The low-temperature fluorescence and excitation spectra (T=5-150K) are investigated for the silicon-organic photoconductors poly(di-n-hexylsilane) (PDHS) and poly(methylphenylsilane) (PMPS) embedded in pores of the mesoporous materials MSM-41 and SBA-15, with pore diameters of 2.8 and 5.8 nm, respectively. It is found that the fluorescence spectra of the polymer nanostructures depend on the pore size and are substantially different from the spectra of films. New bands in the visible region, with maxima at 410 nm for PDHS and at 460 nm for PMPS, are observed for the first time in the fluorescence spectra of the 2.8 nm nantostructures. It is assumed that the new bands in the fluorescence spectrum are due to the formation of defect states as a result of a substantial change in the conformation of the polymer chains near the surface of the pores. The change in symmetry of the polymer chains near such defects gives rise to a new band with maximum at 300 nm in the excitation spectrum of PDHS. The defect nature of the new fluorescence bands is confirmed by temperature studies and also by the vanishing of these bands when the pore size is increased to 5.8 nm.