An efficient method for the surface functionalization of luminescent quantum dots with lipoic acid-based ligands

We describe an operationally advantageous general methodology to efficiently activate lipoic acid-based compounds - a family of popular surface ligands for semiconductor nanocrystals - by the use of a borohydride exchange resin, and the use of the activated species to replace the native surface ligands of quantum dots. The procedure enables the phase transfer of the nanocrystals between polar and aqueous media and, if unsubstituted lipoic acid is used, a facile adjustment of their solubility in a wide range of solvents with varying polarity (from hexane to water). We show that the protocol is applicable to different types of nanocrystals and a variety of lipoic acid-based ligands, and that the resulting quantum dots maintain their optical properties - in particular, an intense luminescence - and long term colloidal stability

Reversible Photocapture of a [2]Rotaxane Harnessing a Barbiturate Template

Photoirradiation of a hydrogen-bonded molecular complex comprising acyclic components, namely, a stoppered thread (<b>1</b>) with a central barbiturate motif and an optimized doubly anthracene-terminated acyclic Hamilton-like receptor (<b>2b</b>), leads to an interlocked architecture, which was isolated and fully characterized. The sole isolated interlocked photoproduct (Φ = 0.06) is a [2]­rotaxane, with the dimerized anthracenes assuming a head-to-tail geometry, as evidenced by NMR spectroscopy and consistent with molecular modeling (PM6). A different behavior was observed on irradiating homologous molecular complexes <b>1</b>⊂<b>2a</b>, <b>1</b>⊂<b>2b</b>, and <b>1</b>⊂<b>2c</b>, where the spacers of <b>2a</b>, <b>2b</b>, and <b>2c</b> incorporated 3, 6, and 9 methylene units, respectively. While no evidence of interlocked structure formation was observed following irradiation of <b>1</b>⊂<b>2a</b>, a kinetically labile rotaxane was obtained on irradiating the complex <b>1</b>⊂<b>2c</b>, and ring slippage was revealed. A more stable [2]­rotaxane was formed on irradiating <b>1</b>⊂<b>2b</b>, whose capture is found to be fully reversible upon heating, thereby resetting the system, with some fatigue (38%) after four irradiation–thermal reversion cycles

Modulation of the solubility of luminescent semiconductor nanocrystals through facile surface functionalization

The solubility of luminescent quantum dots in solvents from hexane to water can be finely tuned by the choice of the countercations associated with carboxylate residues present on the nanocrystal surface. The resulting nanocrystals exhibit long term colloidal and chemical stability and maintain their photophysical properties. This journal is © the Partner Organisations 2014