We investigate the optical absorption spectra of aromatic isothianaphthene oligomers, from the monomer up to the tetramer, with a combined theoretical and experimental approach. Geometry optimizations are performed with the semiempirical Austin Model 1 method on disilylated isothianaphthene oligomers of increasing chain length. The calculated geometric parameters are compared to those obtianed from the single-crystal structure of the 3, 3'-bis ...