Heavy atom effect in carbon dots: Enhanced photosensitization performance for visual detection of copper ions

The incorporation of heavy atoms into fluorescent emitters can efficiently facilitate spin-orbit coupling and enhance the intersystem crossing process from excited singlet states to triplet states. However, the introduction of heavy atoms into carbon dots (CDs) materials still remains challenges. In this work, CDs synthesized from polyethyleneimine and itaconic acid were subjected to a mild bromination process, yielding bromine-doped carbon dots (Br-CDs). Bromine atoms significantly enhanced the intersystem crossing process, leading to a 155.1 % increase in the phosphorescence intensity of the CDs. Moreover, the enhanced generation of excited triplet states endowed the Br-CDs with photosensitization performance, enabling them to produce singlet oxygen and superoxide anion radicals upon light irradiation. Interestingly, it was found that Cu 2+ ions could effectively inhibit this photosensitization process. By integrating the color changes of photosensitization oxidation substrates, a colorimetric method was developed for the rapid determination of Cu 2+ ion concentrations in water samples. This proposed method offers a novel approach for the design of sensors based on luminescent nanomaterials.