The roles of intermediate fluorophores on the optical properties of bottom-up synthesized carbon nanodots

Carbon nanodots (CNDs) are the latest nano-sized carbon materials having unique properties such as biocompatible, highly photoluminescent, and nontoxic which are suitable for diverse applications including lighting, sensing, bioimaging, and biochemical analyzing. CNDs could be synthesized by top-down methods in which graphite is fragmented into nano-sized graphene dots. Alternatively, CNDs could be formed by a bottom-up synthetic strategy where organic molecules are fused together via complex condensation and carbonization processes. Although a great number of organic molecules have been used successfully to prepare CNDs there are very few CNDs that exhibit the quantum size effects. The absorption and emission properties of bottom-up synthesized CNDs rely vastly on molecular-like fluorophores which are the intermediates formed during the fusion of molecular precursors and are incorporated into CNDs in the later states of carbonization processes. This review aims to demonstrate recent understandings on the formation of intermediate fluorophores and their contribution to the optical properties of CNDs.