Luminescent Calix[4]arene-Based
Metallogel Formed
at Different Solvent Composition
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Abstract
We
have synthesized a calix[4]arene derivative (<b>1</b>)
containing terpyridine and showed that gelation occurred in the presence
of Pt<sup>2+</sup> in DMSO/H<sub>2</sub>O 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/H<sub>2</sub>O ratio
of the solvent. We examined the effects of concentration, temperature,
and time resolution on the luminescence emission of both the gel <b>1</b>-Pt<sup>2+</sup> and the sol <b>1</b>-Pt<sup>2+</sup>. 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<sup>2+</sup> were independent of the concentration of Pt<sup>2+</sup> applied