A series of oligo-phenylenevinylenes are investigated by spectroscopic measurements and calculations with the aim to rationalize the correlation between the electronic structure of the molecules and their efficiency as two-photon singlet oxygen sensitizers. The band-shape functions of selected two-photon absorption processes are analyzed and the corresponding spectra are deconvoluted. This analysis allows for a comparison between calculated and measured two-photon absorption cross sections where a reasonable agreement is found.