Precursor Engineering towards Orange and Red-Emissive Carbon Dots for LEDs with Tunable Emission Colors

Abstract

Carbon dots (CDs) have been of great interest due to their high potential in optoelectronic applications. Although various CDs have been synthesized via the “bottom-up” pathway, fewer focused on understanding the origins of the structural and optical diversities of CDs. In this work, two benzenoid acids with a slight structural variation (i.e., 9-oxo-9H-fluorene-2,7-dicarboxylic acid (FR) and 4,4'-biphenyl dicarboxylic acid (BP)) are employed as precursors, yielding orange and red-emissive CDs, respectively, with quantum yields of 43.1 ~ 30.9%. A combined experimental and theoretical study reveals that these CDs’ structural and optical diversities originate from the structural variation of precursors. Furthermore, we demonstrate that the light-emitting diodes (LEDs) based on the blended emissive layer of poly(N-vinyl carbazole) (PVK) and CDs display cyan and yellow lights, respectively, with moderate turn-on voltages of 4.0/4.5 V and maximum luminances of 454/276 cd m-2. Such different optoelectronic performances could be attributable to the different energy-level alignments of CDs-FR and CDs-BP. This study thus provides a typical example to understand the precursor-dependent diversities of CDs, which may contribute to the rational screening of precursors towards the CDs with desirable optical/optoelectronic properties.