The optoelectronic properties of functionalized graphene quantum dots (GQDs) have been explored by simulating electronic structure of three different shapes of GQDs containing exclusively zigzag or armchair edges in both pristine and functionalized forms. Absorption spectra and transition densities for the low-lying excited states are evaluated by using time-dependent density functional theory and compared for different functionalization species. The functionalization position dictates the optical properties of square GQDs, where isomers with CH₂ in the intermediate positions (excluding corner and center positions) have higher electronic transition energies and exciton delocalization than other isomers. Rhombic GQDs with all armchair edges exhibit high steric flexibility, and their complete passivation results in the largest structural deformation from planarity and strongest red-shifts. A steady red-shift in the absorption energy is observed following the order F, CH₃, Cl, and Br substitutions. This suggests that the steric effects due to large van der Waals radii overcome electronegative effects.

中文翻译：

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石墨烯量子点边缘形态对其光学性质的影响

通过模拟三种不同形状的 GQD 的电子结构，探索了功能化石墨烯量子点 (GQD) 的光电特性，这些 GQD 仅包含原始和功能化形式的锯齿形或扶手椅边缘。低位激发态的吸收光谱和跃迁密度通过使用时间相关的密度泛函理论进行评估，并针对不同的功能化物质进行比较。官能化位置决定了方形 GQD 的光学性质，其中 CH _{2的异构体}在中间位置（不包括角落和中心位置）具有比其他异构体更高的电子跃迁能和激子离域。具有所有扶手椅边缘的菱形 GQD 表现出高空间柔性，并且它们的完全钝化导致平面性的最大结构变形和最强的红移。_{在 F、CH 3}、Cl 和 Br 取代之后观察到吸收能量的稳定红移。这表明由于大范德华半径引起的空间效应克服了负电效应。