Regulating optoelectronics of carbon dots with redox-active dopamine

Abstract

The electron transfer (ET) processes in carbon-based quantum dots (CDs) have laid to extensive research endeavors due to their tunable optoelectronic properties with alteration in surface functionalization, doping, surface charge, etc. Here, we proffer shreds of evidence on pH-dependent electron transfer and transport properties of undoped CDs (UCDs) and amine-doped CDs (ACDs) with a redox-active neurotransmitter, dopamine (DA). A pronounced pH-dependent photoluminescence (PL) quenching is depicted for both the CDs with DA, where the quenching efficiency substantially increases in alkaline solvents. Taking advantage of the structural transformation of DA from hydroquinone to quinone, the electron accepting capacity can be improved for alkaline pH, which enhances the ET efficiency. The pH-regulated conductance measurements across the metal-CD-metal junction reveal a hike in the conductivity for acidic and alkaline pH relative to the neutral one. The I-V traces of UCDs and ACDs are contributed by an initial linear current rise and non-linear growth at higher bias explicating both direct and Fowler-Nordheim (F-N) tunneling mechanisms. In addition, the incorporation of DA into these CDs, not only significantly increases conductance in all pH media but also enables them to tunnel the potential barrier directly in acidic media, reducing F-N tunneling. These results could provide new avenues for developing reliable optoelectronic devices and sensing probes for a wide range of applications.