Optical absorption tensors based on C$_{70}$ trimers and polymers

Abstract

The optical absorption spectrum of $C_{60}$-dimers and polymers was investigated by Kikuo et al. in 1996\cite{harigaya1996charge}. As a compliment to these earlier studies, the optical absorption spectrum of the $C_{70}$ fullerene has been investigated in the present study. The main purpose was then to compare the absorption spectrum of the $C_{70}$-dimers and trimers and, more specifically, to clarify the effect of these molecular structures on the absorption spectrum. What is most important and decisive is then the value of the conjugation parameter of these $C_{70}$-based molecules. In the present study, a tight-binding model was used in calculating the optical absorption spectra of both $C_{70}$ dimers and polymers, as well as $C_{70}$ trimers and polymers. The change in conjugation parameter for each of these species was found to cause variations in the corresponding optical absorption spectrum. It was found that the absorption tensor of the $C_{70}$ trimer and the polymer was, depending on the value of the conjugation parameters $b=0.5$ and $b=0.8$. The situation was almost the same for the conjugation parameters $b=0.1$ and $b=0.2$. In addition, the value of the band gap was also different depending on the different conjugation parameters, with a reduced value for the larger values of this parameter. As a conclusion, smaller values of the conjugation parameter were not found to have a large effect on the absorption spectrum of the $C_{70}$-dimers and trimers, or in other words, the effect was hardly visible. On the contrary, the larger values caused a drastic change in the optical absorption spectrum of the $C_{70}$-dimers and trimers.