Abstract Radical cation salts of 2,2′,6,6′-tetra(methyl and aryl)-4,4′-biselenopyranylidenes, are prepared by direct iodine oxidation. Several polyiodide salts are isolated (from each donor), the stoichiometries of which are a function of molecular ratio of the reagents. The salts are investigated by optical absorption spectroscopy (between 0.025 and 4.94 eV) and conductivity measurement determined on compressed pellets at room temperature. Optical spectra show peculiar absorption peaks: above 1 eV, intramolecular and isovalent transition peaks and between 0.25 and 0.99 eV, for the complexes with low iodine stoichiometry, and intervalence charge-transfer transition band relative to a transition between neutral donor and radical-cation. This band is characteristic of a mixed valence state. The degree of charge-transfer increases when the iodine stoichiometry increases for a given substituent with a subsequent decrease of the electrical conductivity attributed to an augmentation of the Coulomb's repulsions. Three mixed-valence polyiodides salts of the 2,2′,6,6′-tetraphenyl-4,4′-biselenopyranylidine: (1:2), (1:3.5) and (1:5.9), have been characterized further. The resonance Raman spectra display two kinds of iodine species, I − 3 and I − 5, in the 1:3.5 and 1:5.9 salts. The structure of the 1:2 salt has been investigated by X-ray diffraction. A compact, regular and segregated structure of the donor molecules along the axis is identified. The donor stacks delimit channels filled with linear polyiodide chains. This confirms the observed stoichiometry and results in a charge-transfer of 0.67 electron per donor for the 1:2 salt (2b-(I- 3)0,67). The (1:3.5) complex has a semiconducting behavior from 115 to 255 K and a single-crystal electrical conductivity of 4 S.cm−1 at room temperature. This semiconducting state and that of the 1:5.9 salt are derived from the reflectance spectra (performed on polycrystalline compaction) between 0.12 and 1.23 eV where the reflectivity decreases towards the infrared. On the contrary, the 1:2 salt shows a reflectance value about 25% from the infra-red (0.12 eV) to the Drude edge (0.41 eV) consistent with a quasione dimensional metallic character. The Drude's model affords an optical conductivity of 541 S.cm−1. This metallic state is also revealed in a weak variation of the 1:2 salt static paramagnetic susceptibility with temperature. This temperature dependence increases with iodine content and matches a Curie-Weiss behaviour for the 1:5.9 salt, whose stoichiometry deduced from the susceptibility study is (2b-(I- 3)0,67).