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 obtained from the single-crystal structure of the 3,3’-bis(tert-butyldimethylsilyl)-1,1’-biisothianaphthene. We then use the intermediate neglect of differential overlap method, coupled to single configuration interaction, to simulate theoretically the optical absorption spectra of the oligomers. The corresponding experimental spectra are recorded in n-hexane solution, and their evolution with chain length is discussed on the basis of the theoretical data.