Yongqian Xu

Aggregation Control of Squaraines and Their Use as Near-Infrared Fluorescent Sensors for Protein

A series of squaraine dyes are found to be in H- or J-aggregates and are almost nonfluorescent in aqueous solution. Upon addition of bovine serum albumin (BSA), however, the fluorescence intensity (at lambda(em) approximately 690 nm) increases by a factor of up to 200. Transformation of the dye molecules from the aggregates to the monomeric species appears to be responsible for the large fluorescence turn-on. While both H- and J-aggregates contribute to the observed fluorescence turn-on, the former appears to play a more important role. Electrophoresis imaging shows that these probes are good BSA indicators.

Formation of linear supramolecular polymers that is based on host-guest assembly in water.

Cucurbit[n]urils (n = 7, 8) and thiazole orange (TO) dyes in aqueous media were found to form host-guest inclusions in different stoichiometries. Supramolecular structures and linear supramolecular polymers were observed through the hydrophobic effect and π-π interactions in aqueous solution.

Highly Selective Dispersion of Carbon Nanotubes by Using Poly(phenyleneethynylene)-Guided Supermolecular Assembly

Isolation of single-walled carbon nanotubes (SWNTs) with specific chirality and diameters is critical for achieving optimum performance of SWNTs in various applications. A water-soluble π-conjugated polymer, poly[(m-phenyleneethynylene)-alt-(p-phenyleneethynylene)], 3, is found to exhibit high selectivity in dispersing SWNT (6,5). The polymers ability to sort out SWNT (6,5) appears to be related to the carbon-carbon triple bond, whose free rotation allows a unique assembly of chromophores in a helical conformation. The observation is consistently supported by fluorescence, Raman, and UV-vis-NIR absorption spectra. The intriguing selectivity of 3 to SWNT (6,5), however, is not observed for the vinylene analogue polymer 1, showing that the carbon-carbon triple bond could play a unique role in sorting out a specific SWNT. The observed selectivity from 3 could be attributed to a combination of the helical cavity size restrain and electronic interaction associated with the local chromophore arrangement. This strategy could be expanded for efficient SWNT sorting when the helical conformation is further finely tuned.