Effects of size, shape, and functionalization on the electronic and optical properties of graphene quantum dots

Graphene quantum dots (GQDs) exhibit size-dependent optical properties arising from quantum confinement, making them promising materials for applications in optoelectronics, bioimaging, sensing, photocatalysis, and energy conversion. In this work, density functional theory (DFT), time-dependent DFT (TD-DFT), and quantitative structure–property relationship (QSPR) approaches were combined to investigate the effects of size, shape, and amine functionalization on the electronic and optical properties of armchair-edged GQDs. The results showed that increasing GQD size reduced the energy gap and produced a systematic red shift in optical absorption. Triangular and hexagonal shape GQDs exhibited similar size-dependent trends, indicating that quantum confinement dominates over geometric shape effects. Amine functionalization further modulated the optical response by altering the electronic structure and transition characteristics. QSPR models developed for the wavelength and oscillator strength of the lowest-energy electronic transition achieved good predictive performance. These findings provide useful structure–property relationships for the rational design of GQD-based optoelectronic materials.