Pressure-driven steric hindrance engineering for maximizing photoluminescence in covalent organic frameworks

Covalent organic frameworks (COFs) are promising platforms for smart photoluminescent (PL) materials, but their emission is often quenched by π-π stacking-induced nonradiative transitions. Here, we use a pressure-treatment strategy on a series of sterically engineered pyrene-based imine COFs-Py-Da-COF, Py-Da-2CH₃-COF, and Py-Da-4CH₃-COF-to achieve steric-hindrance-responsive PL enhancement. Notably, the pressure-treated Py-Da-4CH₃-COF exhibits an increase in PL quantum yield, reaching a record-high value of 91.5% from the initial 14.7%. Experimental and theoretical analyses reveal that the bulky methyl substituents elevate the phase transition barrier, locking the COF into an irreversible a quasi-AB stacking configuration. This structural rearrangement suppresses π-π interactions and restricts carbon-hydrogen vibrations, minimizing nonradiative decay. Our work establishes a generalizable approach to designing high-performance PL COFs for practical optoelectronic applications.