We report photoemission spectra of the valence region for a series of linearly benzo-annelated porphyrazine molecules in thin films. This family of compounds, with stepwise varied ligand size, is an ideal model system to investigate the evolution of the electronic structure with the increasing pi-electron system of the molecule. Specifically, the electronic structure of tert-butyl-substituted metal-free tetraazaporphyrin, phthalocyanine, and naphthalocyanine is investigated by photoelectron spectroscopy using synchrotron radiation in the 70-105 eV photon energy range. A shift of the highest occupied molecular orbital toward lower binding energies as a function of the increasing ligand size is found and discussed on the basis of existing theoretical calculation. Only a small influence of the tert-butyl substituent group on the photoemission spectra is observed as compared to spectra of unsubstituted molecules.