Ordering minimalist bridged polysilsesquioxane films under visible LED light irradiation

A visible light-mediated sol–gel process can promote the ordering of hexylene, octylene, and decylene-bridged polysilsesquioxane (SQ) with very simple organosilane building blocks having only a short alkylene bridging group: (CH3O)3SiCnH2nSi(OCH3)3 (n = 6, 8, 10). Photocondensation and self-assembly of films are promoted through exposure to a light-emitting diode (LED; 405 nm). The solvent-free synthesis involves very low light intensity (0.1 mW/cm2) and a minimum amount of photoacid generator (PAG; 0.5 wt%) acting as a photocatalyst. X-ray diffraction (XRD) and scanning electron microscopy (SEM) prove the high level of organization, while real-time Fourier transform infrared spectroscopy shows conformational ordering of alkylene chains throughout irradiation. Molecular modeling reveals a multilayer structure based on the stacking of a single polysiloxane chain, with organic groups attached to adjacent Si atoms showing up and down orientation.