Optical absorption tensors based on C70 trimers and polymers

Abstract

The optical absorption spectra of C60-dimers and polymers were investigated by Kikuo et al. in 1996 (Harigaya, 1996). As a complement to these earlier studies, the optical absorption spectrum of the C70 fullerene has been investigated in the present study. The main purpose was then to compare the absorption spectra of the C70 dimers and trimers and, more specifically, to clarify the effect of these molecular structures on their absorption spectra. What was most important and decisive was the importance of the conjugation parameter of these C70-based molecules. A tight-binding model was used in calculating the optical absorption spectra of both C70 dimers and polymers, as well as of the C70 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 tensors of the C70 trimer and polymer depended on the value of the conjugation parameters (b=0.5 and b=0.8). However, the optical absorption spectrum 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 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 spectra of the C70 dimers and trimers, or in other words, the effect was hardly visible. On the contrary, the larger values caused drastic changes in the optical absorption spectra of the C70 dimers and trimers.