Photolysis of 1-pyrenemethylamine ion-exchanged into a zirconium phosphate framework

The photolysis of the luminescence probe 1-pyremethylamine (PYMA) ion-exchanged into a layered zirconium phosphate (ZrP) framework has been studied. The ZrP used was an hydrated form of α-ZrP with six water molecules per formula unit and with an interlayer distance of 10.3 Å. The luminescence spectrum for a PYMA ion-exchanged in ZrP (PYMA-exchanged ZrP) colloidal suspension in aqueous solution, after irradiation, shows a rapid decrease of the most intense peak at 376 nm and an increase of the peak at 383 nm of the PYMA molecule. The photolysis of a PYMA aqueous solution proceeds slowly to give a luminescence spectrum similar to that observed upon photolysis of PYMA-exchanged ZrP. We have identified pyrene, 1-hydroxypyrene, 1,6-pyrenedione, and 1,8-pyrenedione as stable photoproducts using steady-state luminescence spectroscopy, high performance liquid chromatography, and UV-vis spectrophotometry. The XRPD pattern for PYMA-exchanged ZrP, after photolysis, shows that the photoproducts remain entrapped between the layers. The influence of polarity of the solvent and the presence of air, nitrogen, or oxygen on the formation of the photoproducts have been investigated. Based on the photoproduct identification a reaction mechanism is proposed involving the formation of radicals.