Photoinduced Electron Transfer Mediated by Coordination between Carboxyl on Carbon Nanodots and Cu2+ Quenching Photoluminescence

Carbon nanodots (C-dots) have been widely used in sensing, such as detection of ions, small molecules and biomolecules, based on their photoluminescence (PL) quenching by metal ions. Though C-dots prepared by different methods exhibited various sensitives to metal ions, it is labor intensiveness and time-consuming for selecting synthetic route to obtain C-dots that meet requirements of practical applications. Hence, for the high selective and sensitive applications of C-dots, it is the effective approach to reveal the structure–property relationships in the quenching process. Herein, we present an insight into the mechanism of the PL quenching of C-dots by Cu2+. According to the results of PL, UV–vis absorption, time-resolved PL, and femtosecond transient absorbance measurements, we confirmed that the quenching occurs by a photoinduced electron transfer (PET) process from the photoexcited C-dots to the empty d orbits of Cu2+ combining with C-dots. Meanwhile, through separate protecting functional groups on the surface of C-dots, the structure of C-dots coordinating with Cu2+ is revealed to be carboxyl rather than hydroxyl groups. This study leads to a better understanding of the quenching of C-dots and takes an important step toward more rational design of C-dots-based sensor with high performance.