Molecular Planar Rigidity Promoted Aggregation-Induced Delayed Electrochemiluminescence of Organic Dots for Nucleic Acid Assay.

Developing organic aggregation-induced delayed electrochemiluminescence (AIDECL) active emitters is attractive due to their full utilization of excited species. However, current molecular designs primarily focus on the electron-deficient core benzophenone, resulting in relatively low ECL efficiency due to its flexible skeleton. Herein, we design a rigid electron acceptor, i.e., xanthenone, by inserting an oxygen bridge into the benzophenone moiety, and an AIDECL-active organic dot (OD) composed of a xanthenone-dimethylacridine compound is constructed. High ECL efficiency is achieved for the resultant ODs, with a 3-fold enhancement compared to control ODs. Oxygen bridge-induced planar moiety rigidifies the molecular configuration, further inhibiting intramolecular motions and thus suppressing nonradiative decay, supported by the single-crystal data together with theoretical calculations. Significantly, an ECL biosensor is constructed employing these ODs as emitters for the sensitive analysis of miR-21 associated with pancreatic cancer, which demonstrates a low detection limit of 2.8 fM. Our investigation provides a promising way to design efficient ECL emitters and deepens the understanding of structure-property relationships.