Polymethylphenylsilane (PMPS), prototype of polysilanes, is considered as photoaligning material for liquid crystals (LC). The LC photoalignment on PMPS is characterized by the singular low exposure energy (E less than or equal to 50 mJ) necessary to produce LC alignment. Dependence of the azimuthal anchoring energy W-a an the exposure time tau(exp) is non-monotonous; curve W(tau(exp)) sharply increases, goes through a maximum and decreases to the values close to zero. The easy axis of LC alignment is induced in the direction of light polarization. Possible microscopic mechanisms of LC photoalignment on PMPS layers are discussed.