Photoinduced self-assembly of carboxylic acid-terminated lamellar silsesquioxane: highly functional films for attaching and patterning amino-based ligands

Recently, long n-alkyltrimethoxysilanes (H3C(CH2)nSi(OCH3)3) have proven to self-assemble into mesoscopically ordered passive lamellar films through an efficient solvent-free photoacid-catalysed sol–gel process. By using an analogue precursor architecture presenting a terminal ester group (H3COC(O)(CH2)10Si(OCH3)3), both functional and tuneable nanostructured organosilica films were synthesized, while keeping all the processing advantages of light-induced self-assembly. The subsequent attachment of a fluorescent amino-based ligand (Safranin O) was performed using a two-step procedure. The ester end groups were first hydrolysed in reactive carboxylic acid using standard methods, and activated with an amino ligand to form amide bonds. Hydrolysis and ligand coupling were assessed through infrared and solid-state 1H NMR spectroscopy. Direct patterning of the fluorescent ligand-functionalized silsesquioxane film was performed by exposure to deep UV light under a mask to cause the local degradation of the dye. The resultant photopatterned film was detected using fluorescence microscopy. This UV method could represent an effective and general approach for attaching and patterning amino-based ligands, with less restriction on substrate and surface preparation than self-assembled monolayers.