Statistical aging and nonergodicity in the fluorescence of single nanocrystals

The relation between single particle and ensemble measurements is addressed for semiconductor CdSe nanocrystals. We record their fluorescence at the single molecule level and analyze their emission intermittency, which is governed by unusual random processes known as Lévy statistics. We report the observation of statistical aging and ergodicity breaking, both related to the occurrence of Lévy statistics. Our results show that the behavior of ensemble quantities, such as the total fluorescence of an ensemble of nanocrystals, can differ from the time-averaged individual quantities, and must be interpreted with care.     

Noise-reduction capabilities of a raman-mediated wavelength converter

We describe ultrawideband Raman-mediated wavelength conversion. The nonlinear conversion transfer function is calculated analytically and simulated numerically in the cw regime, and the predicted performance is confirmed experimentally. Data conversion from long- to short-wavelength bands with signal reshaping and significant noise reduction are demonstrated experimentally at 10 Gbits/s and modeled by numerical simulations. Q factors and extinction ratios that are both larger than 10 dB are possible over an effective conversion bandwidth of 35 nm.     

Time-gated biological imaging by use of colloidal quantum dots

The long (but not too long) fluorescence lifetime of CdSe semiconductor quantum dots was exploited to enhance fluorescence biological imaging contrast and sensitivity by time-gated detection. Significant and selective reduction of the autofluorescence contribution to the overall image was achieved, and enhancement of the signal-to-background ratio by more than an order of magnitude was demonstrated.     

Phenanthroline-derived ratiometric chemosensor for ureas

The syntheses of 1,10-phenanthroline fluorophore-based chemosensor 7 and its truncated analog 9 are reported. Interactions of these compounds with urea, thiourea, 1,3-dimethylurea, tetrahydropyrimidin-2(1H)-one, imidazolidin-2-one, and selected uronium salts were assessed by three-dimensional excitation-emission spectroscopy, UV-vis absorbance, and fluorescence titrations. Chemosensor 7 was found to be capable of distinguishing between neutral ureas and their salts, by producing a different optical response for each type of compounds. The complexation of urea by 7 was also studied by selective-NOE 1H NMR, 13C NMR (using 13C-labeled guest), and MALDI-TOF mass spectrometry. In addition, we performed DFT calculations (B3LYP 3-21g** level) for structures of complexes of 7 with urea, imidazolidin-2-one, and tetrahydropyrimidin-2(1H)-one. Development of chemosensor 7-type compounds in conjunction with differential excitation-emission spectroscopy represents an important step toward the development of novel tools for ureas and their salts analysis.     

A triangular macrocycle altering planar and bulky sections in its molecular backbone

A triangular macrocyclic molecule has been synthesized which consists of substituted phenanthrene vertices interconnected by 1,3-diethynylbicyclo[1.1.1]pentane sides. The molecule is the very first example of exploiting the bicyclopentane motif in the construction of a shape persistent macrocycle's backbone. It carries new features such as bulkiness, nonconjugated σ-bonding, and a certain conformational flexibility due to its easy longitudinal rotation. We have used some of the features in order to rationalize the observed tendency of the compound to form films on various surfaces.