Photochemical dissociation of p-nitrobenzyl 9,10-dimethoxyanthracene-2-sulfonate films and selective polycation adsorption following irradiation

The effects of 397 nm laser irradiation of spin-coated films of the photoacid generator, p-nitrobenzyl 9,10-dimethoxyanthracene-2-sulfonate (NBAS), have been studied by X-ray photoelectron and Fourier transform infrared spectroscopies (XPS and FTIR). With the exception of a broadening of the C 1s peak, irradiation in vacuum does not lead to significant changes in the XPS spectra. Thin layer chromatography of a dissolved irradiated film shows that at least five photodissociation products are formed, identical to those from an irradiated degassed NBAS solution. Previous solution photochemistry studies identified several decomposition products, including 9,10-dimethoxyanthracene-2-sulfonic acid. XPS and FTIR results are consistent with those products, except that a previously undetected ketone-containing photodissociation product has been identified. Exposure of NBAS films to oxygen, in the absence of light, has been found to cause dramatic changes in the N 1s XPS spectrum; this reaction is accelerated by 397 nm light. XPS has also been used to study the adsorption of poly(diallyldimethylammonium chloride), a cationic polyelectrolyte, on NBAS films as a function of pH. Significantly greater adsorption occurs on irradiated NBAS films compared to unirradiated ones. This may have implications for patterning polyelectrolyte adsorption with light