Illuminating disorder: Many highly efficient light emitters are members of the family β‐NaLnF4 (Ln=Y, La–Lu). Diffuse X‐ray scattering is combined with single‐crystal absorption spectroscopy at cryogenic temperatures to unambiguously identify and characterize two crystallographically inequivalent spectroscopic sites (A and B). The high light yield is correlated with the existence and nature of these sites.
If quantum interference patterns in the hearts of polycyclic aromatic hydrocarbons could be isolated and manipulated, then a significant step toward realizing the potential of single-molecule electronics would be achieved. Here we demonstrate experimentally and theoretically that a simple, parameter-free, analytic theory of interference patterns evaluated at the mid-point of the HOMO-LUMO gap (referred to as M-functions) correctly predicts conductance ratios of molecules with pyrene, naphthalene, anthracene, anthanthrene, or azulene hearts. M-functions provide new design strategies for identifying molecules with phase-coherent logic functions and enhancing the sensitivity of molecular-scale interferometers.
In recent years, microsource sealed tubes in combination with multilayer optics have been adopted in many crystallography laboratories for very low power X‐ray generation, monochromatization and high‐brilliance microfocusing. All these factors allow high‐performance experiments on a laboratory scale. However, a fundamental defect of this technology has been discovered, namely a significant contamination of the characteristic radiation by low‐energy photons. Some simple experiments are reported, showing that the contamination can significantly reduce the accuracy of the measured intensities, especially when Mo Kα radiation is used. A simple and economic solution to the problem is proposed: an aluminium filter approximately 100 µm thick, which efficiently removes the low‐energy contaminant photons.
An efficient synthetic approach to construct a fully substituted benzo[1,2-b:4,5-b']difuran (BDF) 2a via base-catalyzed double annulations is presented. Compound 2a can readily undergo Suzuki, Heck, and Sonogashira coupling reactions to afford in good yields a manifold of extended pi-conjugated BDF derivatives, e.g., with pyridine termini (4-6) and with different spacers. These are highly luminescent materials that undergo two reversible one-electron oxidations. Remarkably, their photophysical and electrochemical properties can be largely tuned by methylation or protonation. Consequently, they can function as pH-dependent fluorescence switches. Finally, the observed electronic properties are explained on the basis of density functional theory.
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