Achieving quantum confinement effect in covalent organic frameworks for high photoluminescence

Summary

Although the quantum confinement effect has been achieved through physical size reduction, it has never been realized via exciton radius modulation without physical downsizing. Here, by introducing "breakpoints" of conjugation into the covalent organic frameworks (COFs), it is found that the engineered π-conjugated domains could enable the intrinsic exciton confinement at the molecular level, bypassing the need for physical downsizing unprecedentedly. This strategy remarkably bears the quantum confinement effect in the trans-1,4-diaminocyclohexane (tDACH)-COF, enabling a photoluminescence quantum yield (PLQY) of 73%, making it incomparable to all existing COFs. Furthermore, we demonstrated that the protonation in the tDACH-COF could expand the exciton radius within the framework using transient spectroscopy. Consequently, the tDACH-COF exploited in this work exhibited exceptional nerve agent sensing performance with an extremely low detection limit of 4.6 ppb and superior selectivity. This work represents a revolutionary breakthrough in both quantum physics and crystalline organic porous materials and will redefine quantum engineering principles.