Luminescent calix[4]arene-based metallogel formed at different solvent composition.

ABSTRACT

We have synthesized a calix[4]arene derivative (1) containing terpyridine and showed that gelation occurred in the presence of Pt(2+) in DMSO/H2O of varying compositions. Gelation was presumably mediated by the Pt-Pt and π-π stacking interactions. The scanning electron microscopy image of the xerogel showed a spherical structure with diameter of 1.8-2.1 µm. Interestingly, the metallogel showed strong luminescence enhancement, which was dependent on the DMSO/H2O ratio of the solvent. We examined the effects of concentration, temperature, and time resolution on the luminescence emission of both the gel 1-Pt(2+) and the sol 1-Pt(2+). The luminescence lifetimes of the metallogel were particularly long, on the order of several microseconds. The luminescence lifetimes were also strongly dependent on the solvent composition. We also determined the thermodynamic parameters for the self-assembly of the gel by the Birks kinetic scheme. Furthermore, the rheological properties of the metallogels in the presence of more than 4.0 equiv of Pt(2+) were independent of the concentration of Pt(2+) applied.