We have carried out experiments to determine the extent of dπ–pπ interaction in silylnaphthalenes by examining a series of SiMe3 and CMe3 substituted naphthalenes using the techniques of polarography, and charge transfer and u.v. spectroscopy. The results show (a) that an inductive effect is operating for the t-butylnaphthalenes, which raises the energies of the lowest unoccupied and of the two highest occupied levels relative to naphthalene and (b) that two opposing effects are operating for the trimethylsilylnaphthalenes, an inductive effect which tends to raise the energy levels, and an electron back donation effect from the aromatic π system to the vacant silicon 3d atomic orbitals which tends to lower the energy levels. This latter effect is the more important for the lowest unoccupied level and the former for the two highest occupied levels.