Properties of Carbon Dots versus Small Molecules from “Bottom-up” Synthesis

Zhengyi Bian, Alison Wallum, Arshad Mehmood, Eric Gomez, Ziwen Wang, Subhendu Pandit, Shuming Nie, Stephan Link, Benjamin G. Levine, Martin Gruebele

Research output: Contribution to journalArticlepeer-review


A major challenge in the “bottom-up” solvothermal synthesis of carbon dots (CDs) is the removal of small-molecule byproducts, noncarbonized polyamides, or other impurities that confound the optical properties. In previously reported benzene diamine-based CDs, the observed fluorescence signal already has been shown to arise from free small molecules, not from nanosized carbonized dots. Here we have unambiguously identified the small-molecule species in the synthesis of CDs starting with several isomers of benzene diamine by directly matching their NMR, mass spectrometry, and optical data with commercially available small organic molecules. By combining dialysis and chromatography, we have sufficiently purified the CD reaction mixtures to measure the CD size by TEM and STM, elemental composition, optical absorption and emission, and single-particle blinking dynamics. The results can be rationalized by electronic structure calculations on small model CDs. Our results conclusively show that the purified benzene diamine-based CDs do not emit red fluorescence, so the quest for full-spectrum fluorescence from isomers of a single precursor molecule remains open.

Original languageEnglish (US)
Pages (from-to)22788-22799
Number of pages12
JournalACS Nano
Issue number22
StatePublished - Nov 28 2023


  • carbon dots
  • fluorescence
  • fluorescence mechanism
  • organic fluorophore
  • STM

ASJC Scopus subject areas

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy


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