Excited state vs. photoinduced charge separation in bundles of a polyamide containing pendant AlIII phthalocyaninetetrasulfonate groups. Potential applications to photocatalysis

A new polyimide containing pendant AlIIIphthalocyaninetetrasulfonate groups, [HOAlIII(pc)(SO3−)3(SO2N<)]\3, was synthesized and the morphology of the polymer, poly(HOAlIIItspc), in aqueous solutions was investigated using transmission electron microscopy and UV–vis absorption and emission spectroscopies. The strands of poly(HOAlIIItspc) are associated in near spherical bundles with ∼150 nm diameter in aqueous solutions. Most of the pendants in the bundles are forming π-stacks where the largest fraction of them must be dimers. Flash photochemical observations in a 0.15 ps to 100 μs time domain revealed the photogeneration of pendant radicals, pendant2− and pendant4−. This process stands in contrast with the photochemistry that tetrasulfonated AlIII phthalocyanine shows under the same experimental conditions of poly(HOAlIIItspc). The kinetics of the phthalocyanine radicals formation and disappearance is consistent with energy and charge transfers between phthalocyanine pendants in the bundle. Radical scavengers (methylviologen, O2, cathecol, lignine) present in the solutions of poly(HOAlIIItspc) trapped the phthalocyanine radicals demonstrating that scavenging reactions can compete with the slow radical–radical annihilation process and used for the photocatalysis of redox processes.