Photostable carbon dots with intense green emission in an open reactor synthesis

Carbon dots (CDs) are novel fluorescent nanoparticles that combine intense emission of visible light with eco-friendly and inexpensive carbon-based composition. In this work, CDs are synthesized trough a glycothermal treatment of resorcinol (1,3-hydroxybenzene) in air atmosphere. The presence of catalysts (NaOH and H2SO4) increases the reaction rate, promoting a faster and massive production of nanoparticles. The spectroscopic monitoring of fluorescence during CD synthesis, supported by a DFT study, allows to depict the formation and structural evolution of OH terminated polycyclic aromatic hydrocarbons (PAHs) from resorcinol polycondensation. In purified CDs, PAHs embedded in the amorphous carbogenic core are responsible for an intense green fluorescence emission with a quantum yield up to ∼40%. Such band exhibits high resistance to UV photobleaching, attributed to the physical protection of the carbogenic matrix. Finally, adding a strong acid/base to the CD solution, the CD fluorescence can be cyclically quenched/restored (due to reversible aggregation), suggesting the convenient use of such CDs in on/off sensors or stimulus-responding devices.