Intermolecular Interactions Override Chemical Intuition in Tuning Stacking and Electronic Properties of Functionalized Two-Dimensional Covalent Organic Frameworks

Rising energy demands underscore the need for renewable energy solutions such as solar energy. Covalent organic frameworks (COFs), with their tunable compositions, structures, and photophysical properties, are promising candidates; however, a comprehensive understanding of their composition-structure–property relationships remains limited. Here, combining all-electron quantum chemistry with coarse-grained Holstein Hamiltonians, we show that although slipped-stacked configurations are generally most stable, the degree of slipping is strongly influenced by the nature of the functional groups and does not follow simple electron-donating or -withdrawing trends. While van der Waals interactions primarily drive the stacking behavior, electrostatic contributions unique to each substituent modulate its extent. Furthermore, we find that in highly symmetric lattice backbones, small substituent changes have minimal effect on electronic structure, whereas symmetry-breaking functionalization offers a robust and effective route to tune electronic, transport, and photophysical properties. While the stacking arrangement primarily governs interlayer electron coherence, its influence diminishes in the high-disorder regime. Our findings provide fundamental insights and design principles to guide the development of high-performance COFs for photocatalytic applications.