Polymers linear conjugated

This article summarizes efforts undertaken towards the synthesis of the cyclo[ ]carbons, the first molecular carbon allotropes for which a rational preparative access has been worked out. Subsequently, a diversity of perethynylated molecules will be reviewed together, they compose a large molecular construction kit for acetylenic molecular scaffolding in one, two and three dimensions. Finally, progress in the construction and properties of oligomers and polymers with a poly(triacetylene) backbone, the third linearly conjugated, non-aromatic all-carbon backbone, will be reviewed. 

Oxidative polymerization of trans-bis-deprotected 79 under Hay coupling conditions [54] yielded, after end-capping with phenylacetylene, the high-melting and readily soluble oligomers 80a-e with the poly (triacetylene) backbone [87,106] (Scheme 8). Poly(triacetylene)s [PTAs,-(C=C-CR=CR-C=C) -] are the third class of linearly conjugated polymers with a non-aromatic allcarbon backbone in the progression which starts with polyacetylene [PA,... 

Many of the linear conjugated tricyclic systems have interesting fluorescence or other electrophysical properties. Bis-pyrazolepyridines such as compound 30 have been incorporated into polymers as fluorescent chromophores <1999JMC339>, and used in doped polymer matrices <1997JMC2323>. They are electroluminescent at 425 nm and photoluminescent at 427 and 430 nm in a poly(vinylcarbazole) matrix with a quantum efficiency of 0.8. 

Polythiophenes (including oligothiophenes) are one of the most studied and important classes of linear conjugated polymers [444,445], Versatile synthetic approaches to PTs (chemical [446] and electrochemical [447]), easy functionalization and unique, widely tunable electronic properties have been the source of tremendous interest in this class of polymers. 

Several groups have engaged in the study of linear polymer-dendrimer conjugates (i.e. architectural copolymers). These structures combine block copolymer and dendrimer branching features within one molecular architecture [69-71],... 

Those olefins having double bonds sufficiently electron rich to react significantly with these salts include the common monomers, alkyl vinyl ethers (28,79-81), N-vinylcarbazole (82-84) p-methoxystyrene (21,67), indene (34,74,85), cyclopen tadiene (85,86), and vinylnaphthalenes (87). Styrene itself (60,76,77,88-91), cr-divinylbenzene (92), a-methylstyrene (88), linear conjugated dienes (93) and a-olefins are much less reactive (i.e. formation of their corresponding carbocations is energetically unfavourable), and undo- normal conditions give at best slow reactions and low yields of polymer. 

Berlin, A. A., B. I. Liogon kii, V. P. Parini, and M. S. Leikina Polymers with conjugated double bonds and heteroatoms in the chain. XXXV. Linear aromatic polymers with methylene groups between the benzene rings. Vysoko-mol. Soed. 4, 662 (1962) [4, 221 (1962)]. 

Linear polymers from conjugated dienes readily undergo oxidation in air, in some cases even at room temperature (14). The allylic carbon... 

In a recent study, avidin was extensively modified with linear 5- and 10-kDa PEGs and with a branched 20-kDa PEG. In order to maintain high biological activity, the polymer was conjugated in the presence of a macromolecular active site protective agent, which was used to avoid polymer attachment on the protein area... 

Below, the one-dimensional band structure of simple linear conjugated polymers is outlined, followed by a brief description of the use of some model 7t-conjugated molecules for conjugated polymers. Then, to close out the chapter, the description of the properties of conjugated polymers is extended to issues of optical absorption and photo-luminescence. 

One-dimensional band structure of linear conjugated polymers... 

Linearly -Conjugated Oligomers and Polymers Poly(triacetylene)s 209... 

