Molecular Insights of Carbon Nanodot Formation and Their Two-Photon Emission Properties

The structure formation of carbon nanodots (C-dots) prepared from three different organic precursors is discussed at the molecular level. During microwave synthesis, organic chromophores associated with C-dot structures are formed that exhibit distinct optical features. We have elucidated the molecular structure of these fluorophores and investigated their optical properties with and without the C-dots. The emergence of two-photon emission was observed and correlated with the hybridization state of the carbon atoms within the C-dot as well as the formation of the fluorophores. Varying contents of sp2 and sp3 hybridization in different C-dots also affects their one-photon and two-photon emission characteristics. Understanding the molecular structure of the
carbon nanocore and the organic fluorophores formed in C-dots would enable rational design of C-dots with improved optical features, which would be of great relevance for their applications, for example, in bioimaging.