Unconventional aliphatic fluorophores discovered as the luminescence origin in citric acid-urea carbon dots

Carbon dots (CDs) are emerging as the material of choice in a range of applications due to their excellent photoluminescence properties, ease of preparation from inexpensive precursors, and low toxicity. However, the precise nature of the mechanism for the fluorescence is still under debate, and several molecular fluorophores have been reported. In this work, a new blue fluorophore, 5-oxopyrrolidine-3-carboxylic acid, was discovered in carbon dots synthesized from the most commonly used precursors: citric acid and urea. The molecular product alone has demonstrated interesting aggregation-enhanced emission (AEE), making it unique compared to other fluorophores known to be generated in CDs. We propose that this molecular fluorophore is associated with a polymer backbone within the CDs, and its fluorescence behavior is largely dependent on intermolecular interactions with the polymers or other fluorophores. Thus, a new class of non-traditional fluorophores is now relevant to the consideration of the CD fluorescence mechanism, providing both an additional challenge to the community in resolving the mechanism and an opportunity for a greater range of CD design schemes and applications.

Automated summary

Carbon dots (CDs) are a desirable material for various applications due to their excellent photoluminescence properties, inexpensive preparation, and low toxicity. The mechanism for fluorescence in CDs is still debated, and a new blue fluorophore called 5-oxopyrrolidine-3-carboxylic acid has been discovered in CDs synthesized from commonly used precursors. This molecular fluorophore demonstrates aggregation-enhanced emission (AEE), which is unique compared to other known fluorophores in CDs.