Ethynylene

Poly(l,3,4-oxadia2ole-2,5-diyl-vinylene) and poly(l,3,4-oxadia2ole-2,5-diyl-ethynylene) were synthesi2ed by polycondensation of fumaramide or acetylene-dicarboxamide with hydra2ine sulfate in PPA to study the effect of the two repeating units on polymer electronic and thermal properties (55). 

Optically active polymers, 473, 479-480 synthesis of, 509 Optically active poly(phenylene-ethynylene), synthesis of,... 

We shall find it convenient to divide the data sets for substituent effects at carbon—carbon triple bonds into three categories acetylene, ethynylene, and reactions at carbon—carbon triple-bond sets. 

We find that it will be useful to divide the ethynylene sets into two categories sets involving properties of the ethynyl proton in substituted acetylenes, and the other ethynylene sets. 

Data are extant in the literature for two other sets of ethynylene compounds. The sets studied are reported in Table XXXIII. Results of correlation are set forth in Table XXXIV and values of Pr in Table XXXV. The ionization constants of 3-substituted propiolic acids, which were first correlated with the Hammett equation by Charton (18), gave an excellent correlation with eq. (2) (set 22-27-1). The results are very much improved by the elimination of the value for X = H (set 33-27-2). The composition of the electrical effect corresponds approximately to that of the Op constants. The magnitude of the electrical effect is significantly less than that observed for the rrans-3-substituted acrylic acids. 

The paucity of data for substituted ethynylene sets is remarkable. Before any definitive conclusions concerning the transmission of substituent effects by the triple bond can be made, much further investigation is required. This field is one which is certainly worthy of further inquiry. 

The trans,trans-dmnylene group has a Pr value of 57, somewhat greater than the pr values observed for p-phenylene, rrans-vinylene, and ethynylene. 

In line with a second novel synthetic principle, the authors further developed the repetitive Diels-Alder procedure, in which monomers containing cyclopentadienone (dienophile) units were reacted with protected/deprotected ethynylene functions (see [31]). In this way, they generated a novel class of highly arylated phenylene dendrimers 46, starting from a 3,3, 5,5 -tetraethynyl-substituted biphenyl core [60]. 

This modular methology involves the repetition of directed protection/cyclo-addition/deprotection steps, and allows for the synthesis of monodisperse dendritic oligophenylenes of the first (46a, 22 benzene rings) and second (46b, 62 benzene rings) generation [60]. Within the synthetic sequence, the authors made use of the different reactivities of protected and deprotected ethynylene functions within the key cycloadditon step. 

Grignard chemistry was used as an alternative to hydroboration reaction by the Chujo team in its search for new n-type conjugated polymers for utilization in polymer energy storage systems. By this route, the syntheses of 7r-conjugated poly(p-phenylene-boranes) (15)35 (Fig. 12) and poly(ethynylene-phenylene-ethynylene-borane)s were reported.36... 

Figure 89 The motorized nanocar structure (172) that contains a light-activated unidirectional molecular motor and an oligo(phenylene ethynylene) chassis and axle system with four carboranes to serve as the wheels. (Adapted from ref. 168.)... 

Poly(ethynylene-p-phenylene-ethynylene-borane)s were also prepared by polycondensations of bifunctional lithium acetylides and aryldimethoxyborane, as shown in scheme 35.61 The polymerization between dilithium 2,5-didodecyloxybenzene-1,4-diethynilide and tripyldimethoxyborane gave the corresponding polymer in 67%... 

Zhang, Y. Synchrotron Radiation Direct Photo Etching of Polymers. Vol. 168, pp. 291-340. Zheng, J. and Swager, T. M. Polyfarylene ethynylene)s in Chemosensing and Biosensing. Vol. 177, pp. 151-177. 

Polymeric (isocyanide)gold(i) aryls ( gold oligo-phenylene-ethynylene-isonitriles ) were tested as electrical conductors at metal-molecule-metal junctions (7r-conjugated molecular wires), but the preparation, structure, and properties of the materials were not fully disclosed (Scheme 52).218... 

Xiao X, Nagahara LA, Rawlett AM, Tao N (2005) Electrochemical gate-controlled conductance of single oligo(phenylene ethynylene)s. J Am Chem Soc 127 9235-9240... 

It has been reported that the electrical properties of single molecules incorporating redox groups (e.g. viologens [114, 119, 120, 123, 124], oligophenylene ethynylenes [122, 123], porphyrins [111, 126], oligo-anilines and thiophenes [116, 127], metal transition complexes [118,128-132], carotenes [133], ferrocenes [134,135],perylene tetracarboxylic bisimide [93, 136, 137] and redox-active proteins [138-143]), can be switched electrochemically. Such experiments, typically performed by STM on redox-active molecules tethered via Au-S bonds between a gold substrate and a tip under potential control, allow the possibility to examine directly the correlation between redox state and the conductance of individual molecules. 

Apolar m-phenylene ethynylene oligomers 77 fold in apolar solvents, such as alkanes, into helices.117 Due to the strongly favored arene-arene interactions in this solvent type, the folding into a helical oligomer coincides with stacking of the folded oligomers into helical columnar polymers and a strong... 

Abstract Described are the synthetic routes to precisely defined molecular wires which are of discrete length and constitution. They are fully conjugated systems and are expected to have nearly linear current-voltage response curves. Their ends are functionalized with molecular alligator clips, based on chalconides and isonitriles, for adhesion between proximal probes. Both solution and solid-phase approaches have been used to prepare these molecular wires that are based on oligofthiophene ethynylene)s and oligofphe-nylene ethynylene)s. Molecular device syntheses are also described that would be expected to have nonlinear current-voltage responses. 

Figure 2. Solution phase synthesis of the oligo(thiophene ethynylene)s by the divergent/convergent doubling approach.

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