Experimental and Time-Dependent Density Functional Theory Modeling Studies on the Optical Properties of Carbon Nanodots

Carbon nanodots (CNDs) are zero-dimensional carbon particles that have attracted interest in a variety of applications mostly because of their small size, structure-function versatility, and photo-luminescence properties. Unfortunately, the complicated and varied structures of particles that fall under the umbrella of CNDs make prediction of the optical properties difficult to determine empirically. It is thus far more practical to use computational methods, such as density functional theory (DFT), to predict the optical properties of different potential structures. Herein, two different syntheses of CNDs with noticeably different optical properties are presented for demonstration. Time-dependent DFT on twelve different proposed structures was then performed in order to elucidate the nature of the absorptive properties. The main result of these calculations is that deformations in the graphitic structure of CNDs seem to dominate the effects on the optical transitions, particularly the pi-pi* transitions, in comparison with experimental results.