A computational approach to the study of carbon nanodots for the determination of their structure and properties

Recently, carbon nanodots (CNDs) have attracted considerable attention in the field of carbon-based nanoparticles due to their unique properties: intense photoluminescence, low toxicity, excellent biocompatibility and easy surface functionalization [1]. Their synthesis employs straightforward bottom-up and top-down methods, which dictate the functional groups present on their surface, their size and their photoluminescent response [2]. As a result, CNDs have found numerous applications, particularly in biological and biomedical fields [3]. However, a comprehensive understanding of their atomic-level structure and its correlation with their properties remains incomplete [4]. The challenge lies in identifying more effective starting models than the ones currently used, which are mostly based on polycyclic aromatic hydrocarbons (PAHs) [5]. The development of an efficient computational method is therefore required to fill these gaps. Preferably, this approach should maintain an explicit description of the electronic degrees of freedom, to assess optical properties from first principles and to investigate electron density and, ultimately, the surface charge of the nanoparticle. Here, we present results on the application of a computational multiscale approach based on ab-initio DFT (Density Functional Theory) and semi-empirical (TB-DFT, tight-binding density functional theory) methods to the class of CNDs. The advantage lies in reducing time and cost of the research compared to experimental methods, while considering a wide range of structures and maintaining a good level of accuracy. We explored different ways to generate the model structures, considering carbon clusters as a good starting point for our study. Our investigation focuses on CNDs with an amorphous carbogenic core, which is the less explored variant in the literature. Several model structures based on amorphous carbon functionalized with various nitrogen-based groups have been studied and will be presented. In addition, the relationship between their structure and properties has been explored using TD-DFT (time-dependent density functional theory), obtaining the optical properties of a selected number of carbon clusters, both in the pure and N-doped form. References [1] D. Ozyurt, M. Al Kobaisi, R. K. Hocking and B. Fox, Carbon Trends. 12. (2023). 100276. [2] B. Yao, H. Huang, Y. Liu and Z. Kang, Trends in Chemistry. 1 (2). (2019). 235. [3] J. Liu, R. Li and B. Yang, ACS Central Science. 6 (12). (2020). 2179. [4] K. J. Mintz et al., Carbon. 173. (2021). 433. [5] M. Langer et al., App. Mat. Today. 22. (2021). 100924.