Stability and electronic spectroscopy of isomers for C74Si2

Equilibrium structures and relative stabilities of possible lower-energy isomers for C74Si2 base on C76(D2) were studied using semi-empirical INDO series of methods. Full optimization indicated that the most stable geometry was 39,60-C74Si2 where two silicon atoms were immediate neighbors and located at the bond between a five- and a six-membered rings near the longest C2(Z) axis of C76 and was less stable than C76. Fixing one Si atom, the other Si atom was used to substitute different carbon atoms with different Y Cartesian coordinates. It was found that total energy was related to Y coordinate values and became higher when two Si atoms were separated from each other. Based on the optimized geometries, the electronic spectroscopy of C74Si2 was investigated with the INDO/CIS method and long-waved absorption peaks appeared in the NIR region. The electronic transition and red-shift of absorptions of C74Si2 compared with that of C76 were discussed.