Tunable Optical Features of Graphene Quantum Dots from Edge Functionalization

Abstract

Graphene quantum dots (GQDs) are promising semiconducting materials for practical applications. Chemical functionalization of GQD edges is a strategy to increase their solubility and processability and to modify their optical properties. Such functionalization has a twofold effect on the electronic structure, both attributed to electronic spatial localization. The first is relevant to the introduction of electronegative species, whereas the second effect modifies the electron wave function spatial distribution through the conformational changes of geometry of the otherwise planar GQD backbone. Our computational study shows that functionalization with a weakly electronegative chlorine functional group induces small red-shifts due to the localization of excitonic states around the defect site. Groups with strong electron inducting ability such as nitro introduce stronger red-shifts. In both cases, the planar geometry of the pristine sheet is preserved when functionalization is performed at only a single site. However, functionalizing at multiple sites around the edge results in warping of the geometry of the GQD, leading to stronger electronic localizations and the largest red-shifts. This observation suggests the utility of controlling the planar geometry as a new strategy for chemically modifying 2-dimensional nanomaterials toward optical tuning.

Nature of electronic excitations in small non-stoichiometric quantum dots

“…Given the presence of a dielectric medium around a QD, the energetics of the surface-associated orbitals get stabilized, leading to the removal of the in-gap states and thereby often increasing the oscillator strengths of the lowest transitions. 31,47–49 Chemically, the overall non-zero charge of a non-stoichiometric QD can usually be compensated by charge-neutralizing ligands on the QD surface. However, from the modeling perspective, the availability of multiple sites on the QD surface for ligand placement significantly increases the complexity and structure diversity as these sites are non-identical in terms of ligand binding.…”

Structural defects in graphene quantum dots: A review

“…Structure of graphene quantum dots (GQDs) with defect sites on the edges for functionalization [178]…”

“…F I G U R E 1 5 Structure of graphene quantum dots (GQDs) with defect sites on the edges for functionalization [178] 4 | APPLICATIONS OF DEFECT-RICH GQDS…”

“…These properties get hindered due to the presence of defect sites around the edges. The sites, which have been basically chosen to functionalize in the work of Sheely et al [178] have been depicted in Figure 15. Those sites have been located as defect sites at the edges, which require functionalization for appropriate control of defects.…”

Graphene Quantum Dots-Based Nanocomposites Applied in Electrochemical Sensors: A Recent Survey

“…Furthermore, the preference for GQDs with an enhanced edge effect or larger basal planes can be tailored depending on the methodology of functionalization employed. Some groups have a preference for tailoring the core, while others for the edge sites [145][146][147]. As a consequence, elucidating the complete effect of core size and the edges of the GQDs in electrochemical applications has not yet been fully achieved, although some important contributions have been provided in the literature [118,148,149].…”