Aggregation-induced delayed electrochemiluminescence of organic dots in aqueous media

Full utilization of the excited species at both singlet states (R-1*) and triplet states (R-3*) is crucial to improving electrochemiluminescence (ECL) efficiency but is challenging for organic luminescent materials. Here, an aggregation-induced delayed ECL (AIDECL) active organic dot (OD) containing a benzophenone acceptor and dimethylacridine donor is reported, which shows high ECL efficiency via reverse intersystem crossing (RISC) of non-emissive R-3* to emissive R-1*, overcoming the spin-forbidden radiative decay from R-3*. By introducing dual donor-acceptor pairs into luminophores, it is found that nonradiative pathway could be further suppressed via enhanced intermolecular weak interactions, and multiple spin-up conversion channels could be activated. As a consequence, the obtained OD enjoys a 6.8-fold higher ECL efficiency relative to the control AIDECL-active OD. Single-crystal studies and theoretical calculations reveal that the enhanced AIDECL behaviors come from the acceleration of both radiative transition and RISC. This work represents a major step towards purely organic, high-efficiency ECL dyes and a direction for the design of next-generation ECL dyes at the molecular level.