NITROGEN EFFECT ON ABSORPTION SPECTRUM IN CARBON DOTS : A TIME-DEPENDENT DENSITY FUNCTIONAL THEORY STUDY

• Main Author: Rahmatiya Hasna, Wifda
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/52960
• Institution: Institut Teknologi Bandung

The structure of carbon dots (CDs) is still a debate topic because it is thought to be very complex. This case has an impact on the difficulties of researchers in their field of conducting an experimental analysis. Besides, several CDs that have new characteristics add to the mystery of the complexity of their structure. One type of CDs is reported to have new optical properties in the form of UV-Vis absorbance capability in the near-infrared (NIR) spectrum, which opens up new potential applications in photothermal cancer therapy. Experimentally, the new absorbance ability is thought to be closely related to the C-N configuration of the structure. However, further studies are still needed to determine the source of the absorbance properties of NIR. Therefore, in this study, a time-dependent density functional theory (TD-DFT) was calculated on CDs material doped with nitrogen atoms to evaluate the NIR range's absorbance properties. TD-DFT calculations were carried out with the help of Gaussian 09 software using the correlation function B3LYP and basis 6-311G**. The benzena ring structure was used as a model for the structure of the CDs. Then several structural variations are carried out, such as variations in the number of benzena rings, variations in the C-N configuration (pyrrolic-N, pyridinic-N, and graphitic-N), and variations in the position of nitrogen (N) atoms in the pyrrolic-N configuration. Computational calculations include the process of geometry optimization and the calculation of time-dependent density functional theory (TD-DFT) to obtain the value of excitation energy and the value of oscillator strength to study the absorbance characteristics of CDs. The calculation results show that the more benzena rings (the larger the CDs diameter), the bandgap CDs value from the computation results is closer to the experimental value. Interestingly, the TD-DFT study results show that new absorbance properties in the NIR range of CDs material are obtained for the CDs structure in the presence of a pyrrolic-N configuration with a center-site position. This is also consistent with our group experiment results, where the absorbance properties of NIR in CDs material were only observed in CDs material with pyrrolic-N dominance.