Electronic interaction-enhanced NO photorelease and photothermal conversion in N-doped carbon dot nanoconjugates

A nitric oxide (NO) photodonor (1) capable of releasing two NO molecules through a stepwise mechanism has been covalently grafted to blue-emitting N-doped carbon dots (NCDs). The resulting water-soluble nanoconjugate (NCDs-1), ca. 10 nm in diameter, exhibits a new absorption band not present in the simple physical mixture of the two components and is attributable to strong electronic interactions between them in the ground state. Blue light excitation of NCDs-1 leads to NO photogeneration with an efficiency almost one order of magnitude higher than that observed for 1 alone, probably due to a photoinduced electron transfer between the NCDs and the grafted 1. Photoexcitation of the nanoconjugate also results in effective photothermal conversion, which is negligible in the naked NCDs. Furthermore, in contrast to 1, the nanoconjugate liberates NO also under excitation with green light. Finally, the typical blue fluorescence of the NCDs is quenched in NCDs-1 but restored upon the photouncaging of the second NO molecule, providing readable and real-time information about the amount of NO photogenerated. A strong electronic interaction between N-doped carbon dots and an NO photodonor grafted on their surface leads to significant enhancement of NO photorelease and photothermal conversion efficiencies.