Mechanistic Insights into Photoluminescence Regulation in the Photoinduced Electron Transfer System of Carbon Dots and Benzoquinone Molecules

Chemical sensing and bioimaging based on carbon dots (CDs) heavily rely on a fundamental understanding of photoluminescence (PL) behavior and regulation. This work aims to provide mechanistic insights into PL regulation in the photoinduced electron transfer (PET) system consisting of CDs and benzoquinone (BQ) molecules, placing emphasis on how the specific surface functionalization of CDs in a controlled manner affects the PET process and its related PL regulation. Two contrasting PET systems of CDs(p)-BQ and CDs(r)-BQ (with BQ acting as an electron acceptor) are deliberately constructed, in which CDs(p) and CDs(r) have relatively poor and rich carboxyl groups anchored on their surfaces, respectively. As revealed by ultrafast transient absorption spectroscopy, their CDs-to-BQ PET variations with BQ concentration exhibit quite different trends─a trivial "single" linear dependence for the CDs(p)-BQ system vs a nontrivial "dual" linear dependence featuring a critical turning point for the CDs(r)-BQ system. Such a distinct difference can be connected to the different situations of hydrogen-bonding-mediated formation of a ground-state complex between CDs and BQ, thereby distinguishing the PL quenching regimes between the two PET systems─dynamic quenching alone for the CDs(p)-BQ system vs combined dynamic/static quenching for the CDs(r)-BQ system. This study sheds light on the critical role of surface engineering in targeted and effective PL regulation in CD-based PET systems.