The structure and luminescence properties of europium(iii) triflate doped self-assembled pyromellitamide gels

Abstract

Addition or doping of anion-sensitive self-assembled gels formed from tetrahexyl pyromellitamide 1 in cyclohexane with a few equivalents of europium(III) triflates results in materials with red luminescence arising from the europium(III) ions. Gelation and spectroscopic studies suggest that the europium(III) ions bind to the amides in 1 with an apparent association constant of 770 M⁻¹. Luminescence lifetime studies show a 273 ± 8 μs lifetime for the ⁵D₀ → ⁷F₂ transition upon excitation with laser light at 300 nm. Interestingly, the red europium emission can also be observed using a multi-photon microscope and a near infrared (NIR) excitation source of 780 nm but this is almost certainly a quadratic electro-optic effect (Kerr effect) due to the intense laser beam generating a white light continuum excitation into the ultraviolet range. These results do demonstrate that self-assembled gels can be doped with europium salts generating smart soft material for applications in time-gated spectroscopy and microscopy.