The structure-directing properties of 2,4,6-trimethylpyridine (TMP) for the formation of colloidal C60-fullerene are revealed in a new paper by Penterman and Liddell Watson.
C60-fullerenes can support singlet excited states that recombine to produce a red photoluminescence and also have a high refractive index and transparency. As such, they have a potential use in colloid-based photonic crystals. Fullerene microcrystals are typically prepared in a solvent-antisolvent system, where the antisolvent promotes nucleation. The solvent-antisolvent ratio, concentration of fullerene, temperature and mixing conditions can be varied to produce particles with different morphologies. However, there are not many compatible solvent-antisolvent combinations, limiting the nature of the particles that can form.
In this paper, the effect of adding TMP to the tetralin or mesitylene:2-propanol solvent-antisolvent system, is investigated. When the solvent is tetralin, TMP plays a dominant role in determining the colloid morphology, monodispersity and crystal structure (an SEM of one fullerene solvate produced is shown below). In the mesitylene system, the crystals have well-defined faceting, higher aspect ratios and improved packing efficiency.
The microcrystals show a reduced fluorescence quantum yield and lifetime, which is thought to be a result of greater fullerene packing efficiency. This is enhanced as the polar TMP additive acts as a blocking agent, adsorbing at the solid–liquid interface and slowing the kinetic rates of growth on certain crystallographic planes. The nucleation period is also shortened, supporting monodispersity.
The use of structure-directing agents could allow the production of fullerene microcrystals with diverse internal crystal structures and external forms. This may allow the development of fullerenes tuned to possess specific properties, including suitability for use as active building blocks for photonic crystals. The authors are continuing to explore the potential of this application.
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