Exploring optoelectronic properties of undoped and amine-doped carbon dots: Impact of surface functionalization and pH

Tuning optoelectronic properties through surface modifications and doping in low dimensional carbon dots (CDs) has been an asset in designing them for versatile applications. In this article, we explore the modulations in photophysical and charge transport characteristics of doped and undoped CDs functionalized with redox-active dopamine (DA). The pH-dependent DA chemistry on the surface of CDs is observed to have deterring effect on excited state dynamics with superior charge transfer efficiency for pristine CDs compared with the doped one. Charge transport studies through conducting measurements across electrode-CDs-electrode junction report a pH -induced current enhancement with DA functionalization resulting from a shifted equilibrium among the reduced (hydroquinone) and oxidized (quinone) isomers of DA. While the changes in the optical and electronic features are significantly perturbed with pH for the DA-treated undoped CDs, nominal alterations in spectral features are reported for the doped ones. The current-voltage conductance across the junctions is influenced by surface -treated CDs for acidic pH, with signatures of direct tunneling for a low bias regime, curtailing the Fowler-Nordheim (FN) tunneling. These features can have immediate optoelectronic-based applications in pH-based sensors and molecular electronics.