A new one-step synthesis of formylated poly [methyl(phenyl)silanediyl] (PMPSi) is reported. The aldehyde groups were incorporated into the parent polymer by the reaction with dichloromethyl methyl ether in the presence of Lewis acid (SnCl4). The reaction takes place via an unstable aryl(methoxy)methyl chloride intermediate. The new procedure is an important simplification of the known four-step synthesis of the poly [(formylphenyl)methylsilanediyl] via chloromethylation in the first step. The presence and reactivity of aldehyde groups in the polymer were proved by means of H-1 NMR, UV-vis, and FT IR spectroscopies. The reduction in relative molecular weight of the parent polysilane after reaction was not so pronounced as in the multistep synthesis. Model compounds N-benzylidene-1-aminopyrene, N-benzylidene-4-phenylaniline, and N-benzylidene-4-phenylazoaniline were synthesized for spectral characterization of the substituted polysilanes. The pi-conjugated systems (pyrene, biphenyl, azobenzene) were attached to the sigma-conjugated polysilane backbone. Photophysical properties, photostability, charge photogeneration, and photoluminescence of these materials were studied. Single- and double-layer light-emitting devices (LEDs) with emission in visible spectral region were fabricated. Their spectral and electrical characteristics were studied. Electroluminescence efficiency in double-layer LEDs reached the value of 0.03-0.06% and was more than 1 order of magnitude higher than that in single-layer devices (similar to0.005%). Modified polysilanes exhibited better photostability than PMPSi and are particularly intended for the use in multilayer or blend devices.