Synthesis and Properties of [7]Helicene-like Compounds Fused with a Fluorene Unit

[7]­Helicene-like compounds with a fluorene unit were successfully synthesized using a platinum-catalyzed double cyclization reaction. Crystal structures and photophysical properties of these compounds were also studied. In particular, they were found to exhibit a high fluorescence quantum yield and a relatively large <i>g</i> value (dissymmetric factor) of circularly polarized luminescence (CPL) for small molecules

Time-Resolved Observation of Chiral-Index-Selective Wrapping on Single-Walled Carbon Nanotube with Non-Aromatic Polysilane

In the present paper, we ascertain two novel findings on chiral-index-selective binding/separating of single-walled carbon nanotubes (SWNTs) with a nonaromatic polymer, poly­(dialkylsilane) (PSi). PSi is a typical σ-conjugated polymer, composed of alkyl side chains attached to the silicon (Si)-catenated main chain. First, PSi’s with linear alkyl side chains showed significant diameter-selective wrapping for SWNTs with ca. 0.9 nm in diameter, resulting in the selective separation of (7,6) and (9,4) SWNTs. Its driving force was demonstrated to be cooperative CH−π interactions among the alkyl side chains of PSi’s and the curved graphene of SWNTs. Second, the dynamic wrapping behavior of PSi’s onto SWNTs was elucidated with time-resolved UV spectroscopy. Highly anisotropic UV absorption of PSi along the Si main chain was utilized as a “chromophoric indicator” to monitor the global/local conformations, which enabled us to track kinetic structural changes of PSi’s on SWNTs. Consequently, we concluded that upon wrapping, flexible/helical PSi with an average dihedral angle (φ) of 145° and Kuhn’s segment length (λ^–1) of 2.6 nm interconverted to the more stiffer/planar conformation with 170° and λ^–1 of 7.4 nm. Furthermore, through kinetic analyses of the time-course UV spectra, we discovered the fact that PSi’s involve three distinct structural changes during wrapping. That is, (i) the very fast adsorption of several segments within dead time of mixing (<30 ms), following (ii) the gradual adsorption of loosely wrapped segments with the half-maximum values (τ₁) of 31.4 ms, and (iii) the slow rearrangement of the entire chains with τ₂ of 123.1 ms, coupling with elongation of the segment lengths. The present results may be useful for rational design of polymers toward chiral-index-selective binding/separating of desired (<i>n</i>,<i>m</i>) SWNTs

[70]Fullerenes Assist the Formation of Phospholipid Bicelles at Low Lipid Concentrations

The incorporation of neutral [70]­fullerenes (C₇₀) led to bicelle formation in a relatively low lipid concentration range from neutral lipid mixtures (DMPC/DHPC). Furthermore, C₇₀ addition resulted in the formation of large bicelles with a radius of ca. 100 nm, in contrast to C₇₀-free bicelles that were formed from anionic lipid mixtures (DMPC/DHPC/DMPG). The stabilization of these bicelles was attributed to C₇₀ incorporation into the membranes

Facile Synthetic Route to Highly Luminescent Sila[7]helicene

A facile synthetic route to dimethylsila[7]helicene by using a Lewis acid catalyzed double-cyclization reaction for construction of the twisted two phenanthrene moieties is described. Sila[7]helicene exhibited a high fluorescence quantum yield and a realatively large <i>g</i> value (dissymmetric factor) of circularly polarized luminencence (CPL) for small molecules

Facile Synthetic Route to Highly Luminescent Sila[7]helicene

A facile synthetic route to dimethylsila[7]helicene by using a Lewis acid catalyzed double-cyclization reaction for construction of the twisted two phenanthrene moieties is described. Sila[7]helicene exhibited a high fluorescence quantum yield and a realatively large <i>g</i> value (dissymmetric factor) of circularly polarized luminencence (CPL) for small molecules