Bottom-up carbon dots: purification, single-particle dynamics, and electronic structure.

The physico-chemical properties of 'bottom-up' carbon dots synthesized from small molecules feature both generalities, such as sp-networked carbon and core-surface energy transfer, and heterogeneities, due to the unpredictable location of heteroatoms and often non-crystalline structure. Here we focus our review on three aspects of these systems: (1) coupling characterization with bottom-up synthesis to identify and remove confounding byproducts such as small molecules or hydrogen-rich polymers; (2) single-particle characterization to obtain unambiguous information on carbon dots and highlight the distribution of properties around the ensemble average; (3) electronic structure of carbon dots and how it can help elucidate the origin of important properties such as optical absorption and fluorescence from a heterogeneous ensemble of carbon dots.