Intercalation and photophysical characterization of 1-pyrenemethylamine in zirconium phosphate layered materials

The ion exchange of the luminescent probe 1-pyrenemethylamine (PYMA) into zirconium phosphate (ZrP) layered materials has been accomplished. The matrices used were the hexahydrated 10.3 A phase of ZrP (10.3 A ZrP, where 10.3 A represents the interlayer distance) and butylammonium-exchanged ZrP (BAZrP) with an expanded 18.6 A interlayer distance. The XRPD patterns for the 10.3 A ZrP after PYMA exchange (PYMA-exchanged ZrP), at high PYMA concentrations, show an increase in the interlayer distance from 10.3 A in unexchanged 10.3 A ZrP to 23.5 A in PYMA-exchanged ZrP, indicating PYMA intercalation. The luminescence spectrum for the PYMA-exchanged ZrP exhibits an excimer band at 458 nm that is absent in the luminescence spectrum of PYMA in aqueous solution at low concentrations. The intensity of the excimer emission increased at low PYMA concentrations. These results are in contrast to experiments using the BAZrP matrix. The XRPD patterns for PYMA-exchanged BAZrP do not show changes in the interlayer distance, which suggests that PYMA is not being intercalated and is only surface bound. The luminescence spectrum for PYMA-exchanged BAZrP exhibits a lower emission intensity in its excimer band, at different PYMA concentrations, compared with the PYMA-exchanged ZrP excimer band. For PYMA-exchanged ZrP, we propose a process in which exchange at low PYMA concentrations occurs at external surface sites with clustering promoting excimer formation followed by exchange at high PYMA concentrations occurring at interior sites reducing excimer formation.