The initial application of quantum mechanics to the electronic states of a perfect linear conjugated chain, as in the Htickel model discussed in Section 4.2.5 and above, led to a model of a one-dimensional semiconductor with well-defined valence and conduction bands. This labelling of the electronic states is widespread in the literature. On the other hand, when electron correlation is included, the electronic states are more localised and an exciton description is more appropriate. The disorder present in all but a few exceptional cases inevitably leads to the conclusion that the electronic states must be localised by chain defects. The extent to which the electronic states of conjugated polymers are localised, i.e. deviate from the band model, has been a matter of debate. There is a growing body of experimental and theoretical evidence, discussed in Sections 9.4.2 and 9.4.3 below, that suggests that the exciton description is closer to the truth. 

In the examples of our work on organic molecular and polymeric solids that follow, first some contributions to the UPS line widths in condensed molecular solids are discussed for two prototype systems, anthracene and isopropyl benzene then the UPS of two.aromatic pendant group polymers, polystyrene and poly(2-vinyl pyridine), are discussed and compared with some spectra concerning the simplest linear conjugated polymer, polyacetylene. 

Wegner, G. Organic linear polymers with conjugated double bonds. In Chemistry and physics of one-dimensional metals. Keller, H. J. (ed.). New York Plenum Press 1977, pp. 297-314... 

The two-fold coordination associated with linear conjugated polymers and the proportionality of bond length to bond strength (or bond order [7]) in conjugated systems, leads to a deep interconnection between their electronic and chemical structures [8-13]. As a result of this interconnection, the elementary... 

A different subclass of unsaturated hydrocarbon type polymers is formed by polyacetylenes. This type of polymer contains conjugated double bonds in a linear structure, and due to their special electrical properties they have been the subjects of numerous studies including some on thermal stability. 

Kijima, M. Kinoshita, L Shirakawa, H. Synthesis and characterization of a novel linear conjugated polymer, poly(2,5-didodecyloxy-l,4-phenyleneocta-tetraynylene) Chem. Lett. 1999, (6), 531-532. 

Cataldo, F. On the action of polymers having unconjugated and cross or linearly conjugated unsaturations chemistry technological aspects. Polym. Deg. Stab. 2001, 73, 511. 

Polyacetylene (PA), the simplest linear conjugated polymer, has been actively studied for two main reasons. First, the discovery of the direct synthesis method of PA films on the surface of a Ziegler-Natta catalyst solution [1]. Second, the discovery of a large increase in electronic conductivity, due to a synthetic metal by doping with small quantities of electron-attracting species such as iodine, AsFs, etc., or with an electron donor such as sodium. However, because of its high reactivity and poor solubility, it is difficult to obtain the experimental structural data of PA. 

The energy barrier for hole injection at the metal-poymer interface is determined by the vacuum work function of the metal contact and the ionization potential Ip of the polymer. For conjugated polymer films spin-coated onto hole injecting metal electrodes, it has been reported that as long as is smaller than a critical value characteristic of the polymer, no interface dipole is formed [104]. In this case, the barrier for hole injection can be estimated simply by aligning the vacuum levels of the metal and the polymer (Mott-Schottky limit) the measured work function of the metal with the polymer deposited on top increases linearly with with a slope of one (see Figure 2.3.11). 

Poly(ferrocenylene vinylene) derivatives 68 with values of 3,000-10,000 and polydispersities of ca. 2.2-2.8 (determined by GPG) were synthesized in 1995 in high yields via a titanium-induced McMurry coupling reaction of the corresponding alkylferrocenyl carbaldehyde monomers (Equation (26)). " Gharacterization of these soluble polymers by NMR and IR revealed the presence of trans-Yinylcnc units. The UV-VIS spectra of the polymers are similar to those of the monomers and this indicates a fairly localized electronic structure in the former. The relatively limited electron localization is also reflected in the electrical and optical properties. For example, the values for iodine-doped conductivity a= 10 Scm ) and non-linear third-order optical susceptibility (x = 1-4 x 10 esu) are lower than those of linear conjugated polymers such as poly(l,4-phenylene-vinylene) (a = 2.5x 10 Scm" = 8 X 10 esu). 

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