Controlled synthesis of well-defined planar Au nanodendrites with a symmetric single-crystalline structure consisting of trunks and side branches grown along the 211 directions was realized by reducing chloroauric acid in aqueous mixed solutions of dodecyltrimethylammonium bromide (DTAB) and beta-cyclodextrin (beta-CD). It has been revealed that the formation of the supramolecular complexes of DTAB with beta-CD due to host-guest interaction is indispensable for the fabrication of these unique planar Au nanodendrites, and a proper CD-to-DTAB molar ratio is essential to their exclusive formation. A variety of Au nanostructures, such as branched particles consisting of rodlike branches and flowerlike particles consisting of platelike petals, could be readily obtained by simply changing the CD-to-DTAB molar ratio. Moreover, the obtained Au nanodendrites exhibited both a good electrocatalytic activity toward the oxidation of methanol and a good surface-enhanced Raman scattering (SERS) sensitivity for detecting p-aminothiophenol (PATP) molecules, indicating their potential applications including catalysis, biosensing, and nanodevices.

Controlled synthesis of Au nanoparticles with adjustable sizes (10-50 nm) and narrow size distributions (<10% in standard deviation) was realized by reducing hydrochloroauric acid with R-cyclodextrin (R-CD) in an alkaline aqueous solution, which was very simple and "green". It was revealed that a proper pH was essential to the formation of stable dispersions of nonaggregated Au nanoparticles and a higher pH would lead to the welding of the Au nanoparticles into one-dimensional (1D) wires or three-dimensional (3D) aggregates. Moreover, 1D assembly of R-CD-capped Au nanoparticles into nanochains was readily induced by partial removal of the organic stabilization shell, which resulted from the host-guest interactions between R-CDs capped on Au nanoparticle surfaces and toluene molecules. Finally, the as-prepared Au nanoparticles were found to serve as effective catalyst to activate the reduction of 4-nitrophenol in the presence of NaBH 4 , and the application of the assembled Au nanoparticle thin film as a substrate for surface-enhanced Raman scattering (SERS) was also demonstrated.

We report O−H----S hydrogen-bond (Hbond) formation and its excited-state intramolecular H-bond on/off reaction unveiled by room-temperature phosphorescence (RTP). In this seminal work, this phenomenon is demonstrated with 7-hydroxy-2,2-dimethyl-2,3-dihydro-1Hindene-1-thione (DM-7HIT), which possesses a strong polar (hydroxy)-dispersive (thione) type H-bond. Upon excitation, DM-7HIT exhibits anomalous dual RTP with maxima at 550 and 685 nm. This study found that the lowest lying excited state (S 1 ) of DM-7HIT is a sulfur nonbonding (n) to π* transition, which undergoes O−H bond flipping from S 1 (nπ*) to the non-H-bonded S′ 1 (nπ*) state, followed by intersystem crossing and internal conversion to populate the T′ 1 (nπ*) state. Fast H-bond on/off switching then takes place between T′ 1 (nπ*) and T 1 (nπ*), forming a pre-equilibrium that affords both the T′ 1 (nπ*, 685 nm) and T 1 (nπ*, 550 nm) RTP. The generality of the sulfur H-bond on/off switching mechanism, dubbed a molecule wiper, was rigorously evaluated with a variety of other H-bonded thiones, and these results open a new chapter in the chemistry of hydrogen bonds.