Abstract The first vertical π-ionization energies of substituted furans as determined by photoelectron spectroscopy are compared with the results of CNDO/2 calculations. The analysis of the photoelectron spectra and quantum chemical calculations for furylsilanes, difurylsilanes and some carbon analogs has shown the importance of the p π-d π interaction as well as of the conjugation and necessity of the inclusion of silicon d-atomic orbitals into ...