Entropy-Controlled 2D Supramolecular Structures of <i>N</i>,<i>N</i>′-Bis(<i>n</i>-alkyl)naphthalenediimides on a HOPG Surface

The two-dimensional supramolecular structures of a series of <i>N</i>,<i>N</i>′-bis(<i>n</i>-alkyl)naphthalenediimides (NDIs), whose chain lengths span from C3 to C18, at a liquid–HOPG surface interface, studied by STM and FM-AFM, are assigned with the help of molecular dynamics/molecular mechanics calculations to demonstrate that the C3- and C4-NDIs show lamellar structures, the C4- to C12-NDIs show honeycomb (KAGOME) structures, and the C14- to C18-NDIs show lamellar structures again. The change in supramolecular structure depending on chain length can be explained semiquantitatively by the balance of entropy and enthalpy terms to show the importance of “self-avoiding walk” of the alkyl chain in entropy terms

Simultaneous Imaging of an Enantiomer Pair by Electron Paramagnetic Resonance Using Isotopic Nitrogen Labeling

This Article describes the simultaneous imaging of chiral nitroxyl radicals using electron paramagnetic resonance (EPR). Chiral nitroxyl radicals could be simultaneously visualized with the labeling of isotopic nitrogen. Chiral nitroxyl radicals, hydroxylmethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, were visualized using the method of simultaneous EPR imaging, which refers to the visualization of two kinds of molecules with unpaired electrons in a single image scan. EPR spectra of a racemic mixture of chiral nitroxyl radicals and those of the respective <i>R</i> and <i>S</i> configurations confirmed labeling by isotopic nitrogen. ¹H nuclear magnetic resonance (NMR) imaging and simultaneous imaging of solutions of chiral nitroxyl radicals were performed. The advantages and limitations of simultaneous imaging using EPR are also discussed. Simultaneous imaging with chiral-labeled nitroxyl radicals is a new application of EPR imaging and may be useful for biological studies involving biologically active chiral molecules

Siloxy Group-Induced Highly Efficient Room Temperature Phosphorescence with Long Lifetime

The design and development of organic phosphors that exhibit efficient emission at room temperature but do not contain precious metals such as iridium and platinum have attracted increasing attention. We report herein highly efficient green phosphorescence-emitting 1,4-dibenzoyl-2,5-bis­(siloxy)­benzene crystals in air at room temperature. Remarkable luminescence quantum yields of 0.46 to 0.64 and long lifetimes ranging from 76.0 to 98.3 ms were observed. X-ray diffraction analysis of the single crystals revealed that there were several intermolecular interactions causing suppression of intramolecular motion, thereby minimizing nonradiative decay of the triplet excited state. Comparison with the corresponding 2,5-bis­(dimethylphenylsilylmethyl) and 2,5-bis­(trimethylsilyl) derivatives revealed that the siloxy groups are essential for efficient room temperature phosphorescence. Density functional calculations suggested that σ–n conjugation was operative in the siloxy moieties. Electron spin resonance measurement indicated that the radiative process included generation of the triplet diradical species, whose electron distribution was very similar to that of naphthalene. The present study largely expands the possibilities for the molecular design of precious metal- and halogen-free organic phosphors exhibiting efficient room temperature phosphorescence

Metallic Lustrous Porphyrin Foil with an Exceptional Refractive Index

Metal-lustrous porphyrin foils, self-standing films of fully π-conjugated polymers composed of a glassy porphyrin unit bearing the elastic 3,4,5-tri((S)-dihydrocitronellyloxy)phenyl groups, are disclosed. A remarkable refractive index of 3.04 due to the anomalous dispersion effect of the intense resonance absorption was found for the porphyrin foil of a polymer with a meso-to-meso 1,4-diethynylphenylene-linked backbone (1). Due to the anomalous dispersion effect, the sharp contrast between the intense absorption and specular reflection at the smooth glassy porphyrin foils provides a brilliant noniridescent green metallic luster. On the other hand, the porphyrin foil of a 1,4-diethynyl-2,3,5,6-tetrafluorophenylene-linked polymer with a conformation-locked conjugated backbone via the C–F···H–C interaction between and the edge-faced porphyrin β-protons (2) results in an insignificant refractive index presumably because of the low dielectric constant of fluorine. Nevertheless, the enlarged π-conjugated domain of 2 forms a stable ground-state biradical, while the open-shell character of 1 is moderate. The study reveals that brilliant metallic luster manifests the considerably delocalized π-system in a relatively bulk and/or macroscopic context rather than the molecular-scale properties