Search

A series of 1,3,5-triphenyl-2-pyrazoline (TPP) nanocrystals were prepared by the reprecipitation method. The electronic transitions of TPP nanocrystals have been studied using both absorption and fluorescence spectra. An absorption feature at about 400 nm gradually appeared with increasing nanocrystal size. This feature resulted from the formation of the charge-transfer (CT) exciton in nanocrystals. It was also supported by the longer decay time of the nanocrystal emission from CT compared with that of the solution emission from [S.sub.1] at 298 K. On the other hand, the different behavior of the molecular [pi]-[pi] * and n-[pi] * transitions originates from the different overlapping modes of the pyrazoline [pi] orbital and n-electron orbital, according to the molecular model calculations. The nanocrystal emission from both the [S.sub.1] and CT states was found at 77 K; moreover, the emission intensity redistributed from [S.sub.1] to CT with increasing nanocrystal size. In contrast, at 298 K, only the emission from the CT states was observed, since the thermal fluctuation easily relaxes the excited electrons into CT states through vibration. Key words: reprecipitation method, organic nanocrystals, charge-transfer exciton, size-dependent property.

Transition-metal oxides — including tungsten oxide, molybdenum oxide, titanium dioxide, vanadium pentoxide, niobium pentoxide and zinc oxide — exhibit photochromism upon bandgap excitation. These oxides constitute an important group of inorganic chromogenic materials, which is of great significance in the perspective of science and technology. During the past several decades, great progresses have been made in the microstructure, photochromic behavior and mechanism of these oxides, specifically of tungsten oxide. These studies underscore the opportunity of using these materials in photonic applications. The details will be presented in this review. [ABSTRACT FROM AUTHOR]

A simple graphene quantum dots (GQDs)-based fluorescence sensing system was developed for rapid, sensitive and low-cost detection of ascorbic acid (AA) in the presence of copper ions. Due to the efficient electron-transfer between GQDs and Cu 2+ ions, the fluorescence of GQDs was greatly quenched by Cu 2+ ions. Upon addition of ascorbic acid, Cu 2+ was reduced to Cu + and the interaction of Cu 2+ -GQDs was destroyed, which inhibit the quenching and thus leading to fluorescence recovery of GQDs. The detection process is ultrafast and can be completed within 5 min. The linear response range of AA was obtained from 0.3 μM to 10 μM. The detection limit was as low as 94 nM, which was comparable to or even better than other reported assays. In addition, this sensing system also showed good selectivity for detecting AA in the presence of different physiological molecules and inorganic ions. Finally, the proposed sensing system was successfully applied to assay AA in real samples with satisfactory results. [ABSTRACT FROM AUTHOR]

The ordered array of nanovoids in nanoporous networks, such as honeycomb, Kagome, and square, provides a molecular template for the accommodation of "guest molecules". Compared with the commonly studied guest molecules featuring high symmetry evenly incorporated into the template, guest molecules featuring lower symmetry are rare to report. Herein, we report the formation of a distinct patterned superlattice of guest molecules by selective trapping of guest molecules into the honeycomb network of trimesic acid (TMA). Two distinct surface patterns have been achieved by the guest inclusion induced adaptive reconstruction of a 2D molecular nanoporous network. The honeycomb networks can synergetically tune the arrangement upon inclusion of the guest molecules with different core size but similar peripherals groups, resulting in a trihexagonal Kagome or triangular patterns.

We have attempted to develop surface-enhanced Raman scattering (SERS) substrates by the use of two-dimensional (2D) Au nanorod arrays and to characterize the SERS-active sites of the Au nanostructures. We prepared two different types of 2D Au nanorod arrays by means of the anodic aluminum oxide (AAO) template-assisted nanofabrication. In the template-embedded array (type I) an Au nanorod fills up the AAO pore, while in the annularly spaced array (type II) an Au nanorod keeps approximately 20 nm away from the pore wall. The strongest SERS effect was observed for both types of substrates with an Au nanorod diameter of approximately 66 nm. With respect to the bare AAO template, the NaOH-etched (unetched) type I substrate with the 66 nm Au nanorod showed 115-fold (63-fold) enhancement in Raman scattering, corresponding to a SERS enhancement factor of 10(7)-10(9). For the unetched and ordered Au naonorod arrays, the SERS-active sites localized around the rod end, whereas for the NaOH-etched and partially aggregated Au nanorods, hot spots for SERS were found in the interstices between rod tips. The type II substrate allowed the effect of rod length on the SERS response to be investigated, and the SERS response was observed to vary very little with the rod length increase (250-1000 nm), indicating that majority of the signal originates at the rod end. A comparison between the analytes all-trans-beta-carotene and pyridine suggests that, for both types of substrates, the electromagnetic enhancement is predominant over the chemical enhancement. This work demonstrates that the unetched type I substrate is highly SERS effective, for which the fabrication protocol is advantageous in its simplicity and reproducibility.

An environmentally benign transparent photochromic film, 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]-naphtho[2,1-b][1,4]oxazine] (SPO) /gamma-cyclodextrin (gamma-CD), was prepared using the cast-coating method, and the nanocavity effect of gamma-CD on the photochromism of SPO was studied. The film mainly consists of the inclusion complex SPO@gamma-CD, which has been verified by EA, TGA, XRD, MS, and ICD to comprise a 1:1 host-guest stoichiometry. The film shows normal photochromism. The decoloration of photomerocyanine (PMC) fits biexponential decay: PMCs located in the cavity of gamma-CD decay with a rate constant of 6.0 x 10(-2) s(-1), which is nearly one order faster than those PMCs outside of the cavity.