Size Inhomogeneity Facilitates Exciton Dissociation in Carbon Dots

Organic carbon dots (CDs) exhibit tunable electronic structures and exceptional optical properties, supporting both exciton- and charge-driven applications. However, the mechanisms underlying this dual functionality are poorly understood. This study establishes the role of size inhomogeneity in exciton dissociation for the first time. Two distinct CD types were identified, each class with a size deviation. Intradot relaxation within the same type of CDs composes of a fast (∼1 ps) and a slow (∼tens of picoseconds) component among size-deviated subpopulations. Interdot exciton transfer between two types of CDs occurs with a time scale of 4.4 ps but is evident only when the CDs with higher-energy states are excited. It also facilitates exciton dissociation, generating nearly free carriers, confirmed by EPR spectra (g-value = 2.005). These findings highlight the critical role of energy level alignment and selective excitation in mediating exciton dissociation, providing key insights for optimizing CDs in light emission and energy conversion applications.