Synthesis, characterization, and solid-state polymerization of cross-conjugated octatetraynes

Two series of cross-conjugated 1,3,5,7-octatetraynes (1a–1l and 6a–6d) have been synthesized. UV–vis spectroscopic analysis shows that pendent groups connected to the cross-conjugated skeleton have little effect on the λmax energies, irrespective of whether the groups are electron withdrawing or donating. A number of the isolated products readily give crystals suitable for X-ray crystallography, and the solid-state structural properties of five derivatives (1k, 1l, 6a, 6c, and 6d) have been examined by X-ray crystallographic analysis. Parallel packing of the polyynes in the solid state indicates that four of the five samples are potentially suitable for topochemical polymerization, based on solid-state packing parameters θ, R, and d. Attempts to effect a solid-state reaction have been explored through UV–vis and γ-ray irradiation as well as thermal heating. The course of these reactions was monitored by differential scanning calorimetry (DSC) analysis, as well as UV–vis and solid-state 13C NMR spectroscopy (for 1d, 1j, 1k, and 6d), which offered evidence of polymer formation from these reactions. Structural determination of the product(s), however, remains elusive.

Porphyrinic assemblies of pyridine-containing macrocycles

Using a combination of palladium-catalyzed cross-coupling and copper-catalyzed homocoupling reactions, two pyridine-containing macrocycles with varying pendant substitution were constructed. Their synthesis and subsequent coordination to a ruthenium porphyrin is described. In addition to synthetic details and characterization, an examination of their electronic properties is provided.

Shape-persistent macrocycles — Self-assembly reactions and characterization by hyperpolarized 129Xe NMR spectroscopy**In memory of Professor Michael M. Pollard

The use of three shape-persistent, conjugated macrocycles 2a–2c as ligands for self-assembly reactions is described. The macrocycles have been characterized through a combination of spectroscopic analyses and, for compounds 2b and 2c, X-ray crystallographic analysis. Whereas the reaction of 2a with the cis-Pt(II) species 3 successfully provides the porous solid 4a, the analogous reaction of 2b and 2c with 3 leads only to mixtures of products. The application of continuous-flow hyperpolarized 129Xe NMR spectroscopy to investigate the solid-state pores of macrocycles 2b and 2c and the supramolecular complex 4a as a function of temperature is described. All three species show permanent porosity upon removal of co-crystallized solvent molecules. Using trends in the 129Xe chemical shifts and temperature-dependent dynamics of Xe atoms in the solids, information is obtained on the nature of the pores in these systems. Using the 129Xe NMR data for complex 4a, the effective heat of adsorption (ΔHads) was calculated to be ~29 kJ mol–1.

Conjugated Oligomers and Polymers Based on Anthracene, Tetracene, Pentacene, Naphthodithiophene, and Anthradithiophene Building Blocks

Acene derivatives provide unique materials for organic semiconductor applications. Recent synthetic achievements have provided several oligomers and polymers based on acene building blocks of varied structural motifs, including anthracene, tetracene, pentacene, as well as naphtho- and anthradithiophene. This report highlights recent work in this area, particularly for the higher acenes tetracene, pentacene, and anthradithiophene. When possible, the properties of defined-length oligomers are compared and contrasted to those of mono- and polymeric systems.

The Fritsch-Buttenberg-Wiechell rearrangement: modern applications for an old reaction

The Fritsch-Buttenberg-Wiechell rearrangement of carbene/carbenoid intermediates has evolved into a valuable synthetic methodology for the preparation of polyyne structures. Various synthetic routes toward the formation of the corresponding precursors, alkynyl-substituted dibromoolefins, have been developed. Additionally, the scope of this methodology is expanded significantly by the development of functional group-tolerant one-pot procedures. The preparation of various polyynes up to the octa- and decaynes is, thus, possible on a scale that enables thorough physico-chemical characterization. Hence, series of polyynes have been investigated by, e.g., UV-vis, IR- and Raman spectroscopy, as well as X-ray crystallography. These investigations give unique insight into the structural characteristics of longer polyynes and hint to the structure of carbyne.

Toward carbyne: Synthesis and stability of really long polyynes

Molecules composed of sp-hybridized carbon chains (polyynes) are the simplest of the known conjugated organic oligomers. In comparison to their counterparts such as polyacetylene and polydiacetylene, however, the formation of polyynes has traditionally posed a difficult synthetic challenge. In particular, there is no reliable method to form end-capped polyethynylene, and monodisperse polyynes have therefore been assembled. As a result, structure–property relationships for shorter polyynes have been relatively well established in recent years, while extension of these trends toward longer polyynes has remained a difficult task. Using the Fritsch–Buttenberg–Wiechell (FBW) rearrangement, the formation of diynes through decaynes has become possible and has provided a unique chance to explore the physical characteristics of conjugated polyyne chains. This paper highlights recent advances in the synthesis of extended polyynes, as well as interesting aspects of their NMR, Raman, and UV/vis spectroscopic analyses. These synthetic achievements offer the opportunity to predict some of the properties of the carbon allotrope carbyne. In particular, a set of X-ray crystallographic analyses of t-Bu end-capped polyynes (tBu[n]) shows a definitive experimental trend in reduced bond-length alternation (BLA).

Naturally occurring and synthetic polyyne glycosides

Polyyne glycosides are a class of natural products that have been found in terrestrial plants, fungi, and marine algae. Many display interesting and potentially useful biological activities, which in some cases has initiated synthetic efforts toward their formation. This review provides a comprehensive report of polyyne glycosides isolated from natural sources, as well as the synthesis of these molecules and their analogues.

Exploring electronically polarized pentacenes

Unsymmetrically functionalized pentacenes with electron-rich and/or -poor substituents at the 6- and 13-positions were synthesized. The electronic influence was evaluated by solution-state UV-vis absorption and emission spectroscopies. These materials exhibit good solubility in common organic solvents and are stable in the presence of air and water.

Regioselective Trapping of Terminal Di-, Tri-, and Tetraynes with Benzyl Azide

[Structure: see text] The reaction of benzyl azide with terminal di-, tri-, and tetraynes appended with a range of functional groups has been explored. Standard reaction conditions for BnN3 catalyzed by CuSO4.5H2O gave alkynyl, butadiynyl, and hexatriynyl triazoles in moderate to good yields. The reaction proceeds regioselectively as determined by the X-ray crystallographic analysis of three derivatives (1c, 1d, and 3c), and no evidence of multiple azide addition to the polyyne framework is observed.

Two-photon absorption in two-dimensional conjugated quadrupolar chromophores

We present ultrafast z-scan measurements of the two-photon absorption (TPA) spectra of a pair of two-dimensionally conjugated quadrupolar donor/acceptor (D/A) chromophores. The all-donor substituted species displays a peak TPA cross section [sigma(2)=520+/-30 GM] that is more than twice that of the D-A species [sigma(2)=240+/-20 GM]. Unlike previous structure-property studies that have evaluated TPA behavior for D/A molecules through the comparison of dipolar and quadrupolar compounds, both molecules investigated herein are quadrupolar, ultimately providing a more consistent evaluation of the effects of donor and/or acceptor substitution on the TPA of conjugated chromophores.

Synthesis and Stability of a Homologous Series of Triynol Natural Products and Their Analogues

A series of polyyne natural products 1, 13, and 31 and analogues 14, 21, and 22 are synthesized in six steps. The key step is a Fritsch-Buttenberg-Wiechell rearrangement in which a triyne framework is formed from the appropriate dibromoolefin precursor. Terminal conjugated triynes 13 and 14 are obtained as highly unstable products that rapidly decompose under ambient conditions. The stability of triynols increases via either the addition of methylene units (i.e., 6 --> 31 --> 1) or addition of terminal substituents (i.e., 13 --> 21 or 31).

Synthesis, structure, and nonlinear optical properties of diarylpolyynes

A series of alpha,omega-diarylpolyynes has been synthesized. In addition to the synthesis of three hexaynes (3a-c), a notably improved synthesis of 1,16-diphenylhexadecaoctayne (5) is described. The third-order nonlinear optical characteristics for these molecules have been studied and show a substantial increase in molecular hyperpolarizability (gamma) as a function of increasing length. The unusual solid-state structures of compounds 3a and 3b are reported.