Significantly Improving the Electrochemiluminescence of Organic Luminophores by Regulating the Intermolecular Spacing via Flexible Alkyl Molecular Chains

Indole[3, 2-b]carbazole (ICZ) derivatives have an extended, rigid planar structure and have poor solubility in conventional organic solvents. This limited solubility restricts the mobility of molecules in the solution, promoting π -π stacking and thereby hindering the efficiency of electrochemiluminescence (ECL). In the ECL system, effective electron transfer is crucial for luminescence. Molecular aggregation will interrupt the conductive pathway, hinder charge migration, and reduce the overall performance of ECL. Here, we report a molecular engineering strategy for introducing aromatic groups and alkyl chains at the nitrogen position of the ICZ framework. This structural modification effectively improves the molecular π-π packing, thereby promoting the improvement of electron transfer and significantly enhancing the output of ECL. The ECL behavior of a series of modified ICZ compounds was systematically characterized. The luminescence mechanism was investigated using ECL spectroscopy, and the associated electron transfer dynamics were quantitatively investigated using intensity-modulated photocurrent spectroscopy and scanning photoelectrochemical microscopy. This dual analytical approach offers new mechanistic insights into the ECL process. Finally, the optimized ICZ-based luminophore was successfully used in the sensitive detection of dichromate ions (Cr₂O₇^2-) in water samples from the Yellow River, demonstrating its potential in environmental monitoring applications.