Computational Studies on the Structures of Nanographenes with Various Edge Functionalities.

Area of Science:

• Materials Science
• Computational Chemistry
• Nanotechnology

Background:

• Experimental observations suggest armchair-edged nanographenes (NGs) with carboxyl groups are dominant.
• Previous computational studies often focused on hydrogen-terminated NGs, which differ from experimental findings.

Purpose of the Study:

• To computationally investigate nanographenes (NGs) with various sizes and edge terminations (hydrogen, carboxy, N-methyl imide).
• To compare computational and experimental UV-vis spectra to understand electronic properties and solubility.
• To reconcile discrepancies between theoretical models and experimental data for NGs.

Main Methods:

• Density Functional Theory (DFT) calculations were employed for NGs of varying sizes (C42 to C174).
• Simulations included hydrogen, carboxy, and N-methyl imide terminated armchair edges.
• UV-vis spectra were calculated and compared with experimental data for carboxy- and N-octadecyl chain terminated NGs.

Main Results:

• DFT calculations revealed distorted basal planes but similar HOMO-LUMO gaps across different edge functionalizations.
• Edge oxidation and functionalization showed minimal influence on the electronic structure.
• Comparison of calculated and observed UV-vis spectra confirmed the contribution of π-π* transitions to visible light absorption.
• Dimeric NG structures indicated that basal plane distortion and steric hindrance widen surface-to-surface distances, facilitating solvent molecule intercalation.

Conclusions:

• Edge functionalization and oxidation have a limited impact on the electronic properties of nanographenes.
• Distorted basal planes and steric effects of functional groups enhance NG solubility by allowing solvent penetration.
• Computational models are refined to better match experimental observations of nanographene properties.