Direct and Sensitized Photolysis of Dispersed Photoacid Generators

Abstract

This work proposes water-borne photopolymers cast and developed solely with neutral water by incorporating mechanically milled sub-micron particles of poorly water-soluble photoacid generators (PAGs) to make a poly(vinyl alcohol) film insoluble in water with aid of an acid-sensitive crosslinker. Fluorescence measurements of milled mixtures of anthracene and a tiny amount of tetracene in water revealed that the solid-state energy transfer occurs through singlet exciton migration as a result of mechanochemical crystal mixing. Solid-state electron transfer was also verified by fluorescence quenching of milled mixtures of PAG and emissive sensitizers including anthracene derivatives as a consequence of exciton diffusion in sensitizer crystals to reach at the particle surface to transfer an electron to PAG solid. Factors affecting solid-state electron transfer efficiency include the nature of PAG and sensitizers, particle sizes and exciton diffusion length, whereas bis[p-(tert-butylphenyl)]iodonium hexafluorophosphate (1a) was the best solid-state quencher. Solid-state sensitized photoacid generation was confirmed by irradiating aqueous dispersions of co-milled PAG and a sensitizer. Based on these results, three-component photopolymers comprised of an aqueous dispersion of PAG in absence or in the presence of a co-milled sensitizer, poly(vinyl alcohol) and a water-soluble diepoxy were prepared to exhibit photosensitivity of 17 mJ cm-2 by the direct photolysis of a dispersed sulfonium salt and that of ca.120 mJ cm-2 by the photolysis of 1a sensitized with co-milled 9, 10-dipropoxyanthracene.