Synthesis and Properties of Molecular Rods. 2. Zig-Zag Rods

Electro-functional octupolar π-conjugated columnar liquid crystals

A series of propeller-shaped π-conjugated molecules based on 2,4,6-tris(thiophene-2-yl)-1,3,5-triazines has been designed and synthesized to obtain ambipolar charge-transporting liquid-crystalline materials. The 3-fold electron-donating aromatic units are attached to the electron-accepting triazine core, which forms electro-functional octupolar π-conjugated structures. These octupolar molecules self-organize into one-dimensional columnar nanostructures and exhibit ambipolar carrier transport behavior, which has been revealed by time-of-flight measurements. In this approach, electron-donor and acceptor electro-active segments are assembled individually in each column to give one-dimensional nanostructured materials with precisely tuned electronic properties. Their desirable electronic structures responsible for both hole and electron conductions have also been examined by cyclic voltammetry and theoretical calculations. The present results provide a new guideline and versatile approach to the design of ambipolar conductive nanostructured liquid-crystalline materials.

High-nuclearity Pt-Tl-Fe complexes: structural, electrochemistry, and spectroelectrochemistry studies

A series of heteropolynuclear Pt-Tl-Fe complexes have been synthesized and structurally characterized. The final structures strongly depend on the geometry of the precursor and the Pt/Tl ratio used. Thus, the anionic heteroleptic cis-configured [cis-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and [Pt(bzq)(C≡CFc)(2)](-) (Fc = ferrocenyl) complexes react with Tl(+) to form discrete octanuclear (PPh(3)Me)(2)[{trans,cis,cis-PtTl(C(6)F(5))(2)(C≡CFc)(2)}(2)] (1), [PtTl(bzq)(C≡CFc)(2)](2) (5; bzq = benzoquinolate), and decanuclear [trans,cis,cis-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](2) (3) derivatives, stabilized by both Pt(II)···Tl(I) and Tl(I)···η(2)(alkynyl) bonds. By contrast, Q(2)[trans-Pt(C(6)F(5))(2)(C≡CFc)(2)] (Q = NBu(4)) reacts with Tl(+) to give the one-dimensional (1-D) anionic [(NBu(4)){trans,trans,trans-PtTl(C(6)F(5))(2)(C≡CFc)(2)}](n) (2) and neutral [trans,trans,trans-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](n) (4) polymeric chains based on [PtFc(2)](2-) platinate fragments and Tl(+) (2) or [Tl···Tl](2+) (4) units, respectively, connected by Pt(II)···Tl(I) and secondary weak κ-η(1) (2) or η(2) (4) alkynyl···Tl(I) bonding. The formation of 1-4 is reversible, and thus treatment of neutral 3 and 4 with PPh(3)MeBr causes the precipitation of TlBr, returning toward the formation of the anionic 1 and 2' (Q = PPh(3)Me). Two slightly different pseudopolymorphs were found for 2', depending on the crystallization solvent. Finally, the reaction of the homoleptic [Pt(C≡CFc)(4)](2-) with 2 equiv of Tl(+) affords the tetradecanuclear sandwich type complex [Pt(2)Tl(4)(C≡CFc)(8)] (6). Electrochemical, spectroelectrochemical, and theoretical studies have been carried out to elucidate the effect produced by the interaction of the Tl(+) with the Pt-C≡CFc fragments. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of 1-5 reveal that, in general, neutralization of the anionic fragments increases the stability of the fully oxidized species and gives higher E(1/2) (Fc) values than those observed in their precursors, increasing with the number of Pt-Tl bonding interactions. However, the electronic communication between Fc groups is reduced or even lost upon Tl(+) coordination, as confirmed by electrochemical (CVs and DPVs voltammograms, 1-5) and spectroelectrochemical (UV-vis-NIR, 2-4) studies. Complexes 2 and 4 still display some electronic interaction between the Fc groups, supported by the presence of an IVCT band in their UV-vis-NIR spectra of oxidized species and additional comparative DFT calculations with the precursor [trans-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and complex 3.

Nanoscale optoelectronic switches and logic devices

The photoelectrochemical photocurrent switching (PEPS) effect, in the beginning regarded as a scientific curiosity, has become a field of extensive study for numerous research groups all over the world. This unique effect can be utilized for nanoscale switching and information processing, furthermore, is can serve as an interface between molecular information processing and macroscopic electronics. This review summarizes recent efforts in understanding photocurrent switching effects and their application for the construction of nanoscale switches and logic devices. Furthermore, some future prospects concerning the development of electronic/optoelectronic devices based on photoactive semiconducting hybrid materials are presented.

Self-organized porphyrinic materials

The self-assembly and self-organization of porphyrins and related macrocycles enables the bottom-up fabrication of photonic materials for fundamental studies of the photophysics of these materials and for diverse applications. This rapidly developing field encompasses a broad range of disciplines including molecular design and synthesis, materials formation and characterization, and the design and evaluation of devices. Since the self-assembly of porphyrins by electrostatic interactions in the late 1980s to the present, there has been an ever increasing degree of sophistication in the design of porphyrins that self-assemble into discrete arrays or self-organize into polymeric systems. These strategies exploit ionic interactions, hydrogen bonding, coordination chemistry, and dispersion forces to form supramolecular systems with varying degrees of hierarchical order. This review concentrates on the methods to form supramolecular porphyrinic systems by intermolecular interactions other than coordination chemistry, the characterization and properties of these photonic materials, and the prospects for using these in devices. The review is heuristically organized by the predominant intermolecular interactions used and emphasizes how the organization affects properties and potential performance in devices.

A hierarchy of homodesmotic reactions for thermochemistry

Chemical equations that balance bond types and atom hybridization to different degrees are often used in computational thermochemistry, for example, to increase accuracy when lower levels of theory are employed. We expose the widespread confusion over such classes of equations and demonstrate that the two most widely used definitions of "homodesmotic" reactions are not equivalent. New definitions are introduced, and a consistent hierarchy of reaction classes (RC1-RC5) for hydrocarbons is constructed: isogyric (RC1) superset of isodesmic (RC2) superset of hypohomodesmotic (RC3) superset of homodesmotic (RC4) superset of hyperhomodesmotic (RC5). Each of these successively conserves larger molecular fragments. The concept of isodesmic bond separation reactions is generalized to all classes in this hierarchy, providing a unique sectioning of a given molecule for each reaction type. Several ab initio and density functional methods are applied to the bond separation reactions of 38 hydrocarbons containing five or six carbon atoms. RC4 and RC5 reactions provide bond separation enthalpies with errors consistently less than 0.4 kcal mol(-1) across a wide range of theoretical levels, performing significantly better than the other reaction types and far superior to atomization routes. Our recommended bond separation reactions are demonstrated by determining the enthalpies of formation (at 298 K) of 1,3,5-hexatriyne (163.7 +/- 0.4 kcal mol(-1)), 1,3,5,7-octatetrayne (217.5 +/- 0.6 kcal mol(-1)), the larger polyynes C(10)H(2) through C(26)H(2), and an infinite acetylenic carbon chain.