The electron–hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots (Cdots) is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π –π * states of the sp2 domains decreases as the sp2 cluster size increases. More importantly, the strong electron–hole exchange interaction results in the splitting of the exciton states of the sp2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE , which decreases with increasing sp2 cluster size owing to the reduction of the confinement energy and the suppression of the electron–hole exchange interaction.