Are carbon dots cluster-triggered luminogens? How through-space interaction arrangement influence the optical properties of carbon dots

The use of non-conventional luminescent materials without conjugated chromophores, known as cluster-triggered emission materials (CLgens), has attracted considerable attention as an environmentally benign and biocompatible alternative to conventional fluorophores. A major challenge in developing these materials is the limited understanding of the mechanisms that govern the formation and fate of their excitons, in particular the interaction of the clusters with each other and their surroundings. In this regard, this study aims to gain insight into this mechanism by unravelling the optical properties of the cluster through an innovative approach where a non-traditional luminescent polymer is converted into carbonized polymer dots (CPDs), allowing tuning of electronic interactions and cluster stiffening. The formation of this type of CPDs leads to an increase in through-space interactions (TSI) when compared to the polymer precursor, driven by stronger spatial interactions enabled by the reduced distances and constraints inherent in the formation of the CPDs. Even more striking were the small differences in spectral features between the precursors and CPDs. The typical spectroscopic features associated with TSI, such as the different excitation and absorption spectra, dependence of the emission spectra on the excitation wavelength, and blue-shift emission in small clusters, were also observed. These observations can only lead to the conclusion that TSI is the most plausible mechanism for the luminescence of these CPDs. This represents a significant breakthrough in understanding the relationship between CLgens and the derived CPDs. Furthermore, it highlights the importance of considering the properties of the precursor in order to avoid misconceptions about the luminescence of these materials, and to adjust their properties accordingly.