Enhanced fluorescence emission or singlet oxygen production of cationic porphyrazines and porphyrins through combination with carbon dots.

Abstract

A cationic porphyrin and porphyrazine with the 3-ethylpyridyl substituent (H₂P and H₂Pz) and their respective zinc complexes (ZnP and ZnPz) were assembled to a carbon dot (CD) synthesized from citric acid and ammonium citrate. A titration was performed using a fluorescence spectrophotometer to determine the stoichiometric ratio at which the maximum interaction between the substances occurs, as well as the Stern-Volmer constant and intrinsic binding constant. The combination between CD and porphyrins or porphyrazines was confirmed using UV-VIS absorption spectroscopy, fluorescence emission, zeta potential, and Diffusion-Ordered NMR Spectroscopy (DOSY). It was observed that after combination, there is a decline in the absorption of porphyrin derivatives, a variation in the emission of porphyrazines, a subtle increase in the zeta potential compared to the isolated CD particles, and a variation in the translational diffusion coefficient. It was also found that upon combination with the CD, changes in the photophysical properties of the macrocycles occur, for example, the fluorescence quantum yield of H₂Pz increases from 0.81 ± 0.03% to 1.97 ± 0.05% while the singlet oxygen quantum yield of H₂P increases ca. 70%. These results exemplify the capacity of CD to boost some properties of photosensitizers that are key for photodynamic therapy applications.