Modulating charge transfer in cyano-functionalized covalent organic frameworks for amplified electrochemiluminescence...

Covalent organic frameworks (COFs) have gained significant attention as promising electrochemiluminescence (ECL) emitters. In this work, we synthesized a series of COFs with tunable numbers of cyano (CN) groups using a facile hydrothermal method. This structural design leverages the CN groups to construct periodic donor-acceptor (D-A) architectures, which effectively regulate the charge transfer channels and subsequently enhance the ECL efficiency. 2CN-COF (containing two β-ketoenamine rings and two CN groups) exhibits the narrowest energy gap and the shortest exciton lifetime, resulting in 9.53- or 33.37-fold ECL enhancement compared to 1CN-COF (containing two β-ketoenamine rings plus one cyano group) or 0CN-COF (containing only two β-ketoenamine rings). Density functional theory (DFT) calculations confirm that the cyano groups in 2CN-COF enhance the electron-withdrawing effect and enable a large dipole moment. This functional group engineering in framework increases the channels for charge transfer, which strengthens the donor-acceptor (D-A) effect and thereby enhances the ECL performance. The optimized 2CN-COF was subsequently employed as an efficient ECL sensor for uranyl (UO₂²⁺) detection. The sensing mechanism involves specific coordination between UO₂²⁺ and CN-derived binding sites on the COF, which disrupts the charge transfer channels and leads to significant ECL quenching. This sensor demonstrates outstanding sensitivity and high selectivity, achieving a low detection limit of 0.9 nM. This sensor not only demonstrates a rational design strategy for boosting ECL through microenvironment engineering in COFs, but also provides a reliable sensing platform for monitoring UO₂²⁺ in environmental systems, addressing the urgent need for sensitive and selective detection of radioactive contaminants.