analyses, supported by density functional theory (DFT) calculations, reveal that self-assembly through AA stacking markedly modifies both the geometry and electronic structure. The transition from nonplanar 2D architectures to planar multilayered frameworks results in reduced band gaps, inversion of the frontier crystalline orbital delocalization, and a shift of absorption dominance toward the porphyrin units. These findings demonstrate that controlled layer stacking is a viable strategy to tailor the electronic and optical properties of stacked 2D COFs, paving the way for their integration into high-performance optoelectronic devices.