Optical properties of graphene quantum dots: the role of chiral symmetry

TL;DR

This study investigates how chiral symmetry influences the electronic and optical behaviors of graphene quantum dots, revealing that edge functionalization can modify their fluorescence by affecting low-energy excitations.

Contribution

It provides a detailed ab initio analysis linking chiral symmetry and edge functionalization to optical properties of GQDs, a novel insight into their photoluminescence mechanisms.

Findings

Pristine GQDs exhibit dark low-energy singlet excitations that suppress fluorescence.

Edge sp³ functionalization brightens low-lying excitations by disrupting planar symmetry.

Chiral symmetry plays a key role in the optical properties of GQDs.

Abstract

We analyse the electronic and optical properties of graphene quantum dots (GQD) using accurate \textit{ab initio} many-body $GW$ and Bethe-Salpeter calculations. We show that most pristine GQD, including structures with irregular shapes, are characterized by dark low energy singlet excitations that quench fluorescence. We rationalizqe this property by exploiting the chiral symmetry of the low energy electronic states in graphene. Edge \textit{sp}$^3$ functionalization is shown to efficiently brighten these low lying excitations by distorting the \textit{sp}$^2$ backbone planar symmetry. Such findings reveal an original indirect scenario for the influence of functionalization on the photoluminescence properties.