Laser photolysis of pyrenesulfonate and pyrenetetrasulfonate via two-photon ionization in aqueous and reverse micellar solutions

We investigated the laser photolysis of tetrasodium 1,3,6,8-pyrene-tetrasulfonate (Na4PS4) and sodium 1-pyrenesulfonate (NaPS) in aqueous and reverse micellar solutions. The photoproducts as well as their yields were found to strongly depend on the reaction parameters such as pH, dissolved gases and the size of water pool. The primary reaction in aqueous solution was commonly presented by laser-induced formation of the cation radicals followed by hydroxylation of them. In the case of PS44−, pyranine was efficiently and highly selectively formed, possibly via desulfonation of the cation radical, P+S44−, followed by the hydroxylation. On the other hand, from PS−, hydroxypyrenesulfonate (PSOH) was initially formed in alkaline solution and desulfonation occurred secondarily, leading to the formation of hydoxypyrene. These photoreactions were markedly suppressed within a small water pool of the reverse micelle. As the size of water pool increased similar photochemical reactions occurred depending on the dissolved gases. The observed micellar effects could be explained based on the pH of water pool and the nature of the cation radicals in it.