Volume 86, Issue 4

The use of supramolecular interactions for controlling the electronic and photophysical properties of organic π-conjugated materials is described. This leads to materials presenting unique properties, such as light-induced switching of polarization (photopolism), or the spontaneous formation of highly luminescent vesicles. In another approach, reversible covalent bonds are used to prepare densely packed fullerene monolayers whose conductivity could be probed using conducting AFM.

We report the synthesis of a series of novel tetraazaacene derivatives and compare their stability with respect to size, oxidation potential and position of the TIPS-ethynyl groups. The latter has the most pronounced effects on the stability. In case of azatetracenes where TIPS-alkynes are either attached laterally or in the peri -positions, the former ones dimerized while the latter are stable. Attempts to expand this concept to the corresponding tetrakis- peri -substituted heptacenes led to the isolation of the dimerized butterfly product.

The structural chemistry of carbon nanotube molecules has been of increasing interest, as molecular entities with fundamental structures of finite nanotube molecules have emerged. For the new field to be developed further, appropriate structural descriptors are necessary as the basis for discussion. In this paper, we propose new geometric descriptors for finite nanotube molecules. Based on popular existing descriptors, these new descriptors provide geometric measures for length and bond- and atom-filling in tubular molecular structures.

The edge state, which is a peculiar magnetic state in zigzag-edged graphene nanoribbons (ZGNRs) originating from an electron–electron correlation in an edge-localized π-state, has promising applications for magnetic and spintronics devices and has attracted much attention of physicists, chemists, and engineers. For deeper understanding of the edge state, precise fabrication of edge structures in ZGNRs has been highly demanded. We focus on anthenes, which are peri -condensed anthracenes that have zigzag and armchair edges on the molecular periphery, as model systems for understanding, and indeed prepare and characterize them. This paper summarizes our recent studies on the origin of the edge state by investigating anthenes in terms of the relationship between the molecular structure and spin-localizing character.

Electron-donating 1,1,4,4-tetraarylbutadiene is a representative electrochromic dye, and the same chromophore can be found in 9,10-bis(diarylmethylene)-9,10-dihydrophenanthrene (dibenzo-oQD) albeit in a fixed s- cis geometry. Unlike thermodynamically unstable 7,7,8,8-tetraaryl- o -quinodimethane, spontaneous electrocyclization is prohibited by dibenzo-annulation. Several derivatives of dibenzo-oQD were successfully generated despite highly strained geometry caused by steric hindrance between the bulky diarylmethylene units. Their precursors are phenanthrene-9,10-diyl bis(diarylmethylium) dyes (PDM 2+ ) stabilized by four electron-donating alkoxy groups. The redox pairs of dibenzo-oQD/PDM 2+ exhibit vivid change in color upon redox interconversion (electrochromism). Both dibenzo-oQD and PDM 2+ adopt a helical conformation, whose configuration is unstable. When a chiral alkoxy substituent is attached on each of the aryl groups, the point chirality is successfully transmitted to helicity of PDM 2+ . Resulting diastereomeric biasing is the key for dibenzo-oQD/PDM 2+ to exhibit the two-way-output response (e.g., UV–vis and CD). In addition, much more strained quinodimethane derivatives, 1,2-bis(diarylmethylene)acenaphthene and 1,16-diaryldibenzo[ b,n ]perylene, were also generated from the dicationic precursors, demonstrating that the reductive transformation can serve as a useful protocol to generate severely deformed π-conjugated systems.

Singlet biradicaloids are certainly one of the most frequently discussed topics at ISNA-15. In this review our own work on the synthesis, molecular structures, and physical properties relevant to biradical character of indenofluorene isomers are described. These include indeno[2,1- a ]fluorene with an o -quinodimethane substructure, benz[ c ]indeno[2,1- a ]fluorene which is the first 2,3-naphthoquinodimethane derivative isolated, and indeno[2,1- b ]fluorene with an m -quinodimethane ( m -xylylene) subunit. The observed physical properties are explained in terms of the theoretically derived biradical factors (y), HOMO-LUMO energy gaps, and singlet-triplet energy gaps in the ground state electronic configurations. In addition, we discuss here two perspectives in the biradicaloid chemistry, (i) two- and three-dimensional indenofluorene congeners arranged in a macrocyclic form and (ii) macrocyclic indenofluorenes having multiple radical characters.

Zethrene and its related molecules have attracted much attention from the perspectives of both synthetic chemistry and materials science. One characteristic feature of these molecules is the existence of two distinct resonance structures, a closed-shell quinoidal form and an open-shell biradical form, which will lead to a significant biradical contribution to the ground-state electronic configuration. As a result, zethrene-based molecules exhibit unique optical, electronic, and magnetic properties, which open the door for a diversity of applications in the field of electronics, nonlinear optics, and spintronics.

Numerous highly curved fragments of C 60 and unique subunits of C 70 were synthesized under mild conditions using metal-catalyzed protocols. According to X-ray crystallographic analyses, highly curved fragments of C 60 have a maximum π-orbital axis vector (POAV) pyramidalization angle of up to 12.9 °, whereas distinctive fragments of C 70 , analogous to the tube portion of the rugby-shaped buckyball, are less curved. Among the eight buckybowls studied herein, five form polar crystals. Depending on the molecular geometry, the inversion dynamics of buckybowls involves either a planar or an S-shaped (non-planar) transition structure.

The widespread use of thermal analysis (TA) by scientists as a laboratory technique carries with it a working vocabulary. This document is intended to provide those working in the field with a consistent set of definitions to permit clear and precise communication as well as understanding. Included in the document are the definitions of 13 techniques, 54 terms within the glossary, as well as symbols and units.