Photoexcitation, photodegradation and metastability of electronic states of poly[methyl(phenyl)silylene] on air and in vacuo are discussed. UV radiation causes the formation of excitons, ion-pairs, free radicals, delocalized positive polarons and scission of Si-Si bonds. Due to the chain deformation during the exciton and polaron formation metastable electronic states 0.45 eV deep originate in vacuo. These states make the conjugation length shorter and can be thermally annealed. On air polysiloxane structures arise.