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The origin of white photoluminescence in polysilanes has long been disputed, and this emission is closely connected with information recording in nanotechnologies. We elucidated UV degradation of an archetypal model polymer poly[methyl(phenyl)silane] by using a new method for electronic structure mapping of organic semiconductors, energy-resolved electrochemical impedance spectroscopy (ER-EIS) and photoluminescence spectroscopy. UV exposure at 345 nm resulted in two defect bands above the highest occupied molecular orbital (HOMO) in the energy region from −5.5 eV to −3.5 eV with respect to the zero vacuum energy level. The respective density of states was 1016 − 1017 cm−3eV−1, and the total integrated concentration was 0 − 1017 cm−3. The photoluminescence in the long-wavelength region gave wide bands with photon energies from 2.2 eV to 3.2 eV (corresponding to wavelengths from 600 nm to 390 nm). The observed bands were interpreted by assuming the formation of energetically distributed Si branching radiative states, whose distribution in the HOMO − lowest unoccupied molecular orbital (LUMO) gap was observed by using ER-EIS. The quantum efficiency of defect state formation increased from (x)345 nm = 0.0045 to (x)290 nm = 0.053. The obtained results may contribute to the production of effective polysilane nanomasks and to information recording.