Intramolecular orbital interactions in 9,10-disilatriptycene studied by photoelectron spectroscopy

9,10-Disilatriptycene is of high symmetry and structurally very close to triptycene. In the latter case it is known that the through-space orbital interactions among the π electron systems of the three benzene rings predominate, the effect of the through-bond interactions being negligibly small. In this study, the vapor-phase He(I) photoelectron spectra of triptycene and 9,10-disilatriptycene were measured and studied comparatively in order to investigate the relative importance of the Jahn-Teller effects in the cationic states of these compounds, the through-space and the through-bond interactions. Simple LCBO model calculations could reproduce almost quantitatively the features of their observed spectral patterns. The spectral pattern is quite complex in 9,10-disilatriptycene in contrast to that of triptycene due to the back-donation from the benzene rings to the Si atoms in addition to the Jahn-Teller effects in the cationic states and the through-space interactions.