Structural study of B-N Co-doped carbon dots: Comparison of spectroscopic analysis using DFT

Abstract

Understanding the internal geometric structure of boron–nitrogen (B–N) Co-doped carbon dots (CDs) is crucial for tailoring their properties to meet the requirements of advanced applications in bioimaging, sensing, and photovoltaics. In this study, a comprehensive Density Functional Theory (DFT) analysis was conducted to investigate the formation and arrangement of individual layers within B–N Co-doped CDs—an area that remains insufficiently explored. Thirteen distinct putative ground-state geometries were identified using the B3LYP/6-31G* level of theory. These structures were selected based on experimental insights into the material’s chemistry and correspond to low-energy local minima. While they may not represent the absolute minimum configuration, they are physically plausible and relevant for modeling the diversity of bonding environments within B–N Co-doped CDs. Comparison between theoretical and experimental FTIR and Raman spectra revealed that no single structure fully accounts for the observed spectral features. However, a composite model—constructed by combining spectra from several low-energy configurations with assumed equal statistical weight—showed significantly improved agreement with experimental data. These results suggest that B–N Co-doped CDs exhibit a heterogeneous internal architecture composed of a mixture of closely related molecular structures. This work provides new insights into the structural complexity of doped carbon dots. It offers a solid theoretical basis for guiding future efforts to optimize their electronic and optical properties for a broad range of technological applications